Updated iOS object detector to use delegates instead of callbacks for async calls

mediapipe/tasks/ios/test/vision/object_detector/MPPObjectDetectorTests.m

@@ -25,6 +25,8 @@ static NSDictionary *const kCatsAndDogsRotatedImage =
 static NSString *const kExpectedErrorDomain = @"com.google.mediapipe.tasks";
 static const float pixelDifferenceTolerance = 10.0f;
 static const float scoreDifferenceTolerance = 0.02f;
+static NSString *const kLiveStreamTestsDictObjectDetectorKey = @"object_detector";
+static NSString *const kLiveStreamTestsDictExpectationKey = @"expectation";
 
 #define AssertEqualErrors(error, expectedError)                                               \
   XCTAssertNotNil(error);                                                                     \
@@ -58,7 +60,10 @@ static const float scoreDifferenceTolerance = 0.02f;
   XCTAssertEqualWithAccuracy(boundingBox.size.height, expectedBoundingBox.size.height, \
                              pixelDifferenceTolerance, @"index i = %d", idx);
 
-@interface MPPObjectDetectorTests : XCTestCase
+@interface MPPObjectDetectorTests : XCTestCase <MPPObjectDetectorLiveStreamDelegate> {
+  NSDictionary *liveStreamSucceedsTestDict;
+  NSDictionary *outOfOrderTimestampTestDict;
+}
 @end
 
 @implementation MPPObjectDetectorTests
@@ -446,31 +451,28 @@ static const float scoreDifferenceTolerance = 0.02f;
 
 #pragma mark Running Mode Tests
 
-- (void)testCreateObjectDetectorFailsWithResultListenerInNonLiveStreamMode {
+- (void)testCreateObjectDetectorFailsWithDelegateInNonLiveStreamMode {
   MPPRunningMode runningModesToTest[] = {MPPRunningModeImage, MPPRunningModeVideo};
   for (int i = 0; i < sizeof(runningModesToTest) / sizeof(runningModesToTest[0]); i++) {
     MPPObjectDetectorOptions *options = [self objectDetectorOptionsWithModelName:kModelName];
 
     options.runningMode = runningModesToTest[i];
-    options.completion =
+    options.objectDetectorLiveStreamDelegate = self;
-        ^(MPPObjectDetectionResult *result, NSInteger timestampInMilliseconds, NSError *error) {
-        };
 
     [self
         assertCreateObjectDetectorWithOptions:options
                        failsWithExpectedError:
-                           [NSError
+                           [NSError errorWithDomain:kExpectedErrorDomain
-                               errorWithDomain:kExpectedErrorDomain
                                                code:MPPTasksErrorCodeInvalidArgumentError
                                            userInfo:@{
                                              NSLocalizedDescriptionKey :
-                                            @"The vision task is in image or video mode, a "
+                                                 @"The vision task is in image or video mode. The "
-                                            @"user-defined result callback should not be provided."
+                                                 @"delegate must not be set in the task's options."
                                            }]];
   }
 }
 
-- (void)testCreateObjectDetectorFailsWithMissingResultListenerInLiveStreamMode {
+- (void)testCreateObjectDetectorFailsWithMissingDelegateInLiveStreamMode {
   MPPObjectDetectorOptions *options = [self objectDetectorOptionsWithModelName:kModelName];
 
   options.runningMode = MPPRunningModeLiveStream;
@@ -481,8 +483,11 @@ static const float scoreDifferenceTolerance = 0.02f;
                                                code:MPPTasksErrorCodeInvalidArgumentError
                                            userInfo:@{
                                              NSLocalizedDescriptionKey :
-                                                 @"The vision task is in live stream mode, a "
+                                                 @"The vision task is in live stream mode. An "
-                                                 @"user-defined result callback must be provided."
+                                                 @"object must be set as the "
+                                                 @"delegate of the task in its options to ensure "
+                                                 @"asynchronous delivery of "
+                                                 @"results."
                                            }]];
 }
 
@@ -563,10 +568,7 @@ static const float scoreDifferenceTolerance = 0.02f;
   MPPObjectDetectorOptions *options = [self objectDetectorOptionsWithModelName:kModelName];
 
   options.runningMode = MPPRunningModeLiveStream;
-  options.completion =
+  options.objectDetectorLiveStreamDelegate = self;
-      ^(MPPObjectDetectionResult *result, NSInteger timestampInMilliseconds, NSError *error) {
-
-      };
 
   MPPObjectDetector *objectDetector = [self objectDetectorWithOptionsSucceeds:options];
 
