在屏幕旋转后调用Camera.Release()后，正在使用摄像头 [英] Camera is being used after Camera.release() was called after screen rotation

问题描述

我有一款可以在计时器上拍照的应用程序。通常情况下，它工作得很好，除了在相机休眠时旋转屏幕的情况。谁能告诉我为什么它在睡眠状态下旋转后无法拍照？

正常情况下，当摄像机进入睡眠状态并被唤醒时，它会执行...

@Override
protected void onPause() {
    super.onPause();
    camera.stopPreview();
    camera.release();
    //camera = null;  //this give me a null object message
}

@Override
protected void onResume() {
    super.onResume();
    camera = Camera.open(cameraId);
    setCameraDisplayOrientation();
    startCameraPreview(surfaceHolder, surfaceView.getWidth(), surfaceView.getHeight());
}

但是，当摄像头在休眠状态下旋转后被唤醒时，它首先执行onResume()、Surface eChanged()、onPause()、onStop(空)、onDestroy(空)，然后执行以下命令：

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    surfaceView = (SurfaceView) findViewById(R.id.surface);
    surfaceHolder = surfaceView.getHolder();
    surfaceHolder.addCallback(this);  
} 

@Override
protected void onStart() {
    super.onStart();
}

@Override
protected void onResume() {
    super.onResume();
    camera = Camera.open(cameraId);
    setCameraDisplayOrientation();
    startCameraPreview(surfaceHolder, surfaceView.getWidth(), surfaceView.getHeight());
}

@Override
public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
    camera.stopPreview();
    setCameraDisplayOrientation();
    startCameraPreview(holder, w, h);
}

public void setCameraDisplayOrientation() {
    deviceRotation = getWindowManager().getDefaultDisplay().getRotation();
    int degrees = 0;
    switch(deviceRotation) {
        case Surface.ROTATION_0: degrees=0; break;//vertical
        case Surface.ROTATION_90: degrees=-90; break; //left side
        case Surface.ROTATION_180: degrees=180; break; //upside-down
        case Surface.ROTATION_270: degrees=90; break; //right side
    }
    Camera.CameraInfo info = new Camera.CameraInfo();
    Camera.getCameraInfo(cameraId, info);
    displayRotation = info.orientation + degrees;
    camera.setDisplayOrientation(displayRotation); //changes orientation of camera's display
}

public void startCameraPreview(SurfaceHolder holder, int w, int h) {
    double targetRatio = 0;
    switch(deviceRotation) {
        case Surface.ROTATION_0: targetRatio = (double)w/(double)h; break; //vertical
        case Surface.ROTATION_90: targetRatio = (double)h/(double)w; break; //left side
        case Surface.ROTATION_180: targetRatio = (double)w/(double)h; break; //upside-down
        case Surface.ROTATION_270: targetRatio = (double)h/(double)w; break; //right side
    }
    Camera.Parameters p = camera.getParameters();
    List<Camera.Size> previewSizes = p.getSupportedPreviewSizes();
    int optimal_h = 2; //always refers to short length in PreviewSizes
    int optimal_w = 1; //always refers to long length in PreviewSizes
    for(Camera.Size previewSize : previewSizes) {
        if (Math.abs((double)previewSize.height/(double)previewSize.width - targetRatio) <
                Math.abs((double)optimal_h/(double)optimal_w - targetRatio)) {
            optimal_h = previewSize.height;
            optimal_w = previewSize.width;
        }
    }
    p.setPreviewSize(optimal_w, optimal_h); //defines ratio of image preview - sizes can be larger than actual display
    p.set("rotation", displayRotation); //required to orient final jpeg file correctly
    camera.setParameters(p);
    ViewGroup.LayoutParams surfaceParams = surfaceView.getLayoutParams();
    switch(deviceRotation) { //aligns ratio of surface view to ratio of image preview
        case Surface.ROTATION_0:
            surfaceParams.width=ViewGroup.LayoutParams.MATCH_PARENT;
            surfaceParams.height=(int)(w*(double)optimal_w/(double)optimal_h);
            break; //vertical
        case Surface.ROTATION_90:
            surfaceParams.width=(int)(h*(double)optimal_w/(double)optimal_h);
            surfaceParams.height=ViewGroup.LayoutParams.MATCH_PARENT;
            break; //left side
        case Surface.ROTATION_180:
            surfaceParams.width=ViewGroup.LayoutParams.MATCH_PARENT;
            surfaceParams.height=(int)(w*(double)optimal_w/(double)optimal_h);
            break; //upside-down
        case Surface.ROTATION_270:
            surfaceParams.width=(int)(h*(double)optimal_w/(double)optimal_h);
            surfaceParams.height=ViewGroup.LayoutParams.MATCH_PARENT;
            break; //right side
    }
    surfaceView.setLayoutParams(surfaceParams);
    camera.setPreviewDisplay(holder); //required to startPreview
    camera.startPreview();
}

这不是完整的代码。这段代码确实会产生一些次要的图像格式错误，但它仍然说明了这个问题。为了简单起见，我去掉了一些东西。主要问题是，当它试图在休眠状态下旋转后拍摄一张照片时，它会返回一个错误"Camera is be Used After Camera.Release()Is Call Call Camera.Release()is Used After Camera.Release()"。为什么会这样？

推荐答案

这真的是早该来了，但由于我一分钟前设法解决了我的一个类似问题，我想我应该为您和其他可能正在拼命搜索Stack的人贡献自己的力量。

因此，当您旋转设备时，您调用的是onPause和onDestroy，在那里您正在释放相机。我注意到您的onResume中确实有camera.open()，没有查看与曲面相关的代码，我无法进行评论。以下是对我有效的方法。

首先，CameraPview

`

public void surfaceChanged(SurfaceHolder surfaceHolder, int format, int width, int height) {
    try {
        this.mCamera.setPreviewDisplay(surfaceHolder);
        this.mCamera.startPreview();
    } catch (Exception e) {
    }
}


public void surfaceCreated(SurfaceHolder surfaceHolder) {
    try {
        //TODO we need this here too because on SurfaceCreated we always need to open the camera, in case its released

        this.mCamera.setPreviewDisplay(surfaceHolder);
        this.mCamera.setDisplayOrientation(90);
        //this.mCamera.startPreview();
    } catch (IOException e) {
    }
}

接下来，CameraActivity的生命周期代码

 @Override
public void onResume() {
    super.onResume();
   try{
       mCamera = openFrontFacingCameraGingerbread();
      // Add to Framelayout
       this.mCameraPreview = new CameraPreview(this, this.mCamera);
        mImage.removeAllViews();
       this.mImage.addView(this.mCameraPreview);

   }catch (RuntimeException ex){

    }



}


@Override
public void onPause() {
    super.onPause();
    captureButton.setText("Begin Capture");
    if(CameraActivity.this.timer !=null) {
        CameraActivity.this.timer.cancel();
        CameraActivity.this.timer.purge();
        CameraActivity.this.timer = null;
    }
    if (mCamera != null) {
        mCamera.setPreviewCallback(null);
        mCameraPreview.getHolder().removeCallback(mCameraPreview);
        mCamera.release();
        mCamera = null;
    }


}


@Override
protected void onDestroy(){
    super.onDestroy();
    releaseCameraAndPreview();
}

private void releaseCameraAndPreview() {

    if (mCamera != null) {
        mCamera.stopPreview();
        mCamera.release();
        mCamera = null;
    }
    if(mCameraPreview != null){
        mCameraPreview.destroyDrawingCache();
        mCameraPreview.mCamera = null;
    }
}

这篇关于在屏幕旋转后调用Camera.Release()后，正在使用摄像头的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！