feat: 实现 Android 标尺测量应用完整代码

app/build.gradle.kts

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+plugins {
+    id("com.android.application")
+    id("org.jetbrains.kotlin.android")
+}
+
+android {
+    namespace = "com.example.androidruler"
+    compileSdk = 34
+
+    defaultConfig {
+        applicationId = "com.example.androidruler"
+        minSdk = 24
+        targetSdk = 34
+        versionCode = 1
+        versionName = "1.0"
+    }
+
+    buildTypes {
+        release {
+            isMinifyEnabled = false
+            proguardFiles(getDefaultProguardFile("proguard-android-optimize.txt"), "proguard-rules.pro")
+        }
+    }
+
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_17
+        targetCompatibility = JavaVersion.VERSION_17
+    }
+
+    kotlinOptions {
+        jvmTarget = "17"
+    }
+
+    buildFeatures {
+        compose = true
+    }
+
+    composeOptions {
+        kotlinCompilerExtensionVersion = "1.5.8"
+    }
+
+    packaging {
+        resources {
+            excludes += "/META-INF/{AL2.0,LGPL2.1}"
+        }
+    }
+}
+
+dependencies {
+    val composeBom = platform("androidx.compose:compose-bom:2024.06.00")
+    implementation(composeBom)
+
+    implementation("androidx.core:core-ktx:1.12.0")
+    implementation("androidx.lifecycle:lifecycle-runtime-ktx:2.7.0")
+    implementation("androidx.activity:activity-compose:1.8.2")
+
+    implementation("androidx.compose.ui:ui")
+    implementation("androidx.compose.ui:ui-graphics")
+    implementation("androidx.compose.ui:ui-tooling-preview")
+    implementation("androidx.compose.material3:material3")
+    implementation("androidx.compose.material:material-icons-extended")
+
+    implementation("androidx.lifecycle:lifecycle-viewmodel-compose:2.7.0")
+    implementation("androidx.datastore:datastore-preferences:1.0.0")
+
+    val cameraxVersion = "1.3.4"
+    implementation("androidx.camera:camera-core:${cameraxVersion}")
+    implementation("androidx.camera:camera-camera2:${cameraxVersion}")
+    implementation("androidx.camera:camera-lifecycle:${cameraxVersion}")
+    implementation("androidx.camera:camera-view:${cameraxVersion}")
+
+    debugImplementation("androidx.compose.ui:ui-tooling")
+    debugImplementation("androidx.compose.ui:ui-test-manifest")
+}

app/proguard-rules.pro

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+# Add project specific ProGuard rules here.

app/src/main/AndroidManifest.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+
+    <uses-permission android:name="android.permission.CAMERA" />
+    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"
+        android:maxSdkVersion="28" />
+    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"
+        android:maxSdkVersion="32" />
+    <uses-permission android:name="android.permission.READ_MEDIA_IMAGES" />
+
+    <uses-feature android:name="android.hardware.camera" android:required="false" />
+
+    <application
+        android:name=".RulerApplication"
+        android:allowBackup="true"
+        android:dataExtractionRules="@xml/backup_rules"
+        android:fullBackupContent="@xml/backup_rules"
+        android:label="@string/app_name"
+        android:supportsRtl="true"
+        android:theme="@style/Theme.AndroidRuler">
+
+        <activity
+            android:name=".MainActivity"
+            android:exported="true"
+            android:configChanges="orientation|screenSize|screenLayout">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.LAUNCHER" />
+            </intent-filter>
+        </activity>
+    </application>
+</manifest>

app/src/main/java/com/example/androidruler/MainActivity.kt

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+package com.example.androidruler
+
+import android.os.Bundle
+import androidx.activity.ComponentActivity
+import androidx.activity.compose.setContent
+import androidx.activity.enableEdgeToEdge
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.padding
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.filled.Settings
+import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.material3.Icon
+import androidx.compose.material3.IconButton
+import androidx.compose.material3.Scaffold
+import androidx.compose.material3.Text
+import androidx.compose.material3.TopAppBar
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Modifier
+import androidx.lifecycle.viewmodel.compose.viewModel
+import com.example.androidruler.theme.AndroidRulerTheme
+import com.example.androidruler.ui.ControlBar
+import com.example.androidruler.ui.RulerScreen
+import com.example.androidruler.ui.photo.PhotoMarkScreen
+import com.example.androidruler.ui.settings.SettingsScreen
+import com.example.androidruler.viewmodel.Mode
+import com.example.androidruler.viewmodel.RulerViewModel
+
+class MainActivity : ComponentActivity() {
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        enableEdgeToEdge()
+        setContent {
+            AndroidRulerTheme {
+                MainApp()
+            }
+        }
+    }
+}
+
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+fun MainApp(viewModel: RulerViewModel = viewModel()) {
+    if (viewModel.showSettings) {
+        SettingsScreen(
+            currentOrientation = viewModel.defaultOrientation,
+            currentRulerLength = viewModel.overlayRulerLength,
+            correctionFactor = viewModel.cmCorrectionFactor,
+            onBack = { viewModel.showSettings = false },
+            onSave = { orientation, length, factor ->
+                viewModel.updateSettings(orientation, length, factor)
+            }
+        )
+    } else {
+        Scaffold(
+            topBar = {
+                TopAppBar(
+                    title = { Text("标尺") },
+                    actions = {
+                        IconButton(onClick = { viewModel.showSettings = true }) {
+                            Icon(Icons.Default.Settings, contentDescription = "设置")
+                        }
+                    }
+                )
+            },
+            bottomBar = {
+                ControlBar(
+                    currentMode = viewModel.mode,
+                    onModeChange = { viewModel.mode = it }
+                )
+            }
+        ) { padding ->
+            Box(modifier = Modifier.padding(padding).fillMaxSize()) {
+                when (viewModel.mode) {
+                    Mode.RULER -> RulerScreen(viewModel = viewModel)
+                    Mode.PHOTO -> PhotoMarkScreen(viewModel = viewModel)
+                }
+            }
+        }
+    }
+}