@@ -631,23 +633,17 @@ static const float scoreDifferenceTolerance = 0.02f;
   options.maxResults = maxResults;
 
   options.runningMode = MPPRunningModeLiveStream;
+  options.objectDetectorLiveStreamDelegate = self;
 
   XCTestExpectation *expectation = [[XCTestExpectation alloc]
       initWithDescription:@"detectWithOutOfOrderTimestampsAndLiveStream"];
   expectation.expectedFulfillmentCount = 1;
 
-  options.completion =
-      ^(MPPObjectDetectionResult *result, NSInteger timestampInMilliseconds, NSError *error) {
-        [self assertObjectDetectionResult:result
-                  isEqualToExpectedResult:
-                      [MPPObjectDetectorTests
-                          expectedDetectionResultForCatsAndDogsImageWithTimestampInMilliseconds:
-                              timestampInMilliseconds]
-                  expectedDetectionsCount:maxResults];
-        [expectation fulfill];
-      };
-
   MPPObjectDetector *objectDetector = [self objectDetectorWithOptionsSucceeds:options];
+  liveStreamSucceedsTestDict = @{
+    kLiveStreamTestsDictObjectDetectorKey : objectDetector,
+    kLiveStreamTestsDictExpectationKey : expectation
+  };
 
   MPPImage *image = [self imageWithFileInfo:kCatsAndDogsImage];
 
@@ -693,19 +689,15 @@ static const float scoreDifferenceTolerance = 0.02f;
   expectation.expectedFulfillmentCount = iterationCount + 1;
   expectation.inverted = YES;
 
-  options.completion =
+  options.objectDetectorLiveStreamDelegate = self;
-      ^(MPPObjectDetectionResult *result, NSInteger timestampInMilliseconds, NSError *error) {
-        [self assertObjectDetectionResult:result
-                  isEqualToExpectedResult:
-                      [MPPObjectDetectorTests
-                          expectedDetectionResultForCatsAndDogsImageWithTimestampInMilliseconds:
-                              timestampInMilliseconds]
-                  expectedDetectionsCount:maxResults];
-        [expectation fulfill];
-      };
 
   MPPObjectDetector *objectDetector = [self objectDetectorWithOptionsSucceeds:options];
 
+  liveStreamSucceedsTestDict = @{
+    kLiveStreamTestsDictObjectDetectorKey : objectDetector,
+    kLiveStreamTestsDictExpectationKey : expectation
+  };
+
   // TODO: Mimic initialization from CMSampleBuffer as live stream mode is most likely to be used
   // with the iOS camera. AVCaptureVideoDataOutput sample buffer delegates provide frames of type
   // `CMSampleBuffer`.
@@ -718,4 +710,24 @@ static const float scoreDifferenceTolerance = 0.02f;
   [self waitForExpectations:@[ expectation ] timeout:0.5];
 }
 
+#pragma mark MPPObjectDetectorLiveStreamDelegate Methods
+- (void)objectDetector:(MPPObjectDetector *)objectDetector
+    didFinishDetectionWithResult:(MPPObjectDetectionResult *)objectDetectionResult
+         timestampInMilliseconds:(NSInteger)timestampInMilliseconds
+                           error:(NSError *)error {
+  NSInteger maxResults = 4;
+  [self assertObjectDetectionResult:objectDetectionResult
+            isEqualToExpectedResult:
+                [MPPObjectDetectorTests
+                    expectedDetectionResultForCatsAndDogsImageWithTimestampInMilliseconds:
+                        timestampInMilliseconds]
+            expectedDetectionsCount:maxResults];
+
+  if (objectDetector == outOfOrderTimestampTestDict[kLiveStreamTestsDictObjectDetectorKey]) {
+    [outOfOrderTimestampTestDict[kLiveStreamTestsDictExpectationKey] fulfill];
+  } else if (objectDetector == liveStreamSucceedsTestDict[kLiveStreamTestsDictObjectDetectorKey]) {
+    [liveStreamSucceedsTestDict[kLiveStreamTestsDictExpectationKey] fulfill];
+  }
+}
+
 @end

mediapipe/tasks/ios/vision/object_detector/sources/MPPObjectDetector.h

@@ -137,6 +137,9 @@ NS_SWIFT_NAME(ObjectDetector)
  * the provided `MPPImage`. Only use this method when the `MPPObjectDetector` is created with
  * `MPPRunningModeLiveStream`. Results are provided asynchronously via the `completion` callback
  * provided in the `MPPObjectDetectorOptions`.
+ * The object which needs to be continuously notified of the available results of object
+ * detection must confirm to `MPPObjectDetectorLiveStreamDelegate` protocol and implement the
+ * `objectDetector:didFinishDetectionWithResult:timestampInMilliseconds:error:` delegate method.
  *
  * It's required to provide a timestamp (in milliseconds) to indicate when the input image is sent
  * to the object detector. The input timestamps must be monotonically increasing.

