private void checkWriteStoragePermission() {
    //FROM AN ACTIVITY
    if (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
        ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, MY_PERMISSIONS_REQUEST_WRITE_EXTERNAL_STORAGE);
    }
    
    //FROM A FRAGMENT
    if (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
        FragmentCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, MY_PERMISSIONS_REQUEST_WRITE_EXTERNAL_STORAGE);
    }
}

@Override
public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
    switch (requestCode) {
        case MY_PERMISSIONS_REQUEST_WRITE_EXTERNAL_STORAGE: {
            if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                //Do whatever with the permission granted
            } else {
                // permission denied, boo! Disable the
                // functionality that depends on this permission.
            }
            return;
        }
        default:
            super.onRequestPermissionsResult(requestCode, permissions, grantResults);
            break;

    }

}