安卓相机权限

Question

我有这段代码，是我使用官方开发者 android 网站制作的。我想创建相机预览，但首先请求权限。当我启动应用程序时，他们崩溃了，但在应用程序退出之前，他们要求我授予我授予的权限，然后应用程序崩溃。在我再次进入应用程序后它工作得很好，但我想摆脱那个崩溃。有人知道解决办法吗？

CameraActivity.java

public class CameraActivity extends AppCompatActivity {

    private Camera mCamera;
    private CameraPreview mPreview;
    private static final int PERMISSION_CAMERA = 1;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_camera);

        if (ContextCompat.checkSelfPermission(this,
                Manifest.permission.CAMERA)
                != PackageManager.PERMISSION_GRANTED) {

            // Should we show an explanation?
            if (ActivityCompat.shouldShowRequestPermissionRationale(this,
                    Manifest.permission.CAMERA)) {

                // 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, we can request the permission.

                ActivityCompat.requestPermissions(this,
                        new String[]{Manifest.permission.CAMERA},
                        PERMISSION_CAMERA);

                // MY_PERMISSIONS_REQUEST_READ_CONTACTS is an
                // app-defined int constant. The callback method gets the
                // result of the request.
            }
        }

        // 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);
    }

    @Override
    public void onRequestPermissionsResult(int requestCode,
                                           String permissions[], int[] grantResults) {
        switch (requestCode) {
            case PERMISSION_CAMERA: {
                // If request is cancelled, the result arrays are empty.
                if (grantResults.length > 0
                        && grantResults[0] == PackageManager.PERMISSION_GRANTED) {

                    // permission was granted, yay! Do the
                    // contacts-related task you need to do.

                } else {

                    // permission denied, boo! Disable the
                    // functionality that depends on this permission.
                }
                return;
            }

            // other 'case' lines to check for other
            // permissions this app might request.
        }
    }

    @Override
    public void onPause() {
        super.onPause();
        // Stop camera access
        releaseCamera();
    }

    /** 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
    }

    private void releaseCamera(){
        if (mCamera != null){
            mCamera.release();        // release the camera for other applications
            mCamera = null;
        }
    }
}

Logcat

FATAL EXCEPTION: main
Process: com.example.ivan.cameratest1, PID: 7690
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.hardware.Camera.setPreviewDisplay(android.view.SurfaceHolder)' on a null object reference
at com.example.ivan.cameratest1.CameraPreview.surfaceCreated(CameraPreview.java:36)
at android.view.SurfaceView.updateWindow(SurfaceView.java:656)
at android.view.SurfaceView$3.onPreDraw(SurfaceView.java:172)
at android.view.ViewTreeObserver.dispatchOnPreDraw(ViewTreeObserver.java:1013)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2542)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1537)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7183)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:959)
at android.view.Choreographer.doCallbacks(Choreographer.java:734)
at android.view.Choreographer.doFrame(Choreographer.java:670)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:945)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6776)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1496)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1386)

Answer 1

private final String TAG = "Debug_MainActivity";
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    checkCameraPermission();
}


private final int MY_PERMISSIONS_REQUEST_USE_CAMERA = 0x00AF;
private void checkCameraPermission(){
    if (ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA ) != PackageManager.PERMISSION_GRANTED) {
        Log.d(TAG,"Permission not available requesting permission");
            ActivityCompat.requestPermissions(this,
                                                new String[]{Manifest.permission.CAMERA}, MY_PERMISSIONS_REQUEST_USE_CAMERA);
    } else {
        Log.d(TAG,"Permission has already granted");
    }
}


@Override
public void onRequestPermissionsResult(int requestCode,
                                       String permissions[], int[] grantResults) {
    switch (requestCode) {
        case MY_PERMISSIONS_REQUEST_USE_CAMERA: {
            // If request is cancelled, the result arrays are empty.
            if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                Log.d(TAG,"permission was granted! Do your stuff");
            } else {
                Log.d(TAG,"permission denied! Disable the function related with permission.");
            }
            return;
        }
    }
}

Answer 2

我认为您在获得权限时遇到了错误。即使您没有权限，您也试图打开相机。这就是为什么它在第一次启动而不是在第二次启动时崩溃。

尝试执行以下更改（我更改了onCreate 和onRequestPermissionsResult）：

public class CameraActivity extends AppCompatActivity {

    private Camera mCamera;
    private CameraPreview mPreview;
    private static final int PERMISSION_CAMERA = 1;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_camera);

        if (ContextCompat.checkSelfPermission(this,
                Manifest.permission.CAMERA)
                != PackageManager.PERMISSION_GRANTED) {

            ActivityCompat.requestPermissions(this,
                    new String[]{Manifest.permission.CAMERA},
                    PERMISSION_CAMERA);
            }
        } else {
            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);
    }

    @Override
    public void onRequestPermissionsResult(int requestCode,
                                           String permissions[], int[] grantResults) {
        switch (requestCode) {
            case PERMISSION_CAMERA: {
                if (grantResults.length > 0
                        && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    mCamera = getCameraInstance();
                }
                return;
            }
        }
    }

    ...
}