mediapipe/tasks/ios/vision/object_detector/sources/MPPObjectDetector.mm

@@ -37,8 +37,8 @@ static NSString *const kImageOutStreamName = @"image_out";
 static NSString *const kImageTag = @"IMAGE";
 static NSString *const kNormRectStreamName = @"norm_rect_in";
 static NSString *const kNormRectTag = @"NORM_RECT";
-
 static NSString *const kTaskGraphName = @"mediapipe.tasks.vision.ObjectDetectorGraph";
+static NSString *const kTaskName = @"objectDetector";
 
 #define InputPacketMap(imagePacket, normalizedRectPacket) \
   {                                                       \
@@ -51,6 +51,7 @@ static NSString *const kTaskGraphName = @"mediapipe.tasks.vision.ObjectDetectorG
   /** iOS Vision Task Runner */
   MPPVisionTaskRunner *_visionTaskRunner;
 }
+@property(nonatomic, weak) id<MPPObjectDetectorLiveStreamDelegate> objectDetectorLiveStreamDelegate;
 @end
 
 @implementation MPPObjectDetector
@@ -78,11 +79,32 @@ static NSString *const kTaskGraphName = @"mediapipe.tasks.vision.ObjectDetectorG
 
     PacketsCallback packetsCallback = nullptr;
 
-    if (options.completion) {
+    if (options.objectDetectorLiveStreamDelegate) {
+      _objectDetectorLiveStreamDelegate = options.objectDetectorLiveStreamDelegate;
+
+      // Capturing `self` as weak in order to avoid `self` being kept in memory
+      // and cause a retain cycle, after self is set to `nil`.
+      MPPObjectDetector *__weak weakSelf = self;
+      dispatch_queue_t callbackQueue =
+          dispatch_queue_create([MPPVisionTaskRunner uniqueDispatchQueueNameWithSuffix:kTaskName], NULL);
       packetsCallback = [=](absl::StatusOr<PacketMap> statusOrPackets) {
+        if (!weakSelf) {
+          return;
+        }
+        if (![weakSelf.objectDetectorLiveStreamDelegate
+                respondsToSelector:@selector
+                (objectDetector:didFinishDetectionWithResult:timestampInMilliseconds:error:)]) {
+          return;
+        }
+
         NSError *callbackError = nil;
         if (![MPPCommonUtils checkCppError:statusOrPackets.status() toError:&callbackError]) {
-          options.completion(nil, Timestamp::Unset().Value(), callbackError);
+          dispatch_async(callbackQueue, ^{
+            [weakSelf.objectDetectorLiveStreamDelegate objectDetector:weakSelf
+                                         didFinishDetectionWithResult:nil
+                                              timestampInMilliseconds:Timestamp::Unset().Value()
+                                                                error:callbackError];
+          });
           return;
         }
 
@@ -95,10 +117,15 @@ static NSString *const kTaskGraphName = @"mediapipe.tasks.vision.ObjectDetectorG
             objectDetectionResultWithDetectionsPacket:statusOrPackets.value()[kDetectionsStreamName
                                                                                   .cppString]];
 
-        options.completion(result,
+        NSInteger timeStampInMilliseconds =
             outputPacketMap[kImageOutStreamName.cppString].Timestamp().Value() /
-                               kMicroSecondsPerMilliSecond,
+            kMicroSecondsPerMilliSecond;
-                           callbackError);
+        dispatch_async(callbackQueue, ^{
+          [weakSelf.objectDetectorLiveStreamDelegate objectDetector:weakSelf
+                                       didFinishDetectionWithResult:result
+                                            timestampInMilliseconds:timeStampInMilliseconds
+                                                              error:callbackError];
+        });
       };
     }
 
@@ -112,6 +139,7 @@ static NSString *const kTaskGraphName = @"mediapipe.tasks.vision.ObjectDetectorG
       return nil;
     }
   }
+
   return self;
 }
 
@@ -224,5 +252,4 @@ static NSString *const kTaskGraphName = @"mediapipe.tasks.vision.ObjectDetectorG
   return [_visionTaskRunner processLiveStreamPacketMap:inputPacketMap.value() error:error];
 }
 