app/src/main/java/com/example/androidruler/RulerApplication.kt

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+package com.example.androidruler
+
+import android.app.Application
+
+class RulerApplication : Application()

app/src/main/java/com/example/androidruler/data/SettingsRepository.kt

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+package com.example.androidruler.data
+
+import android.content.Context
+import androidx.datastore.preferences.core.booleanPreferencesKey
+import androidx.datastore.preferences.core.edit
+import androidx.datastore.preferences.core.floatPreferencesKey
+import androidx.datastore.preferences.core.stringPreferencesKey
+import androidx.datastore.preferences.preferencesDataStore
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.map
+
+private val Context.dataStore by preferencesDataStore(name = "ruler_settings")
+
+class SettingsRepository(private val context: Context) {
+
+    companion object {
+        private val KEY_CORRECTION_FACTOR = floatPreferencesKey("cm_correction_factor")
+        private val KEY_IS_CALIBRATED = booleanPreferencesKey("is_calibrated")
+        private val KEY_DEFAULT_ORIENTATION = stringPreferencesKey("default_orientation")
+        private val KEY_DEFAULT_RULER_LENGTH = floatPreferencesKey("default_ruler_length")
+    }
+
+    val correctionFactor: Flow<Float> = context.dataStore.data.map { prefs ->
+        prefs[KEY_CORRECTION_FACTOR] ?: 1.0f
+    }
+
+    val isCalibrated: Flow<Boolean> = context.dataStore.data.map { prefs ->
+        prefs[KEY_IS_CALIBRATED] ?: false
+    }
+
+    val defaultOrientation: Flow<String> = context.dataStore.data.map { prefs ->
+        prefs[KEY_DEFAULT_ORIENTATION] ?: "auto"
+    }
+
+    val defaultRulerLength: Flow<Float> = context.dataStore.data.map { prefs ->
+        prefs[KEY_DEFAULT_RULER_LENGTH] ?: 3.0f
+    }
+
+    suspend fun setCorrectionFactor(factor: Float) {
+        context.dataStore.edit { prefs ->
+            prefs[KEY_CORRECTION_FACTOR] = factor
+            prefs[KEY_IS_CALIBRATED] = true
+        }
+    }
+
+    suspend fun setDefaultOrientation(orientation: String) {
+        context.dataStore.edit { prefs ->
+            prefs[KEY_DEFAULT_ORIENTATION] = orientation
+        }
+    }
+
+    suspend fun setDefaultRulerLength(length: Float) {
+        context.dataStore.edit { prefs ->
+            prefs[KEY_DEFAULT_RULER_LENGTH] = length
+        }
+    }
+}

app/src/main/java/com/example/androidruler/theme/Theme.kt

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+package com.example.androidruler.theme
+
+import android.app.Activity
+import androidx.compose.foundation.isSystemInDarkTheme
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.darkColorScheme
+import androidx.compose.material3.lightColorScheme
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.SideEffect
+import androidx.compose.ui.graphics.toArgb
+import androidx.compose.ui.platform.LocalView
+import androidx.core.view.WindowCompat
+
+private val LightColorScheme = lightColorScheme()
+
+private val DarkColorScheme = darkColorScheme()
+
+@Composable
+fun AndroidRulerTheme(
+    darkTheme: Boolean = isSystemInDarkTheme(),
+    content: @Composable () -> Unit
+) {
+    val colorScheme = if (darkTheme) DarkColorScheme else LightColorScheme
+
+    val view = LocalView.current
+    if (!view.isInEditMode) {
+        SideEffect {
+            val window = (view.context as Activity).window
+            window.statusBarColor = colorScheme.primary.toArgb()
+            WindowCompat.getInsetsController(window, view).isAppearanceLightStatusBars = !darkTheme
+        }
+    }
+
+    MaterialTheme(
+        colorScheme = colorScheme,
+        content = content
+    )
+}

app/src/main/java/com/example/androidruler/ui/ControlBar.kt

@@ -0,0 +1,35 @@
+package com.example.androidruler.ui
+
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.filled.CameraAlt
+import androidx.compose.material.icons.filled.Straighten
+import androidx.compose.material3.Icon
+import androidx.compose.material3.NavigationBar
+import androidx.compose.material3.NavigationBarItem
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Modifier
+import com.example.androidruler.viewmodel.Mode
+
+@Composable
+fun ControlBar(
+    currentMode: Mode,
+    onModeChange: (Mode) -> Unit,
+    modifier: Modifier = Modifier
+) {
+    NavigationBar(modifier = modifier.fillMaxWidth()) {
+        NavigationBarItem(
+            selected = currentMode == Mode.RULER,
+            onClick = { onModeChange(Mode.RULER) },
+            icon = { Icon(Icons.Default.Straighten, contentDescription = "标尺") },
+            label = { Text("标尺") }
+        )
+        NavigationBarItem(
+            selected = currentMode == Mode.PHOTO,
+            onClick = { onModeChange(Mode.PHOTO) },
+            icon = { Icon(Icons.Default.CameraAlt, contentDescription = "拍照") },
+            label = { Text("拍照") }
+        )
+    }
+}

