android开发学习——day4

自己手动创建空活动，创建和加载布局，效果：界面中出现靠上对齐的button

在活动中使用Toast，效果：对点击按钮做出响应

在活动中使用menu，效果：界面中出现菜单，并且点击对应选项会有响应

Demo：

FirstActivity.java

package com.example.hs769.activitytest;
 
import android.support.v7.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 v){
                Toast.makeText(FirstActivity.this,"You clicked Button 1",
                        Toast.LENGTH_SHORT).show();
            }
        });
    }
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main,menu);
        return true;
    }
 
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch(item.getItemId()){
            case R.id.add_item:
                Toast.makeText(this,"You click Add",Toast.LENGTH_SHORT).show();
                break;
            case R.id.remove_item:
                Toast.makeText(this,"you click Remove",Toast.LENGTH_SHORT).show();
                break;
            default:
        }
        return true;
    }
}

其中重写了两个方法

first_layout.xml

<?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="Button1"
        />
 
</LinearLayout>

main.xml

<?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>

Androidmanifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.hs769.activitytest">
 
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".FirstActivity"
            android:label="This is FirstActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>
                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>
        </activity>
    </application>
 
</manifest>