I have create custom dialog for permission:
if (ContextCompat.checkSelfPermission(context, Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
   if (ActivityCompat.shouldShowRequestPermissionRationale((Activity) context, Manifest.permission.READ_EXTERNAL_STORAGE)) {
       AlertDialog.Builder alertBuilder = new AlertDialog.Builder(context);
       alertBuilder.setCancelable(true);
       alertBuilder.setTitle("Permission necessary");
       alertBuilder.setMessage("External storage permission is necessary");
       alertBuilder.setPositiveButton(android.R.string.yes, new DialogInterface.OnClickListener() {
       @TargetApi(Build.VERSION_CODES.JELLY_BEAN)
       public void onClick(DialogInterface dialog, int which) {
           ActivityCompat.requestPermissions((Activity) context, new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, MY_PERMISSIONS_REQUEST_READ_EXTERNAL_STORAGE);}});
       AlertDialog alert = alertBuilder.create();
       alert.show();
   } else { 
          ActivityCompat.requestPermissions((Activity) context, new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, MY_PERMISSIONS_REQUEST_READ_EXTERNAL_STORAGE);}
    return false;} 
 else { 
     return true;
}
Hope this will help you :)