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<?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"
    android:orientation="vertical"
    >

    <TextView
        android:id="@+id/Hello"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="HelloWorld"
        android:textAlignment="center" />

</LinearLayout>

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<intent-filter>
<action android:name="android.intent.action.MAIN"/>
<category android:name="android.intent.category.LAUNCHER"/>
</intent-filter>

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public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.main_layout);
        Context context=this;//环境 上下文
        Toast.makeText(this,"Hello",Toast.LENGTH_LONG).show();

        Button button1=(Button)findViewById(R.id.Button1);
        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {//显式intent 很明显可以看到跳转逻辑
                Intent intent=new Intent(MainActivity.this,SecondActivity.class);
                startActivity(intent);
            }
        });

    }
}

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<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="h5
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center"
    >
    <Button
        android:id="@+id/Button1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Jump to Second Activity"/>

</LinearLayout>

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public class SecondActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);
        Button button2=(Button)findViewById(R.id.Button2);
        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //每个intent只能指定一个action
                Intent intent=new Intent("com.example.MainActivity.ACTION_START");
                //可以指定多个category
                intent.addCategory("android.intent.category.DEFAULT");
                startActivity(intent);
            }
        });
    }
}

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<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:gravity="center"
    tools:context=".SecondActivity">
    <Button
        android:id="@+id/Button2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Jump to first activity"
        />
</LinearLayout>

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public void onClick(View v) {//跳转到其他页面
                Intent intent=new Intent(Intent.ACTION_VIEW);
                intent.setData(Uri.parse("https://www.baidu.com"));
                startActivity(intent);
            }

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android:scheme	//用于指定数据协议部分
android:host	//指定数据主机部分
android:port	//指定数据端口
android:path	//指定主机和端口后
android:mimeType	//指定可以处理的数据类型

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public void onClick(View v) {//跳转到其他页面
                Intent intent=new Intent(Intent.ACTION_VIEW);
                intent.setData(Uri.parse("tel:10086"));
                startActivity(intent);
            }

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button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String data="HelloActivity2!";
                Intent intent=new Intent(MainActivity.this,SecondActivity.class);
                intent.putExtra("data",data);
                startActivity(intent);
            }
        });

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protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);
        TextView text=(TextView) findViewById(R.id.text);
        Intent intent=getIntent();//获取intent
        String data=intent.getStringExtra("data");
        text.setText(data);
        Log.d("MainActivityData=",data);
    }

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button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String data="HelloActivity2!";
                Intent intent=new Intent(MainActivity.this,SecondActivity.class);
                startActivityForResult(intent,1);
            }
        });

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button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent=new Intent();
                intent.putExtra("returnData","This is return data");
                setResult(RESULT_OK,intent);
                finish();
            }
        });

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protected void onActicityResult(int requestCode,int resultCode,Intent data){
        switch (requestCode){
            case 1:
                if(resultCode==RESULT_OK){
                    String returnData=data.getStringExtra("returnData");
                    Log.d("SecondActivityRetData=",returnData);

                }
                break;
            default:
        }
    }

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

    <application
        android:allowBackup="true"
        android:dataExtractionRules="@xml/data_extraction_rules"
        android:fullBackupContent="@xml/backup_rules"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.CreateActivity"
        tools:targetApi="31">
        <activity
            android:name=".DialogActivity"
            android:theme="@style/Theme.AppCompat.Dialog" />
<!-- android:theme="@android:style/Theme.Dialog" 该标签兼容性有问题-->

        <activity
            android:name=".NormalActivity"
            android:label="@string/title_activity_normal"
            android:theme="@style/Theme.CreateActivity" />
        <activity
            android:name=".MainActivity"
            android:exported="true">
<!--            exported属性标识活动是否可被外部访问,默认true,入口活动必须设置为true-->
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>
                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>

        </activity>
    </application>

</manifest>

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<?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/start_normal_activity"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Start NormalActivity"
        />
    <Button
        android:id="@+id/start_dialog_activity"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Start DialogActivity"
        />

</LinearLayout>

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<?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">
    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="This is a normal activity"/>
</LinearLayout>

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package com.example.createactivity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;


public class MainActivity extends AppCompatActivity {

    public static String tag="MainActivity";

