一、运行一个Android程序步骤
1.需要创建活动
目录:Project/app/src/main/java/com.example.activitytest/MainActivity(手动创建)
2.创建活动和加载布局
3.在AndroidManifest.xml中注册
MainActivity.java代码:
package com.example.firstactivity;
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 MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.frist_layout);//加载一个布局
Button button1 = (Button) findViewById(R.id.button_1); //获取按钮得到的实例
button1.setOnClickListener(new View.OnClickListener() { //建立监听器
@Override
public void onClick(View v) {
//makeText 有3个参数,最后调用show()
Toast.makeText(MainActivity.this, "you click button1", Toast.LENGTH_LONG).show();
}
} );
}
//getMenuInflater返回inflate对象,调用inflate就可以为当前的活动创建菜单
public boolean onCreateOptionsMenu(Menu menu){
getMenuInflater().inflate(R.menu.main, menu);
return true; //返回true 将菜单显示返回false不显示菜单
}
public boolean onOptionsItemSelected(MenuItem item){
switch (item.getItemId()){
case R.id.add_item:
Toast.makeText(this,"you click add_item",Toast.LENGTH_SHORT).show();
break;
case R.id.remove_item:
Toast.makeText(this,"you click remove_item",Toast.LENGTH_LONG).show();
break;
default:
}
return true;
}
}
Projects\FirstActivity\app\src\main\res\layout\frist_layout.xml文件代码:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
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>
Projects\FirstActivity\app\src\main\res\menu\main.xml菜单文件代码
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item
android:id="@+id/add_item"
android:title="Add" />
<item
android:id="@+id/remove_item"
android:title="Remove"/>
</menu>