Fix black screen issue when taking photos on Huawei phones

[lancexin]

After taking a photo on some Huawei phones and entering again, the preview screen will turn black.

The reason is that the exposure was not reset before returning the image

[AlexV525]

Would it be better to call these methods after the preview is paused?

[lancexin]

I have tried it before, but I found that there are some issues with doing so. Here is the code I have modified:

   await controller.pausePreview();
    //The photo has been taken and we need to reset the focus and exposure here
    await wrapControllerMethod<void>('setFocusMode', () async {
      realDebugPrint("wrapControllerMethod  setFocusMode start");
      await innerController?.setFocusMode(FocusMode.auto);
      realDebugPrint("wrapControllerMethod  setFocusMode end");
    }).catchError((e, s) {
      realDebugPrint("wrapControllerMethod setFocusMode error $e");
      return Future.value();
    });
    if (previousExposureMode != ExposureMode.locked) {
      await wrapControllerMethod<void>('setExposureMode', () async {
        realDebugPrint("wrapControllerMethod  setExposureMode start");
        await innerController?.setExposureMode(previousExposureMode);
        //never called here
        realDebugPrint("wrapControllerMethod  setExposureMode end");
      }).catchError((e, s) {
        realDebugPrint("wrapControllerMethod setExposureMode error $e");
        return Future.value();
      });
    }

[CameraPicker - LOG] 0:00:00.156427 for controller's initialization.
[CameraPicker - LOG] 0:00:00.092799 for config's update.
[CameraPicker - LOG] wrapControllerMethod  setFocusMode start
[CameraPicker - LOG] wrapControllerMethod  setFocusMode end
[CameraPicker - LOG] wrapControllerMethod  setExposureMode start
//block here and never print 'wrapControllerMethod  setExposureMode end'

I found that calling pausePreview and then calling the setExposureMode method would block, and I haven't figured out why this is happening yet. I found that someone in the Issues also mentioned that calling setExposureMode/setFocusMode during initialization can also be blocked. I guess there is some bug among Huawei phones.

But I found that by changing the code to the following (changing the position of pausePreview), the blocking disappeared:

      //The photo has been taken and we need to reset the focus and exposure here
      await wrapControllerMethod<void>('setFocusMode', () async {
        realDebugPrint("wrapControllerMethod  setFocusMode start");
        await innerController?.setFocusMode(FocusMode.auto);
        realDebugPrint("wrapControllerMethod  setFocusMode end");
      }).catchError((e, s) {
        realDebugPrint("wrapControllerMethod setFocusMode error $e");
        return Future.value();
      });
      if (previousExposureMode != ExposureMode.locked) {
        await wrapControllerMethod<void>('setExposureMode', () async {
          realDebugPrint("wrapControllerMethod  setExposureMode start");
          await innerController?.setExposureMode(previousExposureMode);
          //never called here
          realDebugPrint("wrapControllerMethod  setExposureMode end");
        }).catchError((e, s) {
          realDebugPrint("wrapControllerMethod setExposureMode error $e");
          return Future.value();
        });
      }
      await controller.pausePreview();

[CameraPicker - LOG] 0:00:00.225070 for controller's initialization.
[CameraPicker - LOG] 0:00:00.038097 for config's update.
[CameraPicker - LOG] wrapControllerMethod  setFocusMode start
[CameraPicker - LOG] wrapControllerMethod  setFocusMode end
[CameraPicker - LOG] wrapControllerMethod  setExposureMode start
[CameraPicker - LOG] wrapControllerMethod  setExposureMode end
[CameraPicker - LOG] Preview image cache evicted: true