Merge pull request #994 from fumin65/pause_function

feat: add pause feature

@@ -273,7 +273,7 @@ class MobileScanner(
             }
 
             cameraProvider?.unbindAll()
-            textureEntry = textureRegistry.createSurfaceTexture()
+            textureEntry = textureEntry ?: textureRegistry.createSurfaceTexture()
 
             // Preview
             val surfaceProvider = Preview.SurfaceProvider { request ->
@@ -405,14 +405,33 @@ class MobileScanner(
         }, executor)
 
     }
+
+    /**
+     * Pause barcode scanning.
+     */
+    fun pause() {
+        if (isPaused()) {
+            throw AlreadyPaused()
+        } else if (isStopped()) {
+            throw AlreadyStopped()
+        }
+
+        releaseCamera()
+    }
+
     /**
      * Stop barcode scanning.
      */
     fun stop() {
-        if (isStopped()) {
+        if (!isPaused() && isStopped()) {
             throw AlreadyStopped()
         }
 
+        releaseCamera()
+        releaseTexture()
+    }
+
+    private fun releaseCamera() {
         if (displayListener != null) {
             val displayManager = activity.applicationContext.getSystemService(Context.DISPLAY_SERVICE) as DisplayManager
 
@@ -430,9 +449,6 @@ class MobileScanner(
         // Unbind the camera use cases, the preview is a use case.
         // The camera will be closed when the last use case is unbound.
         cameraProvider?.unbindAll()
-        cameraProvider = null
-        camera = null
-        preview = null
 
         // Release the texture for the preview.
         textureEntry?.release()
@@ -444,7 +460,13 @@ class MobileScanner(
         lastScanned = null
     }
 
+    private fun releaseTexture() {
+        textureEntry?.release()
+        textureEntry = null
+    }
+
     private fun isStopped() = camera == null && preview == null
+    private fun isPaused() = isStopped() && textureEntry != null
 
     /**
      * Toggles the flash light on or off.

@@ -3,6 +3,7 @@ package dev.steenbakker.mobile_scanner
 class NoCamera : Exception()
 class AlreadyStarted : Exception()
 class AlreadyStopped : Exception()
+class AlreadyPaused : Exception()
 class CameraError : Exception()
 class ZoomWhenStopped : Exception()
 class ZoomNotInRange : Exception()
\ No newline at end of file

@@ -118,6 +118,7 @@ class MobileScannerHandler(
                     }
                 })
             "start" -> start(call, result)
+            "pause" -> pause(result)
             "stop" -> stop(result)
             "toggleTorch" -> toggleTorch(result)
             "analyzeImage" -> analyzeImage(call, result)
@@ -213,6 +214,18 @@ class MobileScannerHandler(
         )
     }
 
+    private fun pause(result: MethodChannel.Result) {
+        try {
+            mobileScanner!!.pause()
+            result.success(null)
+        } catch (e: Exception) {
+            when (e) {
+                is AlreadyPaused, is AlreadyStopped -> result.success(null)
+                else -> throw e
+            }
+        }
+    }
+
     private fun stop(result: MethodChannel.Result) {
         try {
             mobileScanner!!.stop()

@@ -105,6 +105,7 @@ class _BarcodeScannerWithControllerState
                 children: [
                   ToggleFlashlightButton(controller: controller),
                   StartStopMobileScannerButton(controller: controller),
+                  PauseMobileScannerButton(controller: controller),
                   Expanded(child: Center(child: _buildBarcode(_barcode))),
                   SwitchCameraButton(controller: controller),
                   AnalyzeImageFromGalleryButton(controller: controller),

@@ -180,3 +180,30 @@ class ToggleFlashlightButton extends StatelessWidget {
     );
   }
 }
+
+class PauseMobileScannerButton extends StatelessWidget {
+  const PauseMobileScannerButton({required this.controller, super.key});
+
+  final MobileScannerController controller;
+
+  @override
+  Widget build(BuildContext context) {
+    return ValueListenableBuilder(
+      valueListenable: controller,
+      builder: (context, state, child) {
+        if (!state.isInitialized || !state.isRunning) {
+          return const SizedBox.shrink();
+        }
+
+        return IconButton(
+          color: Colors.white,
+          iconSize: 32.0,
+          icon: const Icon(Icons.pause),
+          onPressed: () async {
+            await controller.pause();
+          },
+        );
+      },
+    );
+  }
+}

