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This is a part of QR Code scanner app. In the very beginning of the app it asks for camera permission, when i click to allow, app doesn't respond. but from second time, app works correctly. I think the error may be in checking permission. Please help me to find the mistake.

surfaceView.getHolder().addCallback(new SurfaceHolder.Callback() 
 @Override
 public void surfaceCreated(SurfaceHolder holder) 
 try 
 if (ActivityCompat.checkSelfPermission(MainActivity.this, Manifest.permission.CAMERA) == PackageManager.PERMISSION_GRANTED) 

 cameraSource.start(surfaceView.getHolder());
 else 
 ActivityCompat.requestPermissions(MainActivity.this, new
 StringManifest.permission.CAMERA, REQUEST_CAMERA_PERMISSION);
 

 catch (IOException e) 
 e.printStackTrace();
 

 

 @Override
 public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) 
 

 @Override
 public void surfaceDestroyed(SurfaceHolder holder) 
 cameraSource.stop();
 
 );

When your permission is given/denied, there is a callback method called, named onRequestPermissionsResult(int requestCode, String permissions, int grantResults).

The callback returns with the requestCode which was the code permission was called with first.

All you have to check

1. The requestCode equals to what permission you asked for




2. grandResult array is not empty




3. grantResults[0] is equal to PackageManager.PERMISSION_GRANTED

Example:

@Override
public void onRequestPermissionsResult(int requestCode, String permissions, int grantResults) 

 switch (requestCode) 
 case MY_PERMISSIONS_REQUEST: // here, MY_PERMISSIONS_REQUEST is the intended request code
 // If request is cancelled, the result arrays are empty.
 if (grantResults.length > 0
 && grantResults[0] == PackageManager.PERMISSION_GRANTED) 

 // permission was granted, yay! Do the 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