feat: add pause feature

android/src/main/kotlin/dev/steenbakker/mobile_scanner/MobileScanner.kt

@@ -274,7 +274,7 @@ class MobileScanner(
             }
 
             cameraProvider?.unbindAll()
-            textureEntry = textureRegistry.createSurfaceTexture()
+            textureEntry = textureEntry ?: textureRegistry.createSurfaceTexture()
 
             // Preview
             val surfaceProvider = Preview.SurfaceProvider { request ->
@@ -406,14 +406,33 @@ 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
 
@@ -431,9 +450,6 @@ 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()
@@ -445,7 +461,13 @@ 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.

android/src/main/kotlin/dev/steenbakker/mobile_scanner/MobileScannerExceptions.kt

@@ -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()

android/src/main/kotlin/dev/steenbakker/mobile_scanner/MobileScannerHandler.kt

@@ -123,6 +123,7 @@ class MobileScannerHandler(
                     }
                 })
             "start" -> start(call, result)
+            "pause" -> pause(result)
             "stop" -> stop(result)
             "toggleTorch" -> toggleTorch(result)
             "analyzeImage" -> analyzeImage(call, result)
@@ -230,6 +231,18 @@ 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()

example/lib/barcode_scanner_controller.dart

@@ -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),

example/lib/scanner_button_widgets.dart

@@ -175,3 +175,30 @@ 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();
+          },
+        );
+      },
+    );
+  }
+}

ios/Classes/MobileScanner.swift

@@ -60,6 +60,14 @@ public class MobileScanner: NSObject, AVCaptureVideoDataOutputSampleBufferDelega
     private var imagesCurrentlyBeingProcessed = false
 
     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
@@ -126,6 +134,7 @@ 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 {
             print("Failed to get image buffer from sample buffer.")
             return
@@ -180,7 +189,7 @@ 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)
@@ -294,28 +303,50 @@ public class MobileScanner: NSObject, AVCaptureVideoDataOutputSampleBufferDelega
             completion(MobileScannerStartParameters())
         }
     }
+
+    /// 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
     }
 
     /// Toggle the torch.

ios/Classes/MobileScannerError.swift

@@ -10,6 +10,7 @@ enum MobileScannerError: Error {
     case noCamera
     case alreadyStarted
     case alreadyStopped
+    case alreadyPaused
     case cameraError(_ error: Error)
     case zoomWhenStopped
     case zoomError(_ error: Error)

ios/Classes/MobileScannerPlugin.swift

@@ -78,6 +78,8 @@ 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":
@@ -147,6 +149,14 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin {
                                 details: nil))
         }
     }
+
+    /// 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) {

lib/src/method_channel/mobile_scanner_method_channel.dart

@@ -38,6 +38,7 @@ class MethodChannelMobileScanner extends MobileScannerPlatform {
   }
 
   int? _textureId;
+  bool _pausing = false;
 
   /// Parse a [BarcodeCapture] from the given [event].
   BarcodeCapture? _parseBarcode(Map<Object?, Object?>? event) {
@@ -184,7 +185,7 @@ 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(
@@ -254,6 +255,8 @@ class MethodChannelMobileScanner extends MobileScannerPlatform {
       size = Size(width, height);
     }
 
+    _pausing = false;
+
     return MobileScannerViewAttributes(
       currentTorchMode: currentTorchState,
       numberOfCameras: numberOfCameras,
@@ -268,10 +271,22 @@ 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');

lib/src/mobile_scanner_controller.dart

@@ -170,6 +170,30 @@ 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.
@@ -317,31 +341,21 @@ 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;
-    }
-
-    _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,
-    );
-
+    _stop();
     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.
   ///
   /// Does nothing if the device has less than 2 cameras.