当我切换相机时，此错误显示"调用Camera.release()后正在使用java.lang.RuntimeException:相机"。我释放相机的方式不正确吗？有人可以建议我实现它的最佳方法吗？
这是我的相机活动.java：
private Camera mCamera;
private CameraPreviewActivity mPreview;
private int cameraId = 0;
private static final int MY_PERMISSIONS_REQUEST_CAMERA = 1;
/**
* 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.
*/
// attempt to get a Camera instance
public static Camera getCameraInstance() {
Camera c = null;
try {
c = Camera.open();
} catch (Exception e) {
System.out.println("Camera not working.");
}
return c; // returns null if camera is unavailable
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.camerapreview_activity);
// Create our Preview view and set it as the content of our activity.
// Create an instance of Camera
switchCamera();
showCamera();
}
public void switchCamera() {
ToggleButton facingSwitch = (ToggleButton) findViewById(R.id.facingSwitch);
facingSwitch.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
onDestroy();
preview.removeAllViews();
if (isChecked) {
// The toggle is enabled
preview.addView(mPreview);
Camera.open(Camera.CameraInfo.CAMERA_FACING_FRONT);
} else {
// The toggle is disabled
preview.addView(mPreview);
Camera.open(Camera.CameraInfo.CAMERA_FACING_BACK);
}
}
});
}
protected void onDestroy () {
super.onDestroy();
if (mCamera != null){
mCamera.stopPreview();
mCamera.release(); // release the camera for other applications
mCamera = null;
}
}
public void showCamera() {
if (ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
// Permission is not granted
// Should we show an explanation?
if (ActivityCompat.shouldShowRequestPermissionRationale(this,
Manifest.permission.CAMERA)) {
Toast.makeText(this, "Camera permission is needed to show the camera preview", Toast.LENGTH_SHORT).show();
// Show an explanation to the user *asynchronously* -- don't block
// this thread waiting for the user's response! After the user
// sees the explanation, try again to request the permission.
} else {
// No explanation needed; request the permission
ActivityCompat.requestPermissions(this,
new String[]{Manifest.permission.CAMERA},
MY_PERMISSIONS_REQUEST_CAMERA);
// MY_PERMISSIONS_REQUEST_READ_CONTACTS is an
// app-defined int constant. The callback method gets the
// result of the request.
}
}
else {
// Permission has already been granted
mCamera = getCameraInstance();
mPreview = new CameraPreviewActivity(this, mCamera);
FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
preview.addView(mPreview);
}
}
// Here, thisActivity is the current activity
@Override
public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) {
switch (requestCode) {
case MY_PERMISSIONS_REQUEST_CAMERA: {
// If request is cancelled, the result arrays are empty.
if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
// Create our Preview view and set it as the content of our activity.
// permission was granted, yay! Do the
// contacts-related task you need to do.
showCamera();
} else {
Toast.makeText(this, "Permission was not granted", Toast.LENGTH_SHORT).show();
// permission denied, boo! Disable the
// functionality that depends on this permission.
}
return;
}
}
}
// other 'case' lines to check for other
// permissions this app might request.
这是我的相机预览活动.java
private SurfaceHolder mHolder;
private Camera mCamera;
public CameraPreviewActivity(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(TAG, "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) {
// 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
// start preview with new settings
try {
mCamera.setPreviewDisplay(mHolder);
mCamera.startPreview();
} catch (Exception e){
Log.d(TAG, "Error starting camera preview: " + e.getMessage());
}
}
}
Camera.open（
1） 和 Camera.open（0） 返回一个相机实例，使用它来替换 mCamera。这并不能解释运行时异常。
发生此异常的原因是，您的 CameraPreviewActivity 保留了对您在 CameraActivity 中打开的 Camera 实例的单独引用。
最佳做法是仅将引用保留在 CameraPreviewActivity 类中，并从 CameraActivity 类中删除 mCamera 字段。