app/src/main/java/com/example/androidruler/ui/Markers.kt

@@ -0,0 +1,147 @@
+package com.example.androidruler.ui
+
+import androidx.compose.foundation.Canvas
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.offset
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.shape.CircleShape
+import androidx.compose.material3.Surface
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.geometry.Offset
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.graphics.PathEffect
+import androidx.compose.ui.platform.LocalConfiguration
+import androidx.compose.ui.platform.LocalDensity
+import androidx.compose.ui.unit.IntOffset
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
+import kotlin.math.roundToInt
+
+@Composable
+fun MarkerLayer(
+    pixelPerCm: Float,
+    scrollOffset: Float,
+    markStartCm: Float?,
+    markEndCm: Float?,
+    measuredDistance: Float?,
+    modifier: Modifier = Modifier
+) {
+    val density = LocalDensity.current
+    val isPortrait = LocalConfiguration.current.screenHeightDp > LocalConfiguration.current.screenWidthDp
+
+    Box(modifier = modifier.fillMaxSize()) {
+        markStartCm?.let { cm ->
+            val pos = cm * pixelPerCm - scrollOffset
+            MarkerDot(
+                color = Color(0xFF4CAF50),
+                position = pos,
+                isVertical = isPortrait,
+                density = density
+            )
+        }
+
+        markEndCm?.let { cm ->
+            val pos = cm * pixelPerCm - scrollOffset
+            MarkerDot(
+                color = Color(0xFFF44336),
+                position = pos,
+                isVertical = isPortrait,
+                density = density
+            )
+        }
+
+        if (markStartCm != null && markEndCm != null) {
+            val startPos = markStartCm * pixelPerCm - scrollOffset
+            val endPos = markEndCm * pixelPerCm - scrollOffset
+            measuredDistance?.let { dist ->
+                DashedConnection(
+                    start = startPos,
+                    end = endPos,
+                    isVertical = isPortrait,
+                    distance = dist,
+                    density = density
+                )
+            }
+        }
+    }
+}
+
+@Composable
+private fun MarkerDot(
+    color: Color,
+    position: Float,
+    isVertical: Boolean,
+    density: androidx.compose.ui.unit.Density
+) {
+    val px = with(density) { position.toDp().roundToPx() }
+    Surface(
+        modifier = Modifier
+            .then(
+                if (isVertical) Modifier.offset { IntOffset(0, px) }
+                else Modifier.offset { IntOffset(px, 0) }
+            )
+            .size(12.dp),
+        shape = CircleShape,
+        color = color
+    ) {}
+}
+
+@Composable
+private fun DashedConnection(
+    start: Float,
+    end: Float,
+    isVertical: Boolean,
+    distance: Float,
+    density: androidx.compose.ui.unit.Density
+) {
+    val startPos = minOf(start, end)
+    val endPos = maxOf(start, end)
+    val midPos = (startPos + endPos) / 2f
+
+    Box(modifier = Modifier.fillMaxSize()) {
+        Canvas(modifier = Modifier.fillMaxSize()) {
+            val space = 10f
+            val dashEffect = PathEffect.dashPathEffect(floatArrayOf(space, space), 0f)
+
+            if (isVertical) {
+                val x = size.width * 0.3f
+                drawLine(
+                    color = Color.Blue,
+                    start = Offset(x, startPos),
+                    end = Offset(x, endPos),
+                    strokeWidth = 2f,
+                    pathEffect = dashEffect
+                )
+            } else {
+                val y = size.height * 0.7f
+                drawLine(
+                    color = Color.Blue,
+                    start = Offset(startPos, y),
+                    end = Offset(endPos, y),
+                    strokeWidth = 2f,
+                    pathEffect = dashEffect
+                )
+            }
+        }
+
+        val midPx = with(density) { midPos.toDp().roundToPx() }
+        val offsetPx = with(density) { 80.dp.roundToPx() }
+
+        Text(
+            text = "${"%.1f".format(distance)} cm",
+            fontSize = 14.sp,
+            color = Color.Blue,
+            modifier = Modifier
+                .then(
+                    if (isVertical) {
+                        Modifier.offset { IntOffset(offsetPx, midPx) }
+                    } else {
+                        Modifier.offset { IntOffset(midPx, offsetPx) }
+                    }
+                )
+        )
+    }
+}

