change Main UI from custom Dialog Class

Question

I have 2 class, Main and DialogOrder

Main

public class Main extends Fragment{
ImageView order;


@Override
public View onCreateView(LayoutInflater inflater, final ViewGroup container, Bundle savedInstanceState) {

     order.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

               new DialogOrder(getActivity()).show();
            }
        });

  return view;
  }
  public void init(Bundle savedInstanceState) {   
   order = (ImageView) view.findViewById(R.id.order);
   order.setImageResource(R.drawable.orderd);
   RelativeLayout.LayoutParams orderparams = new RelativeLayout.LayoutParams(Main.screenHeight / 8, Main.screenHeight / 8);
   orderparams.addRule(RelativeLayout.ALIGN_PARENT_BOTTOM);
   orderparams.addRule(RelativeLayout.CENTER_HORIZONTAL);
    orderparams.setMargins(Main.screenHeight / 80, Main.screenHeight / 80, Main.screenHeight / 80, Main.screenHeight / 30);

    order.setLayoutParams(orderparams);


 }

  public void update_UI(){

    order.setVisibility(View.INVISIBLE);

}

}

DialogOrder

public class DialogOrder extends Dialog {
Button button;
Main main;
Activity context;


public DialogOrder(Activity context) {
    super(context);

    this.context = context;
}

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
    requestWindowFeature(Window.FEATURE_NO_TITLE);
 setContentView(R.layout.order_dialog);
 main = new Main();
 button = (Button)findviewbyid(R.id.bd);

 button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

           main.update_UI();
           dismiss();
        }
    });
}}

what I want is to set order image INVISIBLE when the user press the button on dialog right now the code give me java.lang.NullPointerException

probably I try update the UI wrong so please can someone tell me what the right way to update parent UI class from child class ?

Answer 1

You can update your main fragment by passing it to Dialog constructor or you can use Listener/Callback to communicate between your main fragment and dialog.

The best practice is is using Listener/Callback because a Dialog should not have access to the caller. This is also decouple Dialog from Main fragment.

First, create the listener via interface in the dialog:

public class DialogOrder extends Dialog {
  ...
  Activity context;
  private DialogListener listener;

  public interface DialogListener {
    void onButtonClicked();
  }

  public DialogOrder(Activity context, DialogListener listener) {
    super(context);
    this.context = context;
    this.listener = listener;
  }

  ...

}

Then, when button click call the listener:

public class DialogOrder extends Dialog {

  Activity context;
  private DialogListener listener;

  public interface DialogListener {
    void onButtonClicked();
  }

  public DialogOrder(Activity context, DialogListener listener) {
    super(context);
    this.context = context;
    this.listener = listener;
  }

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    ...

    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
           listener.onButtonClicked();
           dismiss();
        }
    });
  }
}

Now, you can create the dialog with the listener. Something like this:

DialogOrder.DialogListener listener = new DialogOrder.DialogListener() {
   @Ovveride
   public void onButtonClicked() {
     update_UI();
   }
};

DialogOrder dialogOrder = new DialogOrder(getActivity(), listener);
dialogOder.show();

The main fragment will be listening for button clicked in the dialog.