Question

I am developing an Android app, this app has a dozen of Activities, each one is for a corresponding screen. Now I have this common subtitle bar on top of the screens.
this subtitle bar has a button to display an alert dialog which shows link list to go to a different screen.

I could write a same function for each activity to call the alert dialog, but that would be tedious if I want to modify them, so I created this class:

public class MenuAlertDialog extends Activity {

/*
@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
}
 */
public void createMenu(final Context context){
    AlertDialog.Builder dlg = new AlertDialog.Builder(context);
    dlg.setTitle("menu");

    String[] items = {"pageA", "pageB", "pageC", "pageD", "pageE"};
    dlg.setItems(items, new DialogInterface.OnClickListener(){
        @Override
        public void onClick(DialogInterface dialog, int which){
            switch(which){
            case 0:
                Intent intent = new Intent(context, MainActivity.class);
                startActivity(intent);
                break;
            default:
                break;

            }
        }
    });
    dlg.show();
}
}

and call it from each activity, like this:

MenuAlertDialog menu = new MenuAlertDialog();
menu.createMenu(this);

from inside of onCreate.

It can display the alertDialog, but whenever I press pageA link, it fails with an unexpected error.

Logcat says its a nullpointererror and the cause seems

startActivity(intent);

What am I doing wrong?

Answer 1

Remove the code

extends Activity

as you have no need to extend your class that you are creating since it does not rely on any activity related functionality.

Where you call startActivity(intent); replace it with

context.startActivity(intent);