app/src/main/java/com/example/androidruler/ui/RulerCanvas.kt

@@ -0,0 +1,128 @@
+package com.example.androidruler.ui
+
+import androidx.compose.foundation.Canvas
+import androidx.compose.foundation.gestures.detectTapGestures
+import androidx.compose.foundation.horizontalScroll
+import androidx.compose.foundation.layout.fillMaxHeight
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.rememberScrollState
+import androidx.compose.foundation.verticalScroll
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.geometry.Offset
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.graphics.drawscope.DrawScope
+import androidx.compose.ui.input.pointer.pointerInput
+import androidx.compose.ui.platform.LocalConfiguration
+import androidx.compose.ui.text.TextMeasurer
+import androidx.compose.ui.text.TextStyle
+import androidx.compose.ui.text.drawText
+import androidx.compose.ui.text.rememberTextMeasurer
+import androidx.compose.ui.unit.sp
+import kotlin.math.roundToInt
+
+@Composable
+fun RulerCanvas(
+    pixelPerCm: Float,
+    scrollOffset: Float,
+    onTapCm: (Float) -> Unit,
+    modifier: Modifier = Modifier
+) {
+    val textMeasurer = rememberTextMeasurer()
+    val isPortrait = LocalConfiguration.current.screenHeightDp > LocalConfiguration.current.screenWidthDp
+
+    val scrollModifier = if (isPortrait) {
+        Modifier
+            .fillMaxWidth()
+            .verticalScroll(rememberScrollState())
+    } else {
+        Modifier
+            .fillMaxHeight()
+            .horizontalScroll(rememberScrollState())
+    }
+
+    Canvas(
+        modifier = modifier
+            .then(scrollModifier)
+            .pointerInput(Unit) {
+                detectTapGestures { offset ->
+                    val cm = if (isPortrait) {
+                        (offset.y + scrollOffset) / pixelPerCm
+                    } else {
+                        (offset.x + scrollOffset) / pixelPerCm
+                    }
+                    onTapCm(cm)
+                }
+            }
+    ) {
+        if (isPortrait) {
+            drawVerticalRuler(pixelPerCm, textMeasurer)
+        } else {
+            drawHorizontalRuler(pixelPerCm, textMeasurer)
+        }
+    }
+}
+
+private fun DrawScope.drawVerticalRuler(pixelPerCm: Float, textMeasurer: TextMeasurer) {
+    val totalCm = (size.height / pixelPerCm).roundToInt() + 1
+    val textColor = Color.Black
+
+    for (cm in 0..totalCm) {
+        val y = cm * pixelPerCm
+
+        for (mm in 1..9) {
+            val mmY = y + mm * (pixelPerCm / 10f)
+            val isHalf = mm == 5
+            val lineWidth = if (isHalf) size.width * 0.35f else size.width * 0.2f
+            drawLine(Color.Gray, Offset(size.width, mmY), Offset(size.width - lineWidth, mmY), 1f)
+        }
+
+        drawLine(textColor, Offset(size.width, y), Offset(size.width * 0.5f, y), 2f)
+
+        if (cm > 0) {
+            val textResult = textMeasurer.measure(
+                text = "$cm",
+                style = TextStyle(fontSize = 10.sp, color = textColor)
+            )
+            drawText(
+                textResult,
+                topLeft = Offset(
+                    size.width * 0.45f - textResult.size.width,
+                    y - textResult.size.height / 2f
+                )
+            )
+        }
+    }
+}
+
+private fun DrawScope.drawHorizontalRuler(pixelPerCm: Float, textMeasurer: TextMeasurer) {
+    val totalCm = (size.width / pixelPerCm).roundToInt() + 1
+    val textColor = Color.Black
+
+    for (cm in 0..totalCm) {
+        val x = cm * pixelPerCm
+
+        for (mm in 1..9) {
+            val mmX = x + mm * (pixelPerCm / 10f)
+            val isHalf = mm == 5
+            val lineHeight = if (isHalf) size.height * 0.35f else size.height * 0.2f
+            drawLine(Color.Gray, Offset(mmX, 0f), Offset(mmX, lineHeight), 1f)
+        }
+
+        drawLine(textColor, Offset(x, 0f), Offset(x, size.height * 0.5f), 2f)
+
+        if (cm > 0) {
+            val textResult = textMeasurer.measure(
+                text = "$cm",
+                style = TextStyle(fontSize = 10.sp, color = textColor)
+            )
+            drawText(
+                textResult,
+                topLeft = Offset(
+                    x - textResult.size.width / 2f,
+                    size.height * 0.5f + 2f
+                )
+            )
+        }
+    }
+}

app/src/main/java/com/example/androidruler/ui/RulerScreen.kt

@@ -0,0 +1,84 @@
+package com.example.androidruler.ui
+
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.padding
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.filled.Refresh
+import androidx.compose.material3.FloatingActionButton
+import androidx.compose.material3.Icon
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
+import com.example.androidruler.viewmodel.RulerViewModel
+
+@Composable
+fun RulerScreen(
+    viewModel: RulerViewModel,
+    modifier: Modifier = Modifier
+) {
+    val context = LocalContext.current
+
+    LaunchedEffect(Unit) {
+        val dpi = context.resources.displayMetrics.xdpi
+        viewModel.calculatePixelPerCm(dpi)
+    }
+
+    val measuredDistance = viewModel.measuredDistance
+
+    Box(modifier = modifier.fillMaxSize()) {
+        RulerCanvas(
+            pixelPerCm = viewModel.pixelPerCm,
+            scrollOffset = viewModel.scrollOffset,
+            onTapCm = { viewModel.setMark(it) },
+            modifier = Modifier.fillMaxSize()
+        )
+
+        MarkerLayer(
+            pixelPerCm = viewModel.pixelPerCm,
+            scrollOffset = viewModel.scrollOffset,
+            markStartCm = viewModel.markStartCm,
+            markEndCm = viewModel.markEndCm,
+            measuredDistance = measuredDistance,
+            modifier = Modifier.fillMaxSize()
+        )
+
+        measuredDistance?.let { dist ->
+            Text(
+                text = "${"%.1f".format(dist)} cm",
+                fontSize = 20.sp,
+                modifier = Modifier
+                    .align(Alignment.TopCenter)
+                    .padding(8.dp)
+            )
+        }
+
+        if (viewModel.markStartCm != null) {
+            FloatingActionButton(
+                onClick = { viewModel.resetMarks() },
+                modifier = Modifier
+                    .align(Alignment.BottomEnd)
+                    .padding(16.dp)
+            ) {
+                Icon(Icons.Default.Refresh, contentDescription = "重置")
+            }
+        }
+
+        if (!viewModel.isCalibrated) {
+            Text(
+                text = "建议先校准以获得更准确的测量结果",
+                fontSize = 12.sp,
+                color = Color(0xFFFF9800),
+                modifier = Modifier
+                    .align(Alignment.TopCenter)
+                    .padding(top = 36.dp)
+            )
+        }
+    }
+}

