从Stopped返回时,Android Simple Camera Control应用程序崩溃(Android Simple Camera Control App crashes when returning from Stopped)
我正在通过developer.Android教程构建相机应用程序,但我总是遇到以下问题:当我的应用程序被放入后台时,即根据活动生命周期停止,我尝试返回它崩溃,告诉我已经停止了工作。
我搜索了其他问题,但他们似乎都没有同样的问题,或者我无法识别它。
我试图找出发生此错误的最小代码量。 (仅限)活动:
public class CameraActivity extends ActionBarActivity { private Camera mCamera; private CameraPreview mPreview; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_camera_layout); // if device hardware has a camera if (checkCameraHardware(this)) // Create an instance of Camera mCamera = getCameraInstance(); // Create our Preview view and set it as the content of our activity. mPreview = new CameraPreview(this, mCamera); FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview); preview.addView(mPreview); } /** Check if this device has a camera */ private boolean checkCameraHardware(Context context) { if (context.getPackageManager().hasSystemFeature(PackageManager.FEATURE_CAMERA)){ // this device has a camera return true; } else { // no camera on this device return false; } } /** A safe way to get an instance of the Camera object. */ public static Camera getCameraInstance(){ Camera c = null; try { c = Camera.open(); // attempt to get a Camera instance } catch (Exception e){ // Camera is not available (in use or does not exist) } return c; // returns null if camera is unavailable } @Override public void onPause() { super.onPause(); releaseCamera(); // release the camera immediately on pause event } private void releaseCamera(){ if (mCamera != null){ mCamera.stopPreview(); // stop the preview mCamera.release(); // release the camera for other applications mCamera = null; } } @Override public void onResume() { super.onResume(); if (mCamera == null) mCamera = getCameraInstance(); } }
使用此类实例化CameraPreview:
public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback { private SurfaceHolder mHolder; private Camera mCamera; public CameraPreview(Context context, Camera camera) { super(context); mCamera = camera; // Install a SurfaceHolder.Callback so we get notified when the // underlying surface is created and destroyed. mHolder = getHolder(); mHolder.addCallback(this); // deprecated setting, but required on Android versions prior to 3.0 mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS); } 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("PandaHero", "Error setting camera preview: " + e.getMessage()); } } public void surfaceDestroyed(SurfaceHolder holder) { // empty. Take care of releasing the Camera preview in your activity. } public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) { // .. same as in the example of the link } }
至于错误消息,它总是告诉我在release()之后调用surfaceCreated()。 这让我觉得我必须错过一些重要的相机重新实现或预览某处。 我试图停止预览并在surfaceDestroyed(),onStop()中释放相机,并重新打开onStart()内部的预览,但错误仍然存在。 此外,如果我不首先包含预览,则不会发生崩溃(但我的用户也无法看到它,所以这是没有选择)。
所以,是的,我认为在利用生命周期方面,我在这里缺少一些重要的东西。
编辑:我提到的错误消息。
03-02 14:33:45.553 15462-15462/com.example.vrevru.viewlate_camerasetupsimple E/AndroidRuntime﹕ FATAL EXCEPTION: main java.lang.RuntimeException: Method called after release() at android.hardware.Camera.setPreviewDisplay(Native Method) at android.hardware.Camera.setPreviewDisplay(Camera.java:428) at com.example.thorsten.viewlate_camerasetupsimple.CameraPreview.surfaceCreated(CameraPreview.java:32) at android.view.SurfaceView.updateWindow(SurfaceView.java:639) at android.view.SurfaceView.onWindowVisibilityChanged(SurfaceView.java:262) at android.view.View.dispatchWindowVisibilityChanged(View.java:7440) at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1042) at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1042) at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1042) at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1042) at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1042) at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1042) at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1042) at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1237) at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1009) at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4236) at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725) at android.view.Choreographer.doCallbacks(Choreographer.java:555) at android.view.Choreographer.doFrame(Choreographer.java:525) at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711) at android.os.Handler.handleCallback(Handler.java:615) at android.os.Handler.dispatchMessage(Handler.java:92) at android.os.Looper.loop(Looper.java:137) at android.app.ActivityThread.main(ActivityThread.java:4872) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:511) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:790) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557) at dalvik.system.NativeStart.main(Native Method)
I was working through the developer.Android Tutorials on building a Camera App but I always encounter the following problem: When my app is put into the background, i.e. Stopped according to the activity lifecycle, and I try to return to it it crashes, telling me the App has stopped working.
