在开发相机应用程序的过程中，我遇到了一个例外情况，只有当我切换到其他应用程序（我的应用为onPause()）时才会发生这种情况。
01-15 17:22:15.017: E/AndroidRuntime(14336): FATAL EXCEPTION: main
01-15 17:22:15.017: E/AndroidRuntime(14336): java.lang.RuntimeException: Method called after release()
01-15 17:22:15.017: E/AndroidRuntime(14336): at android.hardware.Camera.setPreviewDisplay(Native Method)
01-15 17:22:15.017: E/AndroidRuntime(14336): at android.hardware.Camera.setPreviewDisplay(Camera.java:357)
01-15 17:22:15.017: E/AndroidRuntime(14336): at com.sora.cbir.yuki.image.leaf.CameraPreview.surfaceCreated(CameraPreview.java:32)
01-15 17:22:15.017: E/AndroidRuntime(14336): at android.view.SurfaceView.updateWindow(SurfaceView.java:551)
01-15 17:22:15.017: E/AndroidRuntime(14336): at android.view.SurfaceView.onWindowVisibilityChanged(SurfaceView.java:213)
01-15 17:22:15.017: E/AndroidRuntime(14336): at android.view.View.dispatchWindowVisibilityChanged(View.java:4075)
01-15 17:22:15.017: E/AndroidRuntime(14336): at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:742)
01-15 17:22:15.017: E/AndroidRuntime(14336): at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:742)
01-15 17:22:15.017: E/AndroidRuntime(14336): at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:742)
01-15 17:22:15.017: E/AndroidRuntime(14336): at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:742)
01-15 17:22:15.017: E/AndroidRuntime(14336): at android.view.ViewRoot.performTraversals(ViewRoot.java:858)
01-15 17:22:15.017: E/AndroidRuntime(14336): at android.view.ViewRoot.handleMessage(ViewRoot.java:1995)
01-15 17:22:15.017: E/AndroidRuntime(14336): at android.os.Handler.dispatchMessage(Handler.java:99)
01-15 17:22:15.017: E/AndroidRuntime(14336): at android.os.Looper.loop(Looper.java:150)
01-15 17:22:15.017: E/AndroidRuntime(14336): at android.app.ActivityThread.main(ActivityThread.java:4389)
01-15 17:22:15.017: E/AndroidRuntime(14336): at java.lang.reflect.Method.invokeNative(Native Method)
01-15 17:22:15.017: E/AndroidRuntime(14336): at java.lang.reflect.Method.invoke(Method.java:507)
01-15 17:22:15.017: E/AndroidRuntime(14336): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:849)
01-15 17:22:15.017: E/AndroidRuntime(14336): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:607)
01-15 17:22:15.017: E/AndroidRuntime(14336): at dalvik.system.NativeStart.main(Native Method)
我做了一些研究，发现我需要添加
mCamera.setPreviewCallback(null);
作为Android相机堆栈的解决方法
我的onPause()现在看起来像这样：
@Override
protected void onPause() {
super.onPause();
try
{
// release the camera immediately on pause event
//releaseCamera();
mCamera.stopPreview();
mCamera.setPreviewCallback(null);
mCamera.release();
mCamera = null;
}
catch(Exception e)
{
e.printStackTrace();
}
}
和我的onResume()：
@Override
protected void onResume()
{
super.onResume();
try
{
mCamera.setPreviewCallback(null);
mCamera = getCameraInstance();
//mCamera.setPreviewCallback(null);
mPreview = new CameraPreview(Imageupload.this, mCamera);//set preview
preview.addView(mPreview);
} catch (Exception e){
Log.d(TAG, "Error starting camera preview: " + e.getMessage());
}
}
}
最后是我的getCameraInstance()方法：
public Camera getCameraInstance(){
Camera camera = null;
try {
camera = Camera.open(); // attempt to get a Camera instance
}
catch (Exception e){
// Camera is not available (in use or does not exist)
}
Camera.Parameters parameters = camera.getParameters();
//mPreviewSize = getBestPreviewSize(parameters, wt, ht);
//mPictureSize = getBestPictureSize(parameters, wt, ht);
//Shift W & H => if camera rotates 90 deg
mPreviewSize = getOptimalPreviewSize(parameters, wt, ht); //original => wt,ht
mPictureSize = getOptimalPictureSize(parameters, wt, ht); //original => wt,ht
Log.d("CAMERA", "SCREEN RESOLUTION H: "+ht);
Log.d("CAMERA", "SCREEN RESOLUTION W: "+wt);
Log.d("CAMERA", "PREVIEW RESOLUTION H: "+mPreviewSize.height);
Log.d("CAMERA", "PREVIEW RESOLUTION W: "+mPreviewSize.width);
Log.d("CAMERA", "PICTURE RESOLUTION H: "+mPictureSize.height);
Log.d("CAMERA", "PICTURE RESOLUTION W: "+mPictureSize.width);
//set preview size based on device screen
parameters.setPreviewSize(mPreviewSize.width, mPreviewSize.height);
//set picture size based on device screen
