fix: improve ui.py code quality

temp_file_trans_client/ui.py

@@ -1,10 +1,11 @@
 from PySide6.QtWidgets import (QWidget, QVBoxLayout, QHBoxLayout, 
                                QLineEdit, QPushButton, QLabel, QComboBox,
-                               QProgressBar, QTextEdit, QFrame)
-from PySide6.QtCore import Qt, QRect
-from PySide6.QtGui import QPixmap, QPainter, QPen, QColor, QBrush
+                               QProgressBar, QTextEdit, QFrame, QFileDialog)
+from PySide6.QtCore import Qt, Signal
 
 class DropZone(QFrame):
+    file_dropped = Signal(str)
+    
     def __init__(self, parent=None):
         super().__init__(parent)
         self.setAcceptDrops(True)
@@ -48,14 +49,13 @@ class DropZone(QFrame):
             if urls:
                 self.file_selected = urls[0].toLocalFile()
                 event.acceptProposedAction()
-                self.parent().on_file_selected(self.file_selected)
+                self.file_dropped.emit(self.file_selected)
     
     def mousePressEvent(self, event):
-        from PySide6.QtWidgets import QFileDialog
         filepath, _ = QFileDialog.getOpenFileName(self, "选择文件")
         if filepath:
             self.file_selected = filepath
-            self.parent().on_file_selected(filepath)
+            self.file_dropped.emit(filepath)
 
 class UiCreator:
     @staticmethod