Android Simple Camera Control App 从 Stopped 返回时崩溃
Android Simple Camera Control App crashes when returning from Stopped
我正在学习 building a Camera App 上的 developer.Android 教程，但我总是遇到以下问题：当我的应用程序进入后台时，即根据 activity 生命周期停止，然后我尝试 return 它崩溃了，告诉我应用程序已停止工作。
我搜索了其他问题，但其中 none 个似乎有同样的问题，或者我无法识别。
我试图找出发生此错误的最少代码量。
（仅）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();
}
}
CameraPreview 是使用 class:
实例化的
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()之后调用了surfaceCreated()。这让我觉得我必须错过一些重要的相机重新实例化或某处预览。我试图在 surfaceDestroyed()、onStop() 中停止预览并释放相机，并在 onStart() 中重新打开预览，但错误仍然存在。
此外，如果我首先不包含预览版，则不会发生崩溃（但我的用户也将无法看到它，所以这不是选择）。
是的，我认为在利用生命周期方面我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)
好的，
我想我找到了解决方案，尽管我不确定这是最好的解决方案。
我注意到我从未告诉我的应用程序在 onPause() 中发布旧预览后创建新预览。我认为 Android 会处理这个问题，因为文档总是声明不需要重做导致首次创建应用程序的任何设置。显然，我误解了他们（尽管他们的意思是什么？）。
所以我在 onPause() 中添加了从我的 Framelayout 中手动删除旧的 CameraPreview 对象，然后创建一个新对象并将其添加到 onResume() 中的 Framelayout。
@Override
public void onPause() {
super.onPause();
releaseCamera(); // release the camera immediately on pause event
// two new lines for removing the old CameraPreview
FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
preview.removeView(mPreview);
}
@Override
public void onResume() {
super.onResume();
if (mCamera == null)
{
mCamera = getCameraInstance();
// three new lines, creating a new CameraPreview, then adding it to the FrameLayout
mPreview = new CameraPreview(this, mCamera);
FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
preview.addView(mPreview);
}
}
然而，虽然现在错误已经消失并且我的问题已解决（应用程序不再崩溃），但我只是将一些看似非常昂贵的代码行放入我的暂停和恢复函数中。到其他应用程序的转换和返回的速度明显减慢。有没有更智能的方法来做到这一点？
我正在学习 building a Camera App 上的 developer.Android 教程，但我总是遇到以下问题：当我的应用程序进入后台时，即根据 activity 生命周期停止，然后我尝试 return 它崩溃了，告诉我应用程序已停止工作。
我搜索了其他问题，但其中 none 个似乎有同样的问题，或者我无法识别。
我试图找出发生此错误的最少代码量。 （仅）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();
}
}
CameraPreview 是使用 class:
实例化的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()之后调用了surfaceCreated()。这让我觉得我必须错过一些重要的相机重新实例化或某处预览。我试图在 surfaceDestroyed()、onStop() 中停止预览并释放相机，并在 onStart() 中重新打开预览，但错误仍然存在。 此外，如果我首先不包含预览版，则不会发生崩溃（但我的用户也将无法看到它，所以这不是选择）。
是的，我认为在利用生命周期方面我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)
好的，
我想我找到了解决方案，尽管我不确定这是最好的解决方案。
我注意到我从未告诉我的应用程序在 onPause() 中发布旧预览后创建新预览。我认为 Android 会处理这个问题，因为文档总是声明不需要重做导致首次创建应用程序的任何设置。显然，我误解了他们（尽管他们的意思是什么？）。
所以我在 onPause() 中添加了从我的 Framelayout 中手动删除旧的 CameraPreview 对象，然后创建一个新对象并将其添加到 onResume() 中的 Framelayout。
@Override
public void onPause() {
super.onPause();
releaseCamera(); // release the camera immediately on pause event
// two new lines for removing the old CameraPreview
FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
preview.removeView(mPreview);
}
@Override
public void onResume() {
super.onResume();
if (mCamera == null)
{
mCamera = getCameraInstance();
// three new lines, creating a new CameraPreview, then adding it to the FrameLayout
mPreview = new CameraPreview(this, mCamera);
FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
preview.addView(mPreview);
}
}
然而，虽然现在错误已经消失并且我的问题已解决（应用程序不再崩溃），但我只是将一些看似非常昂贵的代码行放入我的暂停和恢复函数中。到其他应用程序的转换和返回的速度明显减慢。有没有更智能的方法来做到这一点？