如何从弹出窗口 window class 更改片段中的 ImageView？

Question

当我单击弹出窗口 window ZA2F635D0E0F3874FFF8B581C132E6C7A7Z 中的图像时，我想更改 ImageView

弹出 class

public class MoodPopUp extends Activity {

ImageView a,b,c,d,e,f,g,h,i;
ImageView main;

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.mood_picker_popup);

    DisplayMetrics  displayMetrics = new DisplayMetrics();
    getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);

    int width = displayMetrics.widthPixels;
    int height = displayMetrics.heightPixels;

    //Pop Up Window Size
    getWindow().setLayout((int) (width*.8),(int)(height*.6));

    //Set emoji images on mood imageview
    //Main Mood Image View
    main = (ImageView) findViewById(R.id.MainMoodimageview);

    //Pop Up Picker on Click
    a = (ImageView) findViewById(R.id.Aemoji);
    a.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            main.setImageResource(R.drawable.smiling);
        }
    });
}

这是来自另一个片段的 imageview，我想在点击时更改。

   <ImageView
    android:id="@+id/MainMoodimageview"
    android:layout_width="187dp"
    android:layout_height="163dp"
    android:layout_marginTop="19dp"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/divider3"
    android:src="@drawable/ic_baseline_emoji_emotions_24" />