app/src/main/java/com/example/androidruler/ui/photo/CameraCapture.kt

@@ -0,0 +1,95 @@
+package com.example.androidruler.ui.photo
+
+import android.graphics.Bitmap
+import android.graphics.BitmapFactory
+import android.graphics.Matrix
+import androidx.camera.core.ImageCapture
+import androidx.camera.core.ImageCaptureException
+import androidx.camera.core.ImageProxy
+import androidx.camera.view.LifecycleCameraController
+import androidx.camera.view.PreviewView
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.shape.CircleShape
+import androidx.compose.material3.Button
+import androidx.compose.material3.ButtonDefaults
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.remember
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.platform.LocalLifecycleOwner
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.viewinterop.AndroidView
+import androidx.core.content.ContextCompat
+import java.nio.ByteBuffer
+import java.util.concurrent.Executors
+
+@Composable
+fun CameraCapture(
+    onPhotoTaken: (Bitmap) -> Unit,
+    modifier: Modifier = Modifier
+) {
+    val context = LocalContext.current
+    val lifecycleOwner = LocalLifecycleOwner.current
+
+    val cameraController = remember {
+        LifecycleCameraController(context).apply {
+            bindToLifecycle(lifecycleOwner)
+        }
+    }
+
+    Box(modifier = modifier.fillMaxSize()) {
+        AndroidView(
+            factory = { ctx ->
+                PreviewView(ctx).apply {
+                    controller = cameraController
+                }
+            },
+            modifier = Modifier.fillMaxSize()
+        )
+
+        Button(
+            onClick = {
+                cameraController.takePicture(
+                    ContextCompat.getMainExecutor(context),
+                    object : ImageCapture.OnImageCapturedCallback() {
+                        override fun onCaptureSuccess(image: ImageProxy) {
+                            val bitmap = imageProxyToBitmap(image)
+                            image.close()
+                            bitmap?.let { onPhotoTaken(it) }
+                        }
+
+                        override fun onError(exception: ImageCaptureException) {
+                            exception.printStackTrace()
+                        }
+                    }
+                )
+            },
+            modifier = Modifier
+                .align(Alignment.BottomCenter)
+                .padding(32.dp)
+                .size(72.dp),
+            shape = CircleShape,
+            colors = ButtonDefaults.buttonColors(containerColor = Color.White)
+        ) {
+            Text("拍")
+        }
+    }
+}
+
+private fun imageProxyToBitmap(image: ImageProxy): Bitmap? {
+    val buffer: ByteBuffer = image.planes[0].buffer
+    val bytes = ByteArray(buffer.remaining())
+    buffer.get(bytes)
+
+    val bitmap = BitmapFactory.decodeByteArray(bytes, 0, bytes.size) ?: return null
+    val matrix = Matrix().apply {
+        postRotate(image.imageInfo.rotationDegrees.toFloat())
+    }
+    return Bitmap.createBitmap(bitmap, 0, 0, bitmap.width, bitmap.height, matrix, true)
+}

app/src/main/java/com/example/androidruler/ui/photo/PhotoEditor.kt

@@ -0,0 +1,115 @@
+package com.example.androidruler.ui.photo
+
+import android.graphics.Bitmap
+import androidx.compose.foundation.Image
+import androidx.compose.foundation.gestures.detectTransformGestures
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.offset
+import androidx.compose.foundation.layout.padding
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.filled.Check
+import androidx.compose.material.icons.filled.Close
+import androidx.compose.material3.ButtonDefaults
+import androidx.compose.material3.FilledTonalButton
+import androidx.compose.material3.Icon
+import androidx.compose.material3.IconButton
+import androidx.compose.material3.OutlinedButton
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableFloatStateOf
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.geometry.Offset
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.graphics.asImageBitmap
+import androidx.compose.ui.graphics.graphicsLayer
+import androidx.compose.ui.input.pointer.pointerInput
+import androidx.compose.ui.layout.onSizeChanged
+import androidx.compose.ui.unit.IntOffset
+import androidx.compose.ui.unit.dp
+import kotlin.math.roundToInt
+
+@Composable
+fun PhotoEditor(
+    bitmap: Bitmap,
+    pixelPerCm: Float,
+    initialLength: Float,
+    onConfirm: (Bitmap) -> Unit,
+    onRetake: () -> Unit
+) {
+    var overlayLength by remember { mutableFloatStateOf(initialLength) }
+    var overlayPosition by remember { mutableStateOf(Offset(200f, 400f)) }
+    var overlayScale by remember { mutableFloatStateOf(1f) }
+    var overlayRotation by remember { mutableFloatStateOf(0f) }
+
+    Box(modifier = Modifier.fillMaxSize()) {
+        Image(
+            bitmap = bitmap.asImageBitmap(),
+            contentDescription = "照片",
+            modifier = Modifier.fillMaxSize()
+        )
+
+        Box(
+            modifier = Modifier
+                .offset { IntOffset(overlayPosition.x.roundToInt(), overlayPosition.y.roundToInt()) }
+                .graphicsLayer(
+                    scaleX = overlayScale,
+                    scaleY = overlayScale,
+                    rotationZ = overlayRotation
+                )
+                .pointerInput(Unit) {
+                    detectTransformGestures { _, pan, zoom, rotation ->
+                        overlayPosition = Offset(
+                            overlayPosition.x + pan.x,
+                            overlayPosition.y + pan.y
+                        )
+                        overlayScale *= zoom
+                        overlayRotation += rotation
+                    }
+                }
+        ) {
+            RulerOverlay(
+                lengthCm = overlayLength,
+                pixelPerCm = pixelPerCm
+            )
+        }
+
+        Row(
+            modifier = Modifier
+                .align(Alignment.TopEnd)
+                .padding(8.dp)
+        ) {
+            IconButton(onClick = onRetake) {
+                Icon(Icons.Default.Close, contentDescription = "重拍", tint = Color.White)
+            }
+        }
+
+        Row(
+            modifier = Modifier
+                .align(Alignment.BottomCenter)
+                .fillMaxWidth()
+                .padding(16.dp),
+            horizontalArrangement = Arrangement.SpaceEvenly
+        ) {
+            listOf(2f to "2cm", 5f to "5cm", 10f to "10cm").forEach { (len, label) ->
+                if (overlayLength == len) {
+                    FilledTonalButton(
+                        onClick = { overlayLength = len }
+                    ) { Text(label) }
+                } else {
+                    OutlinedButton(
+                        onClick = { overlayLength = len }
+                    ) { Text(label) }
+                }
+            }
+        }
+    }
+}