@@ -58,6 +58,14 @@ public class MobileScanner: NSObject, AVCaptureVideoDataOutputSampleBufferDelega
     
     public var timeoutSeconds: Double = 0
 
+    private var stopped: Bool {
+        return device == nil || captureSession == nil
+    }
+
+    private var paused: Bool {
+        return stopped && textureId != nil
+    }
+
     init(registry: FlutterTextureRegistry?, mobileScannerCallback: @escaping MobileScannerCallback, torchModeChangeCallback: @escaping TorchModeChangeCallback, zoomScaleChangeCallback: @escaping ZoomScaleChangeCallback) {
         self.registry = registry
         self.mobileScannerCallback = mobileScannerCallback
@@ -123,6 +131,7 @@ public class MobileScanner: NSObject, AVCaptureVideoDataOutputSampleBufferDelega
     
     /// Gets called when a new image is added to the buffer
     public func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
+
         guard let imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer) else {
             return
         }
@@ -178,7 +187,7 @@ public class MobileScanner: NSObject, AVCaptureVideoDataOutputSampleBufferDelega
         barcodesString = nil
         scanner = barcodeScannerOptions != nil ? BarcodeScanner.barcodeScanner(options: barcodeScannerOptions!) : BarcodeScanner.barcodeScanner()
         captureSession = AVCaptureSession()
-        textureId = registry?.register(self)
+        textureId = textureId ?? registry?.register(self)
 
         // Open the camera device
         device = getDefaultCameraDevice(position: cameraPosition)
@@ -293,27 +302,49 @@ public class MobileScanner: NSObject, AVCaptureVideoDataOutputSampleBufferDelega
         }
     }
 
+    /// Pause scanning for barcodes
+    func pause() throws {
+        if (paused) {
+            throw MobileScannerError.alreadyPaused
+        } else if (stopped) {
+            throw MobileScannerError.alreadyStopped
+        }
+        releaseCamera()
+    }
+
     /// Stop scanning for barcodes
     func stop() throws {
-        if (device == nil || captureSession == nil) {
+        if (!paused && stopped) {
             throw MobileScannerError.alreadyStopped
         }
+        releaseCamera()
+        releaseTexture()
+    }
+
+    private func releaseCamera() {
+
+        guard let captureSession = captureSession else {
+            return
+        }
 
-        captureSession!.stopRunning()
-        for input in captureSession!.inputs {
-            captureSession!.removeInput(input)
+        captureSession.stopRunning()
+        for input in captureSession.inputs {
+            captureSession.removeInput(input)
         }
-        for output in captureSession!.outputs {
-            captureSession!.removeOutput(output)
+        for output in captureSession.outputs {
+            captureSession.removeOutput(output)
         }
 
         latestBuffer = nil
         device.removeObserver(self, forKeyPath: #keyPath(AVCaptureDevice.torchMode))
         device.removeObserver(self, forKeyPath: #keyPath(AVCaptureDevice.videoZoomFactor))
+        self.captureSession = nil
+        device = nil
+    }
+
+    private func releaseTexture() {
         registry?.unregisterTexture(textureId)
         textureId = nil
-        captureSession = nil
-        device = nil
         scanner = nil
     }
 

@@ -16,6 +16,7 @@ enum MobileScannerError: Error {
     case noCamera
     case alreadyStarted
     case alreadyStopped
+    case alreadyPaused
     case cameraError(_ error: Error)
     case zoomWhenStopped
     case zoomError(_ error: Error)

@@ -105,6 +105,8 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin {
             AVCaptureDevice.requestAccess(for: .video, completionHandler: { result($0) })
         case "start":
             start(call, result)
+        case "pause":
+            pause(result)
         case "stop":
             stop(result)
         case "toggleTorch":
@@ -167,6 +169,14 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin {
         }
     }
     
+    /// Stops the mobileScanner without closing the texture.
+    private func pause(_ result: @escaping FlutterResult) {
+        do {
+            try mobileScanner.pause()
+        } catch {}
+        result(nil)
+    }
+
     /// Stops the mobileScanner and closes the texture.
     private func stop(_ result: @escaping FlutterResult) {
         do {

@@ -46,6 +46,7 @@ class MethodChannelMobileScanner extends MobileScannerPlatform {
   }
 
   int? _textureId;
+  bool _pausing = false;
 
