Popup Menu

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.application.popupproject.MainActivity">

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="showPopup"
        android:text="show popup"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">

    <item
        android:id="@+id/item1"
        android:title="Item 1" />

    <item
        android:id="@+id/item2"
        android:title="Item 2" />

    <item
        android:id="@+id/item3"
        android:title="Item 3" />

    <item
        android:id="@+id/item4"
        android:title="Item 4" />
    
</menu>

package com.example.application.popupproject;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.PopupMenu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity implements PopupMenu.OnMenuItemClickListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    public void showPopup(View v) {
        PopupMenu popup = new PopupMenu(this, v);
        popup.setOnMenuItemClickListener(this);
        popup.inflate(R.menu.popup_menu);
        popup.show();
    }


    @Override
    public boolean onMenuItemClick(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.item1:
                Toast.makeText(this, "Item 1 clicked", Toast.LENGTH_SHORT).show();
                return true;
            case R.id.item2:
                Toast.makeText(this, "Item 2 clicked", Toast.LENGTH_SHORT).show();
                return true;
            case R.id.item3:
                Toast.makeText(this, "Item 3 clicked", Toast.LENGTH_SHORT).show();
                return true;
            case R.id.item4:
                Toast.makeText(this, "Item 4 clicked", Toast.LENGTH_SHORT).show();
                return true;
            default:
                return false;
        }
    }
}