//    @Override
//    protected void onSaveInstanceState(@NonNull Bundle outState) {
//        super.onSaveInstanceState(outState);
//        String tmpData="This is tmp data";
//        outState.putString("data_key",tmpData);
//    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.d(tag,"onCerate");
        setContentView(R.layout.activity_main);
//        if(savedInstanceState!=null){
//            String tmpData=savedInstanceState.getString("data_key");
//            Log.d(tag, "tmpdata: "+tmpData);
//        }
        Button startNormalActivity=findViewById(R.id.start_normal_activity);
        Button startDialogActivity=findViewById(R.id.start_dialog_activity);
        startNormalActivity.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent=new Intent(MainActivity.this, NormalActivity.class);
                startActivity(intent);
            }
        });
        startDialogActivity.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent=new Intent(MainActivity.this,DialogActivity.class);
                startActivity(intent);
            }
        });
    }
    @Override
    protected void onStart(){
        super.onStart();
        Log.d(tag,"onStart");
    }

    @Override
    protected void onResume() {
        super.onResume();
        Log.d(tag,"onResume");
    }

    @Override
    protected void onPause() {
        super.onPause();
        Log.d(tag, "onPause");
    }

    @Override
    protected void onStop() {
        super.onStop();
        Log.d(tag, "onStop");
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.d(tag, "onDestroy");
    }

    @Override
    protected void onRestart() {
        super.onRestart();
        Log.d(tag, "onRestart");
    }
}

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    @Override
    protected void onSaveInstanceState(@NonNull Bundle outState) {
        super.onSaveInstanceState(outState);//保存实例状态
        String tmpData="This is tmp data";
        outState.putString("data_key",tmpData);
    }

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    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.d(tag,"onCerate");
        setContentView(R.layout.activity_main);
        if(savedInstanceState!=null){//已保存实例状态不为空,有数据待获取
            String tmpData=savedInstanceState.getString("data_key");
            Log.d(tag, "tmpdata: "+tmpData);
        }
        ......
    }

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package com.example.createactivity;
import android.os.Bundle;
import android.util.Log;

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
public class BaseActivity extends AppCompatActivity {
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.d("BaseActivity",getClass().getName());
    }
}

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public static void actionStart(Context context, String data1, String data2) {
	Intent intent = new Intent(context, NormalActivity.class);
	intent.putExtra("param1", data1);
	intent.putExtra("param2", data2);
	context.startActivity(intent);
}

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        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                NormalActivity.actionStart(MainActivity.this,"data1","data2");
            }
        });

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Toast.makeText(this,"Hello",Toast.LENGTH_LONG).show();

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<?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">

    <TextView
        android:id="@+id/text_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="This is a TestView!"
        android:gravity="center"
        android:textSize="24sp"
        android:textColor="#00ff00"
        />

</LinearLayout>

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AlertDialog.Builder builder = new AlertDialog.Builder(context);//创建AlterDialog Builder用于设置
AlertDialog alertDialog = builder.create();//创建alertDialog实例
alertDialog.show();//显示

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package com.example.createactivity;

import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;

import android.app.Dialog;
import android.content.Context;
import android.content.DialogInterface;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.main_layout);
        Context context=this;//环境 上下文
        AlertDialog.Builder dialog=new AlertDialog.Builder(context);
        dialog.setPositiveButton("OK", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                //
            }
        });
        dialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                //
            }
        });
        dialog.setNeutralButton("middle", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                //
            }
        });
        dialog.setCancelable(false);//必须点击警告框按钮进行处理
        dialog.setTitle("Alert");
        dialog.setMessage("This is a Test");
        dialog.show();
    }
}

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public void MessageBox(String title,String message){
        AlertDialog.Builder dialog=new AlertDialog.Builder(this);
        dialog.setTitle(title);
        dialog.setMessage(message);

        dialog.setPositiveButton("OK", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                //
            }
        });
        dialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                //
            }
        });
        dialog.setNeutralButton("middle", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                //
            }
        });
        dialog.setCancelable(false);//必须点击警告框按钮进行处理
        dialog.show();
    }

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dependencies {
	...
    implementation libs.support.percent //新版gradle写法
    //compile 'com.android.support:percent:28.0.0' //老版本写法
    ...
}