   /// Parse a [BarcodeCapture] from the given [event].
   BarcodeCapture? _parseBarcode(Map<Object?, Object?>? event) {
@@ -216,7 +217,7 @@ class MethodChannelMobileScanner extends MobileScannerPlatform {
 
   @override
   Future<MobileScannerViewAttributes> start(StartOptions startOptions) async {
-    if (_textureId != null) {
+    if (!_pausing && _textureId != null) {
       throw const MobileScannerException(
         errorCode: MobileScannerErrorCode.controllerAlreadyInitialized,
         errorDetails: MobileScannerErrorDetails(
@@ -281,6 +282,8 @@ class MethodChannelMobileScanner extends MobileScannerPlatform {
       size = Size.zero;
     }
 
+    _pausing = false;
+
     return MobileScannerViewAttributes(
       currentTorchMode: currentTorchState,
       numberOfCameras: numberOfCameras,
@@ -295,11 +298,23 @@ class MethodChannelMobileScanner extends MobileScannerPlatform {
     }
 
     _textureId = null;
+    _pausing = false;
 
     await methodChannel.invokeMethod<void>('stop');
   }
 
   @override
+  Future<void> pause() async {
+    if (_pausing) {
+      return;
+    }
+
+    _pausing = true;
+
+    await methodChannel.invokeMethod<void>('pause');
+  }
+
+  @override
   Future<void> toggleTorch() async {
     await methodChannel.invokeMethod<void>('toggleTorch');
   }

@@ -183,6 +183,30 @@ class MobileScannerController extends ValueNotifier<MobileScannerState> {
     }
   }
 
+  void _stop() {
+    // Do nothing if not initialized or already stopped.
+    // On the web, the permission popup triggers a lifecycle change from resumed to inactive,
+    // due to the permission popup gaining focus.
+    // This would 'stop' the camera while it is not ready yet.
+    if (!value.isInitialized || !value.isRunning || _isDisposed) {
+      return;
+    }
+
+    _disposeListeners();
+
+    final TorchState oldTorchState = value.torchState;
+
+    // After the camera stopped, set the torch state to off,
+    // as the torch state callback is never called when the camera is stopped.
+    // If the device does not have a torch, do not report "off".
+    value = value.copyWith(
+      isRunning: false,
+      torchState: oldTorchState == TorchState.unavailable
+          ? TorchState.unavailable
+          : TorchState.off,
+    );
+  }
+
   /// Analyze an image file.
   ///
   /// The [path] points to a file on the device.
@@ -336,29 +360,19 @@ class MobileScannerController extends ValueNotifier<MobileScannerState> {
   ///
   /// Does nothing if the camera is already stopped.
   Future<void> stop() async {
-    // Do nothing if not initialized or already stopped.
-    // On the web, the permission popup triggers a lifecycle change from resumed to inactive,
-    // due to the permission popup gaining focus.
-    // This would 'stop' the camera while it is not ready yet.
-    if (!value.isInitialized || !value.isRunning || _isDisposed) {
-      return;
+    _stop();
+    await MobileScannerPlatform.instance.stop();
   }
 
-    _disposeListeners();
-
-    final TorchState oldTorchState = value.torchState;
-
-    // After the camera stopped, set the torch state to off,
-    // as the torch state callback is never called when the camera is stopped.
-    // If the device does not have a torch, do not report "off".
-    value = value.copyWith(
-      isRunning: false,
-      torchState: oldTorchState == TorchState.unavailable
-          ? TorchState.unavailable
-          : TorchState.off,
-    );
-
-    await MobileScannerPlatform.instance.stop();
+  /// Pause the camera.
+  ///
+  /// This method stops to update camera frame and scan barcodes.
+  /// After calling this method, the camera can be restarted using [start].
+  ///
+  /// Does nothing if the camera is already paused or stopped.
+  Future<void> pause() async {
+    _stop();
+    await MobileScannerPlatform.instance.pause();
   }
 
   /// Switch between the front and back camera.