I searched other questions, but none of them seemed to have this same problem or I wasn't able to recognise it.
I tried to figure out the minimum amount of code for this error to occur. The (only) Activity:
public class CameraActivity extends ActionBarActivity { private Camera mCamera; private CameraPreview mPreview; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_camera_layout); // if device hardware has a camera if (checkCameraHardware(this)) // Create an instance of Camera mCamera = getCameraInstance(); // Create our Preview view and set it as the content of our activity. mPreview = new CameraPreview(this, mCamera); FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview); preview.addView(mPreview); } /** Check if this device has a camera */ private boolean checkCameraHardware(Context context) { if (context.getPackageManager().hasSystemFeature(PackageManager.FEATURE_CAMERA)){ // this device has a camera return true; } else { // no camera on this device return false; } } /** A safe way to get an instance of the Camera object. */ public static Camera getCameraInstance(){ Camera c = null; try { c = Camera.open(); // attempt to get a Camera instance } catch (Exception e){ // Camera is not available (in use or does not exist) } return c; // returns null if camera is unavailable } @Override public void onPause() { super.onPause(); releaseCamera(); // release the camera immediately on pause event } private void releaseCamera(){ if (mCamera != null){ mCamera.stopPreview(); // stop the preview mCamera.release(); // release the camera for other applications mCamera = null; } } @Override public void onResume() { super.onResume(); if (mCamera == null) mCamera = getCameraInstance(); } }
The CameraPreview is instantiated using this class:
public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback { private SurfaceHolder mHolder; private Camera mCamera; public CameraPreview(Context context, Camera camera) { super(context); mCamera = camera; // Install a SurfaceHolder.Callback so we get notified when the // underlying surface is created and destroyed. mHolder = getHolder(); mHolder.addCallback(this); // deprecated setting, but required on Android versions prior to 3.0 mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS); } 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("PandaHero", "Error setting camera preview: " + e.getMessage()); } } public void surfaceDestroyed(SurfaceHolder holder) { // empty. Take care of releasing the Camera preview in your activity. } public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) { // .. same as in the example of the link } }
As for error messages, it always shows me that surfaceCreated() is called after release(). This made me think that I have to be missing some important reinstantiation of the camera or preview somewhere. I tried to stop the preview and release the camera within surfaceDestroyed(), onStop() and also to reopen the preview inside onStart() but the error persisted. Also, no crashes occur if I do not include the Preview in the first place (but then my users wouldn't be able to see it either, so that's no option).
So yeah, I think there is something vital I am missing here in terms of making use of the life cycle.
Edit: The Error message I mentioned.
03-02 14:33:45.553 15462-15462/com.example.vrevru.viewlate_camerasetupsimple E/AndroidRuntime﹕ FATAL EXCEPTION: main java.lang.RuntimeException: Method called after release() at android.hardware.Camera.setPreviewDisplay(Native Method) at android.hardware.Camera.setPreviewDisplay(Camera.java:428) at com.example.thorsten.viewlate_camerasetupsimple.CameraPreview.surfaceCreated(CameraPreview.java:32) at android.view.SurfaceView.updateWindow(SurfaceView.java:639) at android.view.SurfaceView.onWindowVisibilityChanged(SurfaceView.java:262) at android.view.View.dispatchWindowVisibilityChanged(View.java:7440) at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1042) at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1042) at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1042) at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1042) at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1042) at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1042) at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1042) at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1237) at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1009) at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4236) at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725) at android.view.Choreographer.doCallbacks(Choreographer.java:555) at android.view.Choreographer.doFrame(Choreographer.java:525) at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711) at android.os.Handler.handleCallback(Handler.java:615) at android.os.Handler.dispatchMessage(Handler.java:92) at android.os.Looper.loop(Looper.java:137) at android.app.ActivityThread.main(ActivityThread.java:4872) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:511) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:790) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557) at dalvik.system.NativeStart.main(Native Method)
原文:https://stackoverflow.com/questions/28812006