我正在尝试在Android上制作相机应用程序，Log-cat中没有错误但是当我按下后退按钮时应用程序没有关闭;如果我想在停止后打开另一个应用程序相机;相机被锁定!!任何提示或想法？ 提前谢谢。
public class Capture extends Activity {
private Camera mCamera;
private ViewCamera mPreview;
public static final int MEDIA_TYPE_IMAGE = 1;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.camera);
releaseCamera();
// Create an instance of Camera
mCamera = getCameraInstance();
Log.d("EyeSeeJD", "getCameraInstance");
// Create our Preview view and set it as the content of our activity.
mPreview = new ViewCamera(this, mCamera);
FrameLayout preview = (FrameLayout) findViewById(R.id.frame);
Log.d("EyeSeeJD", "addview ");
preview.addView(mPreview);
}
/** 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
// c.lock();
} catch (Exception e) {
// Camera is not available (in use or does not exist)
Log.d("EyeSeeJD", "can't open camera ");
}
return c; // returns null if camera is unavailable
}
/** Create a File for saving an image or video */
private static File getOutputMediaFile(int type) {
// To be safe, you should check that the SDCard is mounted
// using Environment.getExternalStorageState() before doing this.
File mediaStorageDir = new File(
Environment
.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES),
"MyCameraApp");
// This location works best if you want the created images to be shared
// between applications and persist after your app has been uninstalled.
// Create the storage directory if it does not exist
if (!mediaStorageDir.exists()) {
if (!mediaStorageDir.mkdirs()) {
Log.d("MyCameraApp", "failed to create directory");
return null;
}
}
// Create a media file name
String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss")
.format(new Date());
File mediaFile;
if (type == MEDIA_TYPE_IMAGE) {
mediaFile = new File(mediaStorageDir.getPath() + File.separator
+ "IMG_" + timeStamp + ".jpg");
} else {
return null;
}
return mediaFile;
}
private PictureCallback mPicture = new PictureCallback() {
@Override
public void onPictureTaken(byte[] data, Camera camera) {
File pictureFile = getOutputMediaFile(MEDIA_TYPE_IMAGE);
if (pictureFile == null) {
Log.d("EyeSeeJD",
"Error creating media file, check storage permissions ");
return;
}
try {
FileOutputStream fos = new FileOutputStream(pictureFile);
fos.write(data);
fos.close();
} catch (FileNotFoundException e) {
Log.d("EyeSeeJD", "File not found: " + e.getMessage());
} catch (IOException e) {
Log.d("EyeSeeJD", "Error accessing file: " + e.getMessage());
}
}
};
@Override
protected void onResume() {
super.onResume();
/*
* if (mCamera == null) { releaseCamera(); // release the camera
* immediately on pause event System.exit(0); }
*/
}
@Override
protected void onPause() {
super.onPause();
releaseCamera(); // release the camera immediately on pause event
// System.exit(0);
}
private void releaseCamera() {
if (mCamera != null) {
mCamera.stopPreview();
mCamera.setPreviewCallback(null);
mPreview.getHolder().removeCallback(mPreview);
// mCamera.unlock();
mCamera.release(); // release the camera for other applications
mCamera = null;
}
}
@Override
public void onBackPressed() { // TODO Auto-generated methodstub
super.onBackPressed();
//mCamera.setPreviewCallback(null);
//mPreview.getHolder().removeCallback(mPreview);
mCamera.stopPreview();
mCamera.release(); // release the camera for other applications
mCamera = null;
finish();
System.exit(0);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
// TODO Auto-generated method stub
//mCamera.setPreviewCallback(null);
mCamera.takePicture(null, null, mPicture);
//mCamera.release();
// mCamera.startPreview();
return super.onTouchEvent(event);
}
@Override
protected void onDestroy() {
// TODO Auto-generated method stub
super.onDestroy();
mCamera.stopPreview();
mCamera.setPreviewCallback(null);
mPreview.getHolder().removeCallback(mPreview);
mCamera.release(); // release the camera for other applications
mCamera = null;
finish();
System.exit(0);
}
}
ViewCamera.java
public class ViewCamera extends SurfaceView implements SurfaceHolder.Callback {
private SurfaceHolder mHolder = null;
private Camera mCamera = null;
public ViewCamera(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);
mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
}
@Override
public void surfaceCreated(SurfaceHolder holder) {
// TODO Auto-generated method stub
// 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("EyeSeeJD", "Error setting camera preview: " + e.getMessage());
}
}
// check if device has camera
private boolean checkCameraHardware(Context context) {
if (context.getPackageManager().hasSystemFeature(
PackageManager.FEATURE_CAMERA)) {
// this device has a camera
Log.d("EyeSeeJd", "there is a camera ");
return true;
} else {
// no camera on this device
Log.d("EyeSeeJd", "there is no camera ");
return false;
}
}
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
// TODO Auto-generated method stub
// If your preview can change or rotate, take care of those events here.
// Make sure to stop the preview before resizing or reformatting it.
if (mHolder.getSurface() == null) {
// preview surface does not exist
return;
}
// stop preview before making changes
try {
mCamera.stopPreview();
} catch (Exception e) {
// ignore: tried to stop a non-existent preview
}
// set preview size and make any resize, rotate or
// reformatting changes here
/*Camera.Parameters parameters = mCamera.getParameters();
parameters.setPreviewSize(320, 480);
mCamera.setParameters(parameters);*/
// start preview with new settings
try {
mCamera.setPreviewDisplay(mHolder);
mCamera.startPreview();
// mCamera.unlock();
} catch (Exception e) {
Log.d("EyeSeeJd",
"Error starting camera preview: " + e.getMessage());
}
}
@Override
public void surfaceDestroyed(SurfaceHolder arg0) {
// TODO Auto-generated method stub
// empty. Take care of releasing the Camera preview in your activity.
this.getHolder().removeCallback(this);
mCamera.stopPreview();
mCamera.release();
mCamera = null;
}
}
答案 0 :(得分：0)
如果不在调试器中关注代码，很难说出真正发生了什么，但有可能会多次调用Camera.release()。某处可能有NullPointerExeception阻止正常关机。您的应用中应该只有一个版本，onPause()是拨打releaseCamera()的理想场所。我不明白为什么你需要覆盖onBackPressed()，不建议从此覆盖调用finish()，并且更多地调用System.exit()。另外，我会将来电转至getCameraInstance()至onResume()或致onStart()。
答案 1 :(得分：0)
你的应用程序在按下时需要时间关闭的原因是你的应用程序崩溃了，因为在onBackPressed（）方法中你将mCamera设置为null，而在onDestroy（）中你再次使用它来停止和释放相机。