app/src/main/java/com/example/androidruler/ui/photo/PhotoMarkScreen.kt

@@ -0,0 +1,32 @@
+package com.example.androidruler.ui.photo
+
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Modifier
+import com.example.androidruler.viewmodel.RulerViewModel
+
+@Composable
+fun PhotoMarkScreen(
+    viewModel: RulerViewModel,
+    modifier: Modifier = Modifier
+) {
+    val photoBitmap = viewModel.photoBitmap
+
+    if (photoBitmap == null) {
+        CameraCapture(
+            onPhotoTaken = { bitmap ->
+                viewModel.photoBitmap = bitmap
+            },
+            modifier = modifier
+        )
+    } else {
+        PhotoEditor(
+            bitmap = photoBitmap,
+            pixelPerCm = viewModel.pixelPerCm,
+            initialLength = viewModel.overlayRulerLength,
+            onConfirm = { /* combined bitmap save handled later */ },
+            onRetake = {
+                viewModel.clearPhoto()
+            }
+        )
+    }
+}

app/src/main/java/com/example/androidruler/ui/photo/RulerOverlay.kt

@@ -0,0 +1,48 @@
+package com.example.androidruler.ui.photo
+
+import androidx.compose.foundation.Canvas
+import androidx.compose.foundation.layout.size
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.geometry.Offset
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.graphics.drawscope.DrawScope
+import androidx.compose.ui.platform.LocalDensity
+import androidx.compose.ui.unit.Dp
+import androidx.compose.ui.unit.dp
+
+@Composable
+fun RulerOverlay(
+    lengthCm: Float,
+    pixelPerCm: Float,
+    modifier: Modifier = Modifier
+) {
+    val widthDp: Dp = with(LocalDensity.current) {
+        (lengthCm * pixelPerCm).toDp()
+    }
+
+    Canvas(modifier = modifier.size(width = widthDp, height = 40.dp)) {
+        drawRuler(lengthCm, pixelPerCm)
+    }
+}
+
+private fun DrawScope.drawRuler(lengthCm: Float, pixelPerCm: Float) {
+    val totalPx = lengthCm * pixelPerCm
+
+    drawLine(Color.White, Offset(0f, 5f), Offset(totalPx, 5f), 30f)
+    drawLine(Color.Black, Offset(0f, 5f), Offset(totalPx, 5f), 2f)
+
+    val totalCm = lengthCm.toInt()
+    for (cm in 0..totalCm) {
+        val x = cm * pixelPerCm
+        drawLine(Color.Black, Offset(x, 0f), Offset(x, 20f), 2f)
+    }
+
+    for (mm in 1 until (lengthCm * 10).toInt()) {
+        val cm = mm / 10
+        val subMm = mm % 10
+        val x = cm * pixelPerCm + subMm * (pixelPerCm / 10f)
+        val lineHeight = if (subMm == 5) 12f else 8f
+        drawLine(Color.Gray, Offset(x, 8f), Offset(x, 8f + lineHeight), 1f)
+    }
+}

