Android基础——ActionBar

<?xml version="1.0" encoding="utf-8"?>
<menu 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"
    tools:context=".MainActivity">

    <!--ActionBar中通过 app:actionViewClass 添加搜索输入框菜单选项-->
    <item android:id="@+id/search" android:title="search"
        app:actionViewClass="android.widget.SearchView"
        app:showAsAction="always" ></item>
    <!--ActionBar中添加文字菜单选项,溢出菜单选项-->
    <item android:id="@+id/bell" android:title="消 息"
        app:showAsAction="ifRoom"></item>
    <item android:id="@+id/settings" android:title="设 置"
        app:showAsAction="never" ></item>
    <!--ActionBar中的添加图片菜单选项-->
    <item android:id="@+id/about" android:title="关 于"
        app:showAsAction="always"
        app:actionLayout="@layout/rabbit_layout"></item>


</menu>

package com.example.myactionbari;

import androidx.appcompat.app.ActionBar;
import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
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.activity_main);

        //获得ActionBar对象
        final ActionBar actionBar = getSupportActionBar();

        Button button1 = (Button)findViewById(R.id.button1);
        Button button2 = (Button)findViewById(R.id.button2);
        button1.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v) {
                actionBar.hide();
            }
        });
        button2.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v) {
                actionBar.show();
            }
        });

        /*
        * 进入子活动
        * */
        Button button3 = (Button)findViewById(R.id.button3);
        button3.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(
                        MainActivity.this,StepIntoActivity.class
                );
                Toast.makeText(
                        MainActivity.this,"1",Toast.LENGTH_SHORT
                ).show();
                startActivity(intent);
            }
        });
    }

    //解析菜单资源文件
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.menu,menu);
        return super.onCreateOptionsMenu(menu);
    }
}

<activity android:name=".StepIntoActivity" android:label="朋友圈">
            <!--标记父活动-->
            <meta-data
                android:name="android.support.PARENT_ACTIVITY"
                android:value=".MainActivity"/>
        </activity>

package com.example.myactionbari;

import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.NavUtils;

import android.os.Bundle;

public class StepIntoActivity extends AppCompatActivity {

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

        //判断父Activity是否为空，不为空设置返回图标
        if(NavUtils.getParentActivityName(
                StepIntoActivity.this) != null){
            getSupportActionBar().setDisplayHomeAsUpEnabled(true);//显示向左的导航图标
        }

    }
}