@@ -97,6 +97,11 @@ abstract class MobileScannerPlatform extends PlatformInterface {
     throw UnimplementedError('stop() has not been implemented.');
   }
 
+  /// Pause the camera.
+  Future<void> pause() {
+    throw UnimplementedError('pause() has not been implemented.');
+  }
+
   /// Toggle the torch on the active camera on or off.
   Future<void> toggleTorch() {
     throw UnimplementedError('toggleTorch() has not been implemented.');

@@ -128,6 +128,11 @@ abstract class BarcodeReader {
     throw UnimplementedError('start() has not been implemented.');
   }
 
+  /// Pause the barcode reader.
+  Future<void> pause() {
+    throw UnimplementedError('pause() has not been implemented.');
+  }
+
   /// Stop the barcode reader and dispose of the video stream.
   Future<void> stop() {
     throw UnimplementedError('stop() has not been implemented.');

@@ -271,6 +271,11 @@ class MobileScannerWeb extends MobileScannerPlatform {
       );
     }
 
+    // If the previous state is a pause, reset scanner.
+    if (_barcodesSubscription != null && _barcodesSubscription!.isPaused) {
+      await stop();
+    }
+
     _barcodeReader = ZXingBarcodeReader();
 
     await _barcodeReader?.maybeLoadLibrary(
@@ -358,6 +363,12 @@ class MobileScannerWeb extends MobileScannerPlatform {
   }
 
   @override
+  Future<void> pause() async {
+    _barcodesSubscription?.pause();
+    await _barcodeReader?.pause();
+  }
+
+  @override
   Future<void> stop() async {
     // Ensure the barcode scanner is stopped, by cancelling the subscription.
     await _barcodesSubscription?.cancel();

@@ -169,6 +169,11 @@ final class ZXingBarcodeReader extends BarcodeReader {
   }
 
   @override
+  Future<void> pause() async {
+    _reader?.videoElement?.pause();
+  }
+
+  @override
   Future<void> stop() async {
     _onMediaTrackSettingsChanged = null;
     _reader?.stopContinuousDecode.callAsFunction(_reader);

@@ -38,6 +38,14 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin, FlutterStreamHandler,
 
     var position = AVCaptureDevice.Position.back
     
+    private var stopped: Bool {
+        return device == nil || captureSession == nil
+    }
+
+    private var paused: Bool {
+        return stopped && textureId != nil
+    }
+
     public static func register(with registrar: FlutterPluginRegistrar) {
         let instance = MobileScannerPlugin(registrar.textures)
         let method = FlutterMethodChannel(name:
@@ -67,6 +75,8 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin, FlutterStreamHandler,
             setScale(call, result)
         case "resetScale":
             resetScale(call, result)
+        case "pause":
+            pause(result)
         case "stop":
             stop(result)
         case "updateScanWindow":
@@ -276,7 +286,7 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin, FlutterStreamHandler,
             return
         }
 
-        textureId = registry.register(self)
+        textureId = textureId ?? registry.register(self)
         captureSession = AVCaptureSession()
 
         let argReader = MapArgumentReader(call.arguments as? [String: Any])
@@ -438,28 +448,49 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin, FlutterStreamHandler,
         result(nil)
     }
 
+    func pause(_ result: FlutterResult) {
+        if (paused || stopped) {
+            result(nil)
+
+            return
+        }
+        releaseCamera()
+    }
+
     func stop(_ result: FlutterResult) {
-        if (device == nil || captureSession == nil) {
+        if (!paused && stopped) {
             result(nil)
 
             return
         }
-        captureSession!.stopRunning()
-        for input in captureSession!.inputs {
-            captureSession!.removeInput(input)
+        releaseCamera()
+        releaseTexture()
+
+        result(nil)
     }
-        for output in captureSession!.outputs {
-            captureSession!.removeOutput(output)
+
+    private func releaseCamera() {
+        guard let captureSession = captureSession else {
+            return
+        }
+
+        captureSession.stopRunning()
+        for input in captureSession.inputs {
+            captureSession.removeInput(input)
+        }
+        for output in captureSession.outputs {
+            captureSession.removeOutput(output)
         }
         device.removeObserver(self, forKeyPath: #keyPath(AVCaptureDevice.torchMode))
-        registry.unregisterTexture(textureId)
 
         latestBuffer = nil
-        captureSession = nil
+        self.captureSession = nil
         device = nil
-        textureId = nil
+    }
 
-        result(nil)
+    private func releaseTexture() {
+        registry.unregisterTexture(textureId)
+        textureId = nil
     }
 
     func analyzeImage(_ call: FlutterMethodCall, _ result: @escaping FlutterResult) {