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import android.Manifest; import android.annotation.SuppressLint; import android.app.AlertDialog; import android.content.DialogInterface; import android.content.pm.PackageManager; import android.os.Bundle; import android.support.annotation.NonNull; import android.support.v4.app.ActivityCompat; import android.support.v4.content.ContextCompat; import android.support.v7.app.AppCompatActivity; import android.view.View; import android.widget.Button; import android.widget.Toast; public class MainActivity extends AppCompatActivity {     private static final int STORAGE_PERMISSION_CODE = 1;     private Button buttonRequest;     @SuppressLint("MissingInflatedId")     @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);         buttonRequest = findViewById(R.id.button_request);         buttonRequest.setOnClickListener(new View.OnClickListener() {             @Override             public void onClick(View view) {                 if (ContextCompat.checkSelfPermission(MainActivity.this, Manifest.permission.READ_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED) {                    Toast.makeText(MainActivity.this, "You have already granted the permission", Toast.LENGTH_SHORT).show();                 } else {                     requestStoragePermission();                 }             }         });     }     private void requestStoragePermission() {         if (ActivityCompat.shouldShowRequestPermissionRationale(MainActivity.this, Manifest.permission.READ_EXTERNAL_STORAGE)) {             new AlertDialog.Builder(MainActivity.this)                     .setTitle("Permission needed")                     .setMessage("This permission is needed to access the external storage")                     .setPositiveButton("OK", new DialogInterface.OnClickListener() {                         @Override                         public void onClick(DialogInterface dialog, int which) {                             ActivityCompat.requestPermissions(MainActivity.this, new String[] {Manifest.permission.READ_EXTERNAL_STORAGE}, STORAGE_PERMISSION_CODE);                        }                     })                     .setNegativeButton("Cancel", new DialogInterface.OnClickListener() {                         @Override                         public void onClick(DialogInterface dialog, int which) {                             dialog.dismiss();                         }                     })                     .create().show();         } else {             ActivityCompat.requestPermissions(MainActivity.this, new String[] {Manifest.permission.READ_EXTERNAL_STORAGE}, STORAGE_PERMISSION_CODE);        }     }     @Override     public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {         if (requestCode == STORAGE_PERMISSION_CODE) {             if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {                 Toast.makeText(this, "Permission granted", Toast.LENGTH_SHORT).show();             } else {                 Toast.makeText(this, "Permission not granted", Toast.LENGTH_SHORT).show();             }         }     }