app/src/main/java/com/example/androidruler/ui/settings/CalibrationScreen.kt

@@ -0,0 +1,94 @@
+package com.example.androidruler.ui.settings
+
+import androidx.compose.foundation.Canvas
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
+import androidx.compose.material3.Button
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Slider
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableFloatStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.geometry.Offset
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
+
+@Composable
+fun CalibrationScreen(
+    initialFactor: Float,
+    onSave: (Float) -> Unit,
+    onBack: () -> Unit
+) {
+    val context = LocalContext.current
+    val dpi = context.resources.displayMetrics.xdpi
+    val rawPixelPerCm = dpi / 2.54f
+
+    var correctionFactor by remember { mutableFloatStateOf(initialFactor) }
+
+    val displayPixels = rawPixelPerCm * correctionFactor * 10f
+
+    Column(
+        modifier = Modifier
+            .fillMaxSize()
+            .padding(16.dp),
+        horizontalAlignment = Alignment.CenterHorizontally
+    ) {
+        Text(
+            text = "标尺校准",
+            style = MaterialTheme.typography.headlineMedium
+        )
+
+        Spacer(modifier = Modifier.height(8.dp))
+
+        Text(
+            text = "请拿一把真实的尺子，将屏幕上的 10cm 标记与尺子对齐",
+            fontSize = 14.sp,
+            color = Color.Gray
+        )
+
+        Spacer(modifier = Modifier.height(24.dp))
+
+        Canvas(modifier = Modifier.fillMaxWidth().height(60.dp)) {
+            val totalPx = displayPixels
+            drawLine(Color.Red, Offset(40f, 10f), Offset(40f, 50f), 3f)
+            drawLine(Color.Blue, Offset(40f + totalPx, 10f), Offset(40f + totalPx, 50f), 3f)
+            drawLine(Color.Black, Offset(40f, 30f), Offset(40f + totalPx, 30f), 2f)
+
+            for (cm in 1..10) {
+                val x = 40f + cm * (totalPx / 10f)
+                drawLine(Color.Black, Offset(x, 20f), Offset(x, 40f), 1.5f)
+            }
+        }
+
+        Spacer(modifier = Modifier.height(16.dp))
+
+        Text(text = "校正系数: ${"%.2f".format(correctionFactor)}")
+
+        Slider(
+            value = correctionFactor,
+            onValueChange = { correctionFactor = it },
+            valueRange = 0.5f..2.0f
+        )
+
+        Spacer(modifier = Modifier.height(24.dp))
+
+        Button(onClick = { onSave(correctionFactor) }) {
+            Text("保存校准")
+        }
+
+        Button(onClick = onBack) {
+            Text("返回")
+        }
+    }
+}

app/src/main/java/com/example/androidruler/ui/settings/SettingsScreen.kt

@@ -0,0 +1,151 @@
+package com.example.androidruler.ui.settings
+
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.filled.ArrowBack
+import androidx.compose.material3.Divider
+import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.material3.Icon
+import androidx.compose.material3.IconButton
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.RadioButton
+import androidx.compose.material3.Scaffold
+import androidx.compose.material3.Text
+import androidx.compose.material3.TopAppBar
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableFloatStateOf
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.unit.dp
+
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+fun SettingsScreen(
+    currentOrientation: String,
+    currentRulerLength: Float,
+    correctionFactor: Float,
+    onBack: () -> Unit,
+    onSave: (String, Float, Float) -> Unit
+) {
+    var showCalibration by remember { mutableStateOf(false) }
+    var selectedOrientation by remember { mutableStateOf(currentOrientation) }
+    var selectedLength by remember { mutableFloatStateOf(currentRulerLength) }
+
+    if (showCalibration) {
+        CalibrationScreen(
+            initialFactor = correctionFactor,
+            onSave = { factor ->
+                onSave(selectedOrientation, selectedLength, factor)
+                showCalibration = false
+            },
+            onBack = { showCalibration = false }
+        )
+    } else {
+        Scaffold(
+            topBar = {
+                TopAppBar(
+                    title = { Text("设置") },
+                    navigationIcon = {
+                        IconButton(onClick = onBack) {
+                            Icon(Icons.Default.ArrowBack, contentDescription = "返回")
+                        }
+                    }
+                )
+            }
+        ) { padding ->
+            Column(
+                modifier = Modifier
+                    .fillMaxSize()
+                    .padding(padding)
+                    .padding(16.dp)
+            ) {
+                Text(
+                    text = "标尺校准",
+                    style = MaterialTheme.typography.titleMedium
+                )
+                Text(
+                    text = "当前校正系数: ${"%.2f".format(correctionFactor)}",
+                    color = MaterialTheme.colorScheme.secondary
+                )
+                Text(
+                    text = "点击进入校准",
+                    color = MaterialTheme.colorScheme.primary,
+                    modifier = Modifier
+                        .clickable { showCalibration = true }
+                        .padding(vertical = 8.dp)
+                )
+
+                Divider(modifier = Modifier.padding(vertical = 16.dp))
+
+                Text(
+                    text = "默认方向",
+                    style = MaterialTheme.typography.titleMedium
+                )
+                Row(
+                    verticalAlignment = Alignment.CenterVertically,
+                    modifier = Modifier.fillMaxWidth()
+                ) {
+                    listOf("竖屏" to "portrait", "横屏" to "landscape", "自适应" to "auto").forEach { (label, value) ->
+                        Row(
+                            verticalAlignment = Alignment.CenterVertically,
+                            modifier = Modifier
+                                .clickable { selectedOrientation = value }
+                                .padding(end = 16.dp, top = 4.dp)
+                        ) {
+                            RadioButton(
+                                selected = selectedOrientation == value,
+                                onClick = { selectedOrientation = value }
+                            )
+                            Text(text = label)
+                        }
+                    }
+                }
+
+                Divider(modifier = Modifier.padding(vertical = 16.dp))
+
+                Text(
+                    text = "拍照标尺默认长度",
+                    style = MaterialTheme.typography.titleMedium
+                )
+                Row(
+                    verticalAlignment = Alignment.CenterVertically,
+                    modifier = Modifier.fillMaxWidth()
+                ) {
+                    listOf(2f to "2cm", 5f to "5cm", 10f to "10cm").forEach { (length, label) ->
+                        Row(
+                            verticalAlignment = Alignment.CenterVertically,
+                            modifier = Modifier
+                                .clickable { selectedLength = length }
+                                .padding(end = 16.dp, top = 4.dp)
+                        ) {
+                            RadioButton(
+                                selected = selectedLength == length,
+                                onClick = { selectedLength = length }
+                            )
+                            Text(text = label)
+                        }
+                    }
+                }
+
+                Spacer(modifier = Modifier.height(24.dp))
+
+                Text(
+                    text = "关于",
+                    style = MaterialTheme.typography.titleMedium
+                )
+                Text(text = "标尺 v1.0", color = MaterialTheme.colorScheme.secondary)
+            }
+        }
+    }
+}

