Fix: resolve 5 bugs found during project onboarding health check

- custom_inference_worker: reuse existing device_group from DeviceController
  to avoid double kp.connect_devices() conflict on same USB port
- custom_inference_worker: add TYPE_CHECKING guard for kp type annotations
  to prevent potential NameError at import time
- utilities_screen: replace missing back_arrow.png with text arrow (←)
- utilities_screen: add set_device_controller() so AppController can inject
  MainWindow's shared DeviceController instance
- main.py: wire UtilitiesScreen to share MainWindow's DeviceController
- video_thread: emit camera_error_signal on failure and max-retry exhaustion
- media_controller: connect camera_error_signal and display error on canvas
- media_panel: fix pause button using wrong delete icon; use video_normal SVG

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

main.py

@@ -67,6 +67,10 @@ class AppController:
         self.main_window = MainWindow()
         self.stack.addWidget(self.main_window)
 
+        # Share MainWindow's DeviceController with UtilitiesScreen so both
+        # screens reflect the same device connection state.
+        self.utilities_screen.set_device_controller(self.main_window.device_controller)
+    
     def connect_signals(self):
         """
         Connect signals between screens for navigation.

src/controllers/inference_controller.py

@@ -11,7 +11,6 @@ import cv2
 import json
 from PyQt5.QtWidgets import QMessageBox, QApplication
 from PyQt5.QtCore import QTimer, Qt
-import kp
 
 from src.models.inference_worker import InferenceWorkerThread
 from src.models.custom_inference_worker import CustomInferenceWorkerThread
@@ -187,6 +186,7 @@ class InferenceController:
                 # Upload model to device
                 if device_group:
                     try:
+                        import kp
                         print('[Uploading model]')
                         self.model_descriptor = kp.core.load_model_from_file(
                             device_group=device_group,
@@ -364,6 +364,9 @@ class InferenceController:
             input_params["custom_ncpu_path"] = tool_config.get("custom_ncpu_path")
             input_params["custom_labels"] = tool_config.get("custom_labels")
 
+            # Pass existing device_group to avoid double connection in the worker
+            input_params["device_group"] = self.device_controller.get_device_group()
+
             # Get device-related settings
             selected_device = self.device_controller.get_selected_device()
             if selected_device:

src/controllers/media_controller.py

@@ -66,6 +66,7 @@ class MediaController:
                         print("Camera signal connected successfully")
                     except Exception as e:
                         print(f"Error connecting camera signal: {e}")
+                self.video_thread.camera_error_signal.connect(self.handle_camera_error)
 
                 # Start camera thread
                 self.video_thread.start()
@@ -163,6 +164,20 @@ class MediaController:
             import traceback
             print(traceback.format_exc())
     
+    def handle_camera_error(self, error_msg):
+        """
+        Handle camera error signal from VideoThread.
+
+        Args:
+            error_msg (str): Error message describing what went wrong.
+        """
+        print(f"Camera error: {error_msg}")
+        if hasattr(self.main_window, 'canvas_label'):
+            self.main_window.canvas_label.setText(error_msg)
+            self.main_window.canvas_label.setAlignment(Qt.AlignCenter)
+        self.video_thread = None
+        self._signal_was_connected = False
+
     def reconnect_camera_signal(self):
         """Reconnect the camera signal if it was previously disconnected"""
         if self.video_thread is not None and self._signal_was_connected:

src/models/custom_inference_worker.py

@@ -4,16 +4,17 @@ custom_inference_worker.py - Custom Inference Worker
 This module provides a worker thread for running inference using user-uploaded
 custom models. It uses YOLO V5 pre/post-processing logic for object detection.
 """
+from __future__ import annotations
 import os
 import time
 import queue
 import cv2
 import numpy as np
-from typing import List
+from typing import List, TYPE_CHECKING
 from PyQt5.QtCore import QThread, pyqtSignal
 
