Ask for external storage read and write permissions

AndroidManifest.xml

<!--

    <uses-permission android:name="android.permission.CAMERA" /> 
Add the following two lines below the line above -->
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

<!-- ... -->

MainActivity.java

//...
//public class MainActivity extends AppCompatActivity {
    static final Integer WRITE_EXST = 0x3;
    static final Integer READ_EXST = 0x4;
//  static final Integer CAMERA = 0x5;
//...
//...
// replace the whole ask-method with the following code:
    public boolean ask() {
        boolean answer = false;
        if (askForPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE, WRITE_EXST)) {
            if (askForPermission(Manifest.permission.READ_EXTERNAL_STORAGE, READ_EXST)) {
                if (askForPermission(Manifest.permission.CAMERA, CAMERA)) {
                    answer = true;
                }
            }
        } else {
            answer = false;
        }
        return answer;
    }
//...
//}