app/src/main/java/com/example/androidruler/ui/util/ImageSaver.kt

@@ -0,0 +1,48 @@
+package com.example.androidruler.ui.util
+
+import android.content.ContentValues
+import android.content.Context
+import android.graphics.Bitmap
+import android.os.Build
+import android.os.Environment
+import android.provider.MediaStore
+import java.io.File
+import java.io.FileOutputStream
+
+object ImageSaver {
+
+    fun save(context: Context, bitmap: Bitmap): Boolean {
+        return try {
+            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
+                val values = ContentValues().apply {
+                    put(MediaStore.Images.Media.DISPLAY_NAME, "ruler_${System.currentTimeMillis()}.jpg")
+                    put(MediaStore.Images.Media.MIME_TYPE, "image/jpeg")
+                    put(MediaStore.Images.Media.RELATIVE_PATH, Environment.DIRECTORY_PICTURES + "/Ruler")
+                }
+                val uri = context.contentResolver.insert(
+                    MediaStore.Images.Media.EXTERNAL_CONTENT_URI,
+                    values
+                )
+                uri?.let {
+                    context.contentResolver.openOutputStream(it)?.use { out ->
+                        bitmap.compress(Bitmap.CompressFormat.JPEG, 95, out)
+                    }
+                }
+            } else {
+                val dir = File(
+                    Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES),
+                    "Ruler"
+                )
+                dir.mkdirs()
+                val file = File(dir, "ruler_${System.currentTimeMillis()}.jpg")
+                FileOutputStream(file).use { out ->
+                    bitmap.compress(Bitmap.CompressFormat.JPEG, 95, out)
+                }
+            }
+            true
+        } catch (e: Exception) {
+            e.printStackTrace()
+            false
+        }
+    }
+}

app/src/main/java/com/example/androidruler/viewmodel/RulerViewModel.kt

@@ -0,0 +1,93 @@
+package com.example.androidruler.viewmodel
+
+import android.app.Application
+import android.graphics.Bitmap
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableFloatStateOf
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.setValue
+import androidx.lifecycle.AndroidViewModel
+import androidx.lifecycle.viewModelScope
+import com.example.androidruler.data.SettingsRepository
+import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.launch
+import kotlin.math.abs
+
+enum class Mode { RULER, PHOTO }
+
+class RulerViewModel(application: Application) : AndroidViewModel(application) {
+
+    private val repo = SettingsRepository(application)
+
+    var mode by mutableStateOf(Mode.RULER)
+    var showSettings by mutableStateOf(false)
+
+    var pixelPerCm by mutableFloatStateOf(0f)
+    var scrollOffset by mutableFloatStateOf(0f)
+    var markStartCm: Float? by mutableStateOf(null)
+    var markEndCm: Float? by mutableStateOf(null)
+
+    var photoBitmap: Bitmap? by mutableStateOf(null)
+    var overlayRulerLength by mutableFloatStateOf(3.0f)
+
+    var cmCorrectionFactor by mutableFloatStateOf(1.0f)
+    var defaultOrientation by mutableStateOf("auto")
+    var isCalibrated by mutableStateOf(false)
+
+    init {
+        viewModelScope.launch {
+            cmCorrectionFactor = repo.correctionFactor.first()
+            isCalibrated = repo.isCalibrated.first()
+            defaultOrientation = repo.defaultOrientation.first()
+            overlayRulerLength = repo.defaultRulerLength.first()
+        }
+    }
+
+    fun calculatePixelPerCm(dpi: Float) {
+        val rawPixelPerCm = dpi / 2.54f
+        pixelPerCm = rawPixelPerCm * cmCorrectionFactor
+    }
+
+    fun resetMarks() {
+        markStartCm = null
+        markEndCm = null
+    }
+
+    fun setMark(cm: Float) {
+        if (markStartCm == null) {
+            markStartCm = cm
+        } else if (markEndCm == null) {
+            markEndCm = cm
+        } else {
+            markStartCm = cm
+            markEndCm = null
+        }
+    }
+
+    val measuredDistance: Float?
+        get() {
+            val s = markStartCm
+            val e = markEndCm
+            return if (s != null && e != null) abs(e - s) else null
+        }
+
+    fun updateSettings(
+        orientation: String,
+        rulerLength: Float,
+        correctionFactor: Float
+    ) {
+        viewModelScope.launch {
+            defaultOrientation = orientation
+            overlayRulerLength = rulerLength
+            cmCorrectionFactor = correctionFactor
+            repo.setDefaultOrientation(orientation)
+            repo.setDefaultRulerLength(rulerLength)
+            repo.setCorrectionFactor(correctionFactor)
+            isCalibrated = true
+        }
+    }
+
+    fun clearPhoto() {
+        photoBitmap = null
+    }
+}

app/src/main/res/values/strings.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <string name="app_name">标尺</string>
+</resources>

app/src/main/res/values/themes.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <style name="Theme.AndroidRuler" parent="android:Theme.Material.Light.NoActionBar" />
+</resources>

app/src/main/res/xml/backup_rules.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<full-backup-content>
+    <include domain="sharedpref" path="." />
+</full-backup-content>