-import kp
+if TYPE_CHECKING:
-from kp.KPBaseClass.ValueBase import ValueRepresentBase
+    import kp
 
 
 # COCO dataset class names (80 classes)
@@ -31,7 +32,7 @@ COCO_CLASSES = [
 ]
 
 
-class ExampleBoundingBox(ValueRepresentBase):
+class ExampleBoundingBox:
     """Bounding box descriptor."""
 
     def __init__(self,
@@ -59,7 +60,7 @@ class ExampleBoundingBox(ValueRepresentBase):
         }
 
 
-class ExampleYoloResult(ValueRepresentBase):
+class ExampleYoloResult:
     """YOLO output result descriptor."""
 
     def __init__(self,
@@ -354,6 +355,10 @@ class CustomInferenceWorkerThread(QThread):
         """
         Initialize device, upload firmware and model.
 
+        If a device_group is already provided in input_params (connected by
+        DeviceController), reuse it and skip connect_devices to avoid double
+        connection conflicts with the Kneron SDK.
+
         Returns:
             bool: True if initialization successful, False otherwise.
         """
@@ -374,11 +379,19 @@ class CustomInferenceWorkerThread(QThread):
                 print("Missing required file paths")
                 return False
 
-            # Connect to device
+            import kp
-            print('[Connecting device]')
+
-            self.device_group = kp.core.connect_devices(usb_port_ids=[port_id])
+            # Reuse existing device_group if provided to avoid double connection
+            existing_device_group = self.input_params.get("device_group")
+            if existing_device_group is not None:
+                print('[Reusing existing device connection]')
+                self.device_group = existing_device_group
+            else:
+                print('[Connecting device]')
+                self.device_group = kp.core.connect_devices(usb_port_ids=[port_id])
+                print(' - Connection successful')
+
             kp.core.set_timeout(device_group=self.device_group, milliseconds=5000)
-            print(' - Connection successful')
 
             # Upload firmware
             print('[Uploading firmware]')
@@ -421,6 +434,7 @@ class CustomInferenceWorkerThread(QThread):
             img_processed, original_width, original_height = preprocess_frame(frame)
 
             # 建立推論描述符
+            import kp
             descriptor = kp.GenericImageInferenceDescriptor(
                 model_id=self.model_descriptor.models[0].id,
                 inference_number=0,
@@ -532,11 +546,20 @@ class CustomInferenceWorkerThread(QThread):
         self.quit()
 
     def cleanup(self):
-        """Clean up resources and disconnect device."""
+        """Clean up resources.
+
+        Only disconnects device if this worker created the connection itself
+        (i.e. no device_group was provided via input_params).
+        """
         try:
             if self.device_group is not None:
-                kp.core.disconnect_devices(self.device_group)
+                owned_by_worker = self.input_params.get("device_group") is None
-                print('[Device disconnected]')
+                if owned_by_worker:
+                    import kp
+                    kp.core.disconnect_devices(self.device_group)
+                    print('[Device disconnected]')
+                else:
+                    print('[Device connection owned by DeviceController, skipping disconnect]')
                 self.device_group = None
         except Exception as e:
             print(f"Error cleaning up resources: {e}")

src/models/video_thread.py

@@ -125,9 +125,10 @@ class VideoThread(QThread):
                     height, width, channel = frame.shape
                     bytes_per_line = channel * width
                     qt_image = QImage(frame.data, width, height, bytes_per_line, QImage.Format_RGB888)
-                    self.change_pixmap_signal.emit(qt_image)
+                    self.change_pixmap_signal.emit(qt_image.copy())
                 else:
                     print("Unable to read camera frame, camera may be disconnected")
+                    self.camera_error_signal.emit("相機連線中斷，嘗試重新連線...")
                     break
 
             # Release camera resources
@@ -141,6 +142,7 @@ class VideoThread(QThread):
 
         if self._camera_open_attempts >= self._max_attempts:
             print("Maximum attempts reached, unable to open camera")
+            self.camera_error_signal.emit("無法開啟相機，請確認相機是否連接")
 
     def stop(self):
         """Stop the video capture thread."""

