PoseTrackingGraph::Stop() tries to call methods on null objects

Plugin Version or Commit ID

v0.9.1

Unity Version

2020.3.32f1

Your Host OS

Ubuntu 20.04

Target Platform

Android

Target Device

No response

[Windows Only] Visual Studio C++ and Windows SDK Version

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[Linux Only] GCC/G++ and GLIBC Version

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[Android Only] Android Build Tools and NDK Version

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[iOS Only] XCode Version

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Build Command

python build.py build --desktop gpu --android arm64 --opencv cmake

Bug Description

When PoseTrackingGraph runs in Async mode, output stream object are not initialized and remain as null. However PoseTrackingGraph Stop() method always tries to call RemoveAllListeners() method on them, and thus NullReferenceException is raised.

public override void Stop()
{
      _poseDetectionStream.RemoveAllListeners();
      _poseDetectionStream = null;
      _poseLandmarksStream.RemoveAllListeners();
      _poseLandmarksStream = null;
      _poseWorldLandmarksStream.RemoveAllListeners();
      _poseWorldLandmarksStream = null;
      _segmentationMaskStream.RemoveAllListeners();
      _segmentationMaskStream = null;
      _roiFromLandmarksStream.RemoveAllListeners();
      _roiFromLandmarksStream = null;
      base.Stop();
 }

Steps to Reproduce the Bug

Please see Bug Description.

Log

NullReferenceException: Object reference not set to an instance of an object Mediapipe.Unity.PoseTracking.PoseTrackingGraph.Stop () (at Assets/Scripts/PoseTrackingGraph.cs:117) Mediapipe.Unity.GraphRunner.OnDestroy () (at Assets/MediaPipeUnity/Samples/Common/Scripts/GraphRunner.cs:104)

Screenshot/Video

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Additional Context

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[MoneyWonders]

This issue happens because GraphRunner will call Stop() in it’s OnDestroy(), and ImageSourceSolution do the same thing in Stop(). If you like to stop MediaPipe before close app, you will meet this issue. I think the better way to avoid this problem is add null-check in GraphRunner.Stop(), just like: public override void Stop() { _palmDetectionsStream?.RemoveAllListeners(); _palmDetectionsStream = null; _handRectsFromPalmDetectionsStream?.RemoveAllListeners(); _handRectsFromPalmDetectionsStream = null; _handLandmarksStream?.RemoveAllListeners(); _handLandmarksStream = null; _handWorldLandmarksStream?.RemoveAllListeners(); _handWorldLandmarksStream = null; _handRectsFromLandmarksStream?.RemoveAllListeners(); _handRectsFromLandmarksStream = null; _handednessStream?.RemoveAllListeners(); _handednessStream = null; base.Stop(); }

[wonwoolee]

I agree with the solution @MoneyWonders proposed, which is simple and elegant 😄 I applied it to my code and it addressed my issue.