parameters.setPictureSize(mPictureSize.width, mPictureSize.height);
//set output camera mode
parameters.setPictureFormat(PixelFormat.JPEG);
//set focous mode
parameters.setFocusMode(FOCUS_MODE_AUTO);
//set flash mode
parameters.setFlashMode("auto");
List<int[]> fps = parameters.getSupportedPreviewFpsRange();
//System.out.println("FPS size: " +fps.size());
//System.out.println("MAX FPS:"+(fps.get(fps.size()-1)[1])/1000);
//log min and max camera supported fps
Log.d("CAMERA", "CAMERA MAX FPS: "+(fps.get(fps.size()-1)[1])/1000);
Log.d("CAMERA", "CAMERA MIN FPS: "+(fps.get(fps.size()-1)[0])/1000);
if(camera_fps)
{
parameters.setPreviewFpsRange(fps.get(fps.size()-1)[1], fps.get(fps.size()-1)[1]);
}
//set camera parameters
camera.setParameters(parameters);
Toast.makeText(getApplicationContext(), "Your device are capable of previewing @" + fps.get(fps.size()-1)[1]/1000+"fps!",Toast.LENGTH_SHORT).show();
return camera; // returns null if camera is unavailable
}
关于如何解决这个问题的任何想法？
答案 0 :(得分：144)
我遇到了同样的问题。 mCamera.setPreviewCallback(null);没有帮助。在我的活动中，我已将其添加到releaseCamera：
mPreview.getHolder().removeCallback(mPreview);
现在有效。
答案 1 :(得分：20)
@ ookami.kb解决方案也适用于我，以及@srunni评论。
public void onPause() {
super.onPause();
if (mCamera != null) {
mCamera.setPreviewCallback(null);
mPreview.getHolder().removeCallback(mPreview);
mCamera.release();
}
}
我也删除了onDestroy方法。
答案 2 :(得分：10)
文档明确指出camera.release()会释放所有相机资源。此呼叫后，摄像机参考不能再使用了。
如果您想再次使用相机，则必须通过open(int)方法获取相机。
所有这些都在camera docs中进行了描述。
答案 3 :(得分：5)
要正确恢复，您需要执行以下操作：
@Override
public void onResume() {
super.onResume();
// Get the Camera instance as the activity achieves full user focus
if (mCamera == null) {
initializeCamera(); // Local method to handle camera initialization
}
}
protected void initializeCamera(){
// Get an instance of Camera Object
mCamera = getCameraInstance();
// create a basic camera preview class that can be included in a View layout.
mPreview=new CameraPreview(this,mCamera);
//add your preview class to the FrameLayout element.
preview.addView(mPreview);
//Trigger capturing an image by calling the Camera.takePicture() method.
captureButton.setOnClickListener(
new View.OnClickListener() {
@Override
public void onClick(View v) {
// get an image from the camera
mCamera.takePicture(null, null, mPicture);
}
}
);
}
还要提醒一下，除了定义FrameLayout预览和Button captureButton之外，oncreate（）什么也不做。
答案 4 :(得分：2)
@Override public void surfaceDestroyed(SurfaceHolder surfaceHolder) {
this.getHolder().removeCallback(this);
mCamera.stopPreview();
mCamera.release();
mCamera = null;
Log.e("surfaceDestroyed", "surfaceDestroyed");
}
然后在Resume功能上重新初始化相机。
答案 5 :(得分：1)
添加到okambi的答案。
这是在你恢复时搞乱一切的功能：
public void surfaceCreated(SurfaceHolder holder) {
// The Surface has been created, now tell the camera where to draw the preview.
try {
mCamera.setPreviewDisplay(holder);
mCamera.startPreview();
} catch (IOException e) {
Log.d(TAG, "Error setting camera preview: " + e.getMessage());
}
}
try {}没有捕获抛出的异常。即mCamera不存在，然后当它试图调用setPreviewDisplay（holder）时，就会发生崩溃。
因此，通过删除回调，不会调用此surfaceCreated并避免崩溃。
这是非常糟糕的Google文档。
答案 6 :(得分：0)
我遇到同样的问题，我修好了 - 在预览类的 surfaceDestroyed（SurfaceHolder holder）方法中添加 mCamera = null; 。
public void surfaceDestroyed(SurfaceHolder holder) {
// Surface will be destroyed when we return, so stop the preview.
if (mCamera != null) {
mCamera.stopPreview();
mCamera.release();
mCamera = null;
}
}
和 - 添加
camera = Camera.open();
camera.startPreview();
params = camera.getParameters();
preview.setCamera(camera);
在我的CameraActivity的 OnResume（）方法中。
答案 7 :(得分：0)
如果你有：
尝试调用虚方法'void android.hardware.Camera.setPreviewCallback（android.hardware.Camera $ PreviewCallback）” 在空对象引用上
我同意@ ookami.kb - mCamera.setPreviewCallback(null);是不够的，在它背后还添加了这个：
mCameraView.getHolder().removeCallback(mCameraView);
答案 8 :(得分：0)
我已经把
mPreview.getHolder().removeCallback(mPreview);
之间。
mCamera.setPreviewCallback(null);
和
mCamera.release();
它对我有用。
@Override
protected void onPause() {
super.onPause();
this.saveTextEdits();
try {
mCamera.stopPreview();
mCamera.setPreviewCallback(null);
**mPreview.getHolder().removeCallback(mPreview);**
mCamera.release();
mCamera = null;
}catch (Exception e){
}
}