src/views/components/media_panel.py

@@ -25,7 +25,7 @@ def create_media_panel(parent, media_controller, file_service):
              media_controller.take_screenshot),
             ('upload file', os.path.join(assets_path, "Assets_svg/bt_function_upload_normal.svg").replace('\\', '/'), 
              file_service.upload_file),
-            ('pause/resume', os.path.join(assets_path, "Assets_svg/btn_result_image_delete_hover.svg").replace('\\', '/'), 
+            ('pause/resume', os.path.join(assets_path, "Assets_svg/bt_function_video_normal.svg").replace('\\', '/'),
              lambda: toggle_pause_button(parent, media_controller)),
             ('voice', os.path.join(assets_path, "Assets_svg/ic_recording_voice.svg").replace('\\', '/'), 
              lambda: media_controller.record_audio(None)),

src/views/utilities_screen.py

@@ -14,7 +14,6 @@ from PyQt5.QtWidgets import (
 from PyQt5.QtCore import Qt, pyqtSignal, QTimer
 from PyQt5.QtGui import QPixmap, QFont, QIcon, QColor
 import os
-import kp
 from src.config import UXUI_ASSETS, WINDOW_SIZE, BACKGROUND_COLOR, DongleModelMap
 from src.controllers.device_controller import DeviceController
 from src.services.device_service import check_available_device
@@ -56,6 +55,18 @@ class UtilitiesScreen(QWidget):
         self.current_page = "utilities"  # Track current page: "utilities" or "purchased_items"
         self.init_ui()
 
+    def set_device_controller(self, device_controller):
+        """
+        Replace the local DeviceController with a shared instance.
+
+        Call this from AppController after all screens are created so that
+        UtilitiesScreen and MainWindow share the same device connection state.
+
+        Args:
+            device_controller: Shared DeviceController instance from MainWindow.
+        """
+        self.device_controller = device_controller
+        
     def init_ui(self):
         """
         Initialize the user interface.
@@ -135,14 +146,14 @@ class UtilitiesScreen(QWidget):
         header_layout.setContentsMargins(20, 0, 20, 0)
         
         # Back button
-        back_button = QPushButton("", self)
+        back_button = QPushButton("←", self)
-        back_button.setIcon(QIcon(os.path.join(UXUI_ASSETS, "Assets_png/back_arrow.png")))
-        back_button.setIconSize(QPixmap(os.path.join(UXUI_ASSETS, "Assets_png/back_arrow.png")).size())
         back_button.setFixedSize(40, 40)
         back_button.setStyleSheet("""
             QPushButton {
                 background-color: transparent;
                 border: none;
+                color: white;
+                font-size: 20px;
             }
             QPushButton:hover {
                 background-color: rgba(255, 255, 255, 0.1);
@@ -851,6 +862,7 @@ class UtilitiesScreen(QWidget):
                     firmware_version = "-"
                     try:
                         if device.is_connectable:
+                            import kp
                             # Connect to device and get system info
                             device_group = kp.core.connect_devices(usb_port_ids=[port_id])
                             system_info = kp.core.get_system_info(
@@ -980,6 +992,7 @@ class UtilitiesScreen(QWidget):
             self.show_progress(f"Updating firmware for {device_model}...", 0)
 
             # Connect to device
+            import kp
             device_group = kp.core.connect_devices(usb_port_ids=[int(port_id)])
 
             # Build firmware file paths
@@ -1026,6 +1039,7 @@ class UtilitiesScreen(QWidget):
             self.show_progress("Installing Kneron Device Drivers...", 0)
 
             # List all product IDs
+            import kp
             product_ids = [
                 kp.ProductId.KP_DEVICE_KL520,
                 kp.ProductId.KP_DEVICE_KL720_LEGACY,