Android studio的使用2

运行按钮
First activity：

package com.example.activity;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;

import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

public class FirstActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.first_layout);
        Button button1 = (Button) findViewById(R.id.Button_1);
        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Toast.makeText(FirstActivity.this,"疼",Toast.LENGTH_SHORT).show();
            }
        });
    }
    public boolean onCreateOptionsMenu(Menu menu){
        getMenuInflater().inflate(R.menu.main,menu);
        return true;

    }
    public boolean onOptionsItemSelected(MenuItem item){
        switch (item.getItemId()){
            case R.id.add_item:
                Toast.makeText(this,"添加",Toast.LENGTH_SHORT).show();
                break;
            case R.id.remove_item:
                Toast.makeText(this,"删除",Toast.LENGTH_SHORT).show();
                 break;
            default:
        }
        return true;
    }
}
layout

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
<Button
    android:id="@+id/Button_1"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Button 1"/>
</LinearLayout>