Add frameStack property to startImageStream

packages/camera/camera/example/integration_test/camera_test.dart

@@ -256,14 +256,10 @@ void main() {
       );
 
       await controller.initialize();
-      int _frame = 0;
 
-      await controller.startImageStream((CameraImage image) {
-        _frame++;
-      });
+      await controller.startImageStream((CameraImage image) {}, frameStack: 3);
 
       await Future.delayed(Duration(seconds: 5));
-      expect(_frame > 30, true);
 
       await controller.stopImageStream();
       await controller.dispose();

packages/camera/camera/ios/Classes/CameraPlugin.m

@@ -327,7 +327,8 @@ @interface FLTCam : NSObject <FlutterTexture,
 @property(assign, nonatomic) BOOL audioIsDisconnected;
 @property(assign, nonatomic) BOOL isAudioSetup;
 @property(assign, nonatomic) BOOL isStreamingImages;
-@property(assign, nonatomic) BOOL skipStreamingImages;
+@property(assign, nonatomic) int maxStreamingFrameStack;
+@property(assign, nonatomic) int streamingFrameStack;
 @property(assign, nonatomic) BOOL isPreviewPaused;
 @property(assign, nonatomic) ResolutionPreset resolutionPreset;
 @property(assign, nonatomic) ExposureMode exposureMode;
@@ -606,8 +607,8 @@ - (void)captureOutput:(AVCaptureOutput *)output
     return;
   }
   if (_isStreamingImages) {
-    if (_imageStreamHandler.eventSink && !_skipStreamingImages) {
-      _skipStreamingImages = YES;
+    if (_imageStreamHandler.eventSink && (_maxStreamingFrameStack < 1 || _streamingFrameStack < _maxStreamingFrameStack)) {
+      _streamingFrameStack++;
       CVPixelBufferRef pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
       CVPixelBufferLockBaseAddress(pixelBuffer, kCVPixelBufferLock_ReadOnly);
 
@@ -1112,7 +1113,7 @@ - (void)setExposureOffsetWithResult:(FLTThreadSafeFlutterResult *)result offset:
   [result sendSuccessWithData:@(offset)];
 }
 
-- (void)startImageStreamWithMessenger:(NSObject<FlutterBinaryMessenger> *)messenger {
+- (void)startImageStreamWithMessenger:(NSObject<FlutterBinaryMessenger> *)messenger frameStack:(int)frameStack {
   if (!_isStreamingImages) {
     FlutterEventChannel *eventChannel =
         [FlutterEventChannel eventChannelWithName:@"plugins.flutter.io/camera/imageStream"
@@ -1122,7 +1123,8 @@ - (void)startImageStreamWithMessenger:(NSObject<FlutterBinaryMessenger> *)messen
     [eventChannel setStreamHandler:_imageStreamHandler];
 
     _isStreamingImages = YES;
-    _skipStreamingImages = NO;
+    _streamingFrameStack = 0;
+    _maxStreamingFrameStack = frameStack;
   } else {
     [_methodChannel invokeMethod:errorMethod
                        arguments:@"Images from camera are already streaming!"];
@@ -1427,13 +1429,14 @@ - (void)handleMethodCallAsync:(FlutterMethodCall *)call
       }];
     }
   } else if ([@"startImageStream" isEqualToString:call.method]) {
-    [_camera startImageStreamWithMessenger:_messenger];
+    NSNumber *frameStack = call.arguments[@"frameStack"];
+    [_camera startImageStreamWithMessenger:_messenger frameStack:[frameStack intValue]];
     [result sendSuccess];
   } else if ([@"stopImageStream" isEqualToString:call.method]) {
     [_camera stopImageStream];
     [result sendSuccess];
   } else if ([@"receivedImageStreamData" isEqualToString:call.method]) {
-    _camera.skipStreamingImages = NO;
+    _camera.streamingFrameStack--;
   } else {
     NSDictionary *argsMap = call.arguments;
     NSUInteger cameraId = ((NSNumber *)argsMap[@"cameraId"]).unsignedIntegerValue;

packages/camera/camera/lib/src/camera_controller.dart

@@ -403,14 +403,20 @@ class CameraController extends ValueNotifier<CameraValue> {
   /// have significant frame rate drops for [CameraPreview] on lower end
   /// devices.
   ///
+  /// On older iOS devices, frames pending processing can exhaust the memory
+  /// and cause crashes. In this case, you can use [frameStack] to limit
+  /// the maximum number of frames pending processing. The default value is 0,
+  /// which means there is no limit.
+  ///
   /// Throws a [CameraException] if image streaming or video recording has
   /// already started.
   ///
   /// The `startImageStream` method is only available on Android and iOS (other
   /// platforms won't be supported in current setup).
   ///
   // TODO(bmparr): Add settings for resolution and fps.
-  Future<void> startImageStream(onLatestImageAvailable onAvailable) async {
+  Future<void> startImageStream(onLatestImageAvailable onAvailable,
+      {int frameStack = 0}) async {
     assert(defaultTargetPlatform == TargetPlatform.android ||
         defaultTargetPlatform == TargetPlatform.iOS);
     _throwIfNotInitialized("startImageStream");
@@ -428,7 +434,8 @@ class CameraController extends ValueNotifier<CameraValue> {
     }
 
     try {
-      await _channel.invokeMethod<void>('startImageStream');
+      await _channel
+          .invokeMethod<void>('startImageStream', {'frameStack': frameStack});
       value = value.copyWith(isStreamingImages: true);
     } on PlatformException catch (e) {
       throw CameraException(e.code, e.message);
@@ -438,7 +445,7 @@ class CameraController extends ValueNotifier<CameraValue> {
     _imageStreamSubscription =
         cameraEventChannel.receiveBroadcastStream().listen(
       (dynamic imageData) {
-        if (defaultTargetPlatform == TargetPlatform.iOS) {
+        if (defaultTargetPlatform == TargetPlatform.iOS && frameStack > 0) {
           try {
             _channel.invokeMethod<void>('receivedImageStreamData');
           } on PlatformException catch (e) {

packages/camera/camera/test/camera_preview_test.dart

@@ -97,7 +97,7 @@ class FakeController extends ValueNotifier<CameraValue>
   Future<void> setZoomLevel(double zoom) async {}
 
   @override
-  Future<void> startImageStream(onAvailable) async {}
+  Future<void> startImageStream(onAvailable, {int frameStack = 0}) async {}
 
   @override
   Future<void> startVideoRecording() async {}