-
 @end

mediapipe/tasks/ios/vision/object_detector/sources/MPPObjectDetectorOptions.h

@@ -20,19 +20,70 @@
 
 NS_ASSUME_NONNULL_BEGIN
 
+@class MPPObjectDetector;
+
+/**
+ * This protocol defines an interface for the delegates of `MPPObjectDetector` object to receive
+ * results of performing asynchronous object detection on images
+ * (i.e, when `runningMode` = `MPPRunningModeLiveStream`).
+ *
+ * The delegate of `MPPObjectDetector` must adopt `MPPObjectDetectorLiveStreamDelegate` protocol.
+ * The methods in this protocol are optional.
+ */
+NS_SWIFT_NAME(ObjectDetectorLiveStreamDelegate)
+@protocol MPPObjectDetectorLiveStreamDelegate <NSObject>
+
+@optional
+
+/**
+ * This method notifies a delegate that the results of asynchronous object detection of
+ * an image submitted to the `MPPObjectDetector` is available.
+ *
+ * This method is called on a private serial dispatch queue created by the `MPPObjectDetector`
+ * for performing the asynchronous delegates calls.
+ *
+ * @param objectDetector The object detector which performed the object detection.
+ * This is useful to test equality when there are multiple instances of `MPPObjectDetector`.
+ * @param result The `MPPObjectDetectionResult` object that contains a list of detections, each
+ * detection has a bounding box that is expressed in the unrotated input frame of reference
+ * coordinates system, i.e. in `[0,image_width) x [0,image_height)`, which are the dimensions of the
+ * underlying image data.
+ * @param timestampInMilliseconds The timestamp (in milliseconds) which indicates when the input
+ * image was sent to the object detector.
+ * @param error An optional error parameter populated when there is an error in performing object
+ * detection on the input live stream image data.
+ *
+ */
+- (void)objectDetector:(MPPObjectDetector *)objectDetector
+    didFinishDetectionWithResult:(nullable MPPObjectDetectionResult *)result
+         timestampInMilliseconds:(NSInteger)timestampInMilliseconds
+                           error:(nullable NSError *)error
+    NS_SWIFT_NAME(objectDetector(_:didFinishDetection:timestampInMilliseconds:error:));
+@end
+
 /** Options for setting up a `MPPObjectDetector`. */
 NS_SWIFT_NAME(ObjectDetectorOptions)
 @interface MPPObjectDetectorOptions : MPPTaskOptions <NSCopying>
 
+/**
+ * Running mode of the object detector task. Defaults to `MPPRunningModeImage`.
+ * `MPPImageClassifier` can be created with one of the following running modes:
+ *  1. `MPPRunningModeImage`: The mode for performing object detection on single image inputs.
+ *  2. `MPPRunningModeVideo`: The mode for performing object detection on the decoded frames of a
+ *      video.
+ *  3. `MPPRunningModeLiveStream`: The mode for performing object detection on a live stream of
+ *      input data, such as from the camera.
+ */
 @property(nonatomic) MPPRunningMode runningMode;
 
 /**
- * The user-defined result callback for processing live stream data. The result callback should only
+ * An object that confirms to `MPPObjectDetectorLiveStreamDelegate` protocol. This object must
- * be specified when the running mode is set to the live stream mode.
+ * implement `objectDetector:didFinishDetectionWithResult:timestampInMilliseconds:error:` to receive
- * TODO: Add parameter `MPPImage` in the callback.
+ * the results of performing asynchronous object detection on images (i.e, when `runningMode` =
+ * `MPPRunningModeLiveStream`).
  */
-@property(nonatomic, copy) void (^completion)
+@property(nonatomic, weak, nullable) id<MPPObjectDetectorLiveStreamDelegate>
-    (MPPObjectDetectionResult *__nullable result, NSInteger timestampMs, NSError *error);
+    objectDetectorLiveStreamDelegate;
 
 /**
  * The locale to use for display names specified through the TFLite Model Metadata, if any. Defaults

mediapipe/tasks/ios/vision/object_detector/sources/MPPObjectDetectorOptions.m

@@ -33,7 +33,7 @@
   objectDetectorOptions.categoryDenylist = self.categoryDenylist;
   objectDetectorOptions.categoryAllowlist = self.categoryAllowlist;
   objectDetectorOptions.displayNamesLocale = self.displayNamesLocale;
-  objectDetectorOptions.completion = self.completion;
+  objectDetectorOptions.objectDetectorLiveStreamDelegate = self.objectDetectorLiveStreamDelegate;
 
   return objectDetectorOptions;
 }