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[camera] Adding check for null before creating capture session. #2965

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[camera] Adding check for null before creating capture session. #2965

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4 changes: 4 additions & 0 deletions packages/camera/CHANGELOG.md
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Original file line number Diff line number Diff line change
@@ -1,3 +1,7 @@
## 0.5.9

* Fix rare nullptr exception on Android.

## 0.5.8+6

* Avoiding uses or overrides a deprecated API in CameraPlugin.java.
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4 changes: 3 additions & 1 deletion packages/camera/android/src/main/java/io/flutter/plugins/camera/Camera.java
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Expand Up @@ -421,7 +421,9 @@ public void resumeVideoRecording(@NonNull final Result result) {
}

public void startPreview() throws CameraAccessException {
createCaptureSession(CameraDevice.TEMPLATE_PREVIEW, pictureImageReader.getSurface());
if (pictureImageReader != null) {
createCaptureSession(CameraDevice.TEMPLATE_PREVIEW, pictureImageReader.getSurface());
}
Comment on lines +424 to +426
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nit: you could invert the if statement to reduce nesting and would make it a bit easier to expand the method:

Suggested change
if (pictureImageReader != null) {
createCaptureSession(CameraDevice.TEMPLATE_PREVIEW, pictureImageReader.getSurface());
}
if (pictureImageReader == null) {
return;
}
createCaptureSession(CameraDevice.TEMPLATE_PREVIEW, pictureImageReader.getSurface());

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@mvanbeusekom mvanbeusekom Sep 22, 2020 •
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Looking further into this issue, it would be good to know why pictureImageReader is null at this point and if that is valid (as @tvolkert also mentioned in his comments on PR #2871 ).

If the pictureImageReader should not be null when startPreview is called, this code will hide a mistake that is somewhere else in the code. I will start looking into this.

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Thanks Maurits for looking into this! I agree that this is only a workaround for a symptom, but not a proper fix. Do you have a hunch where the real problem could lie?

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Hi @panmari, we (me and a colleague) have been looking into this issue and can't quite reproduce it as of yet. We do have 2 theories at the moment:

  1. Since version 0.5.0 developers are responsible for handling application lifecycle events that might affect the plugin (see also this comment mentioned by @kevin-lot). If these events are not handled correctly it might cause the issue where the permission system moves the app to the background and not reinitialize the camera plugin correctly (leaving it in an invalid state);
  2. We could did get the same error when (using the example app) very rapidly switching between the front and back facing cameras. We noticed that in these cases the onOpened callback would be called when the dispose method has already been run (race condition).

I am currently discussing on how we should approach these problems.

}

public void startPreviewWithImageStream(EventChannel imageStreamChannel)
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2 changes: 1 addition & 1 deletion packages/camera/pubspec.yaml
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Expand Up @@ -2,7 +2,7 @@ name: camera
description: A Flutter plugin for getting information about and controlling the
camera on Android and iOS. Supports previewing the camera feed, capturing images, capturing video,
and streaming image buffers to dart.
version: 0.5.8+6
version: 0.5.9

homepage: https://github.com/flutter/plugins/tree/master/packages/camera

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