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<?xml version="1.0" encoding="utf-8"?>
<android.support.percent.PercentFrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <Button
        android:id="@+id/button1"
        android:text="Button 1"
        android:layout_gravity="left|top"
        app:layout_widthPercent="50%"
        app:layout_heightPercent="50%"
        android:layout_height="0dp"
        android:layout_width="0dp"/>
    <Button
        android:id="@+id/button2"
        android:text="Button 2"
        android:layout_gravity="right|top"
        app:layout_widthPercent="50%"
        app:layout_heightPercent="50%"
        android:layout_height="0dp"
        android:layout_width="0dp"/>
    <Button
        android:id="@+id/button3"
        android:text="Button 3"
        android:layout_gravity="left|bottom"
        app:layout_widthPercent="50%"
        app:layout_heightPercent="50%"
        android:layout_height="0dp"
        android:layout_width="0dp"/>
    <Button
        android:id="@+id/button4"
        android:text="Button 4"
        android:layout_gravity="right|bottom"
        app:layout_widthPercent="50%"
        app:layout_heightPercent="50%"
        android:layout_height="0dp"
        android:layout_width="0dp"/>
</android.support.percent.PercentFrameLayout>

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<?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="wrap_content">

<Button
android:id="@+id/title_back"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_margin="5dp"
android:text="Back"
android:textColor="#fff"/>

<TextView
android:layout_width="0dp"
android:layout_height="wrap_content"
android:id="@+id/title_text"
android:layout_gravity="center"
android:layout_weight="1"
android:gravity="center"
android:text="Title Text"
android:textColor="#f16"
android:textSize="24sp"/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/title_edit"
android:layout_gravity="center"
android:layout_margin="5dp"
android:text="Edit"
android:textColor="#fff"/>

</LinearLayout>

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package com.example.chapter3_uiwidgettest;

import android.app.Activity;
import android.util.AttributeSet;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;
import android.content.Context;
import android.widget.Toast;

public class TitleLayout extends LinearLayout {
    public TitleLayout(Context context, AttributeSet attrs){
        super(context,attrs);//LinearLayout构造函数
        LayoutInflater.from(context).inflate(R.layout.title,this);//动态加载title布局
        //给按钮添加事件
        Button titleBack=(Button)findViewById(R.id.title_back);
        Button titleEdit=(Button)findViewById(R.id.title_edit);
        titleBack.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View view) {
                ((Activity)getContext()).finish();//销毁活动
            }
        });
        titleEdit.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View view) {
                Toast.makeText(getContext(),"You clicked Edit Button!",Toast.LENGTH_SHORT).show();
            }
        });
    }
}

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<?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"
    >
    <com.example.chapter3_uiwidgettest.TitleLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        />
</LinearLayout>

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<?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">

    <ListView
        android:id="@+id/list_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
</LinearLayout>

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public class MainActivity extends AppCompatActivity {
    private ActivityMainBinding mainBinding;
    private String[] data={"Apple","Banana","Orange","Watermelon","Pear","Grape","Pineapple",
            "Strawberry","Cherry","Mango","Apple","Banana","Orange","Watermelon","Pear","Grape","Pineapple",
            "Strawberry","Cherry","Mango"
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mainBinding=ActivityMainBinding.inflate(getLayoutInflater());
        setContentView(mainBinding.getRoot());

        ArrayAdapter<String> adapter=new ArrayAdapter<String>(MainActivity.this,android.R.layout.simple_list_item_1,data);
        ListView listView=mainBinding.listView;
        listView.setAdapter(adapter);

    }
}

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public class Fruit{
    private String name;
    private int imageId;
    public Fruit(String name,int id){
        this.name=name;
        this.imageId=id;
    }
    public String getName(){
        return name;
    }
    public int getImageId(){
        return imageId;
    }
}

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<?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="wrap_content">
    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id ="@+id/fruit_image"/>
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical"
        android:id="@+id/fruit_name"
        android:layout_marginLeft="10dp"/>
</LinearLayout>

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import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;

import org.w3c.dom.Text;

import java.util.List;

public class FruitAdapter extends ArrayAdapter<Fruit> {
    private int resourceId;//保存传入的子项布局id，用于后续动态加载

    public FruitAdapter(Context context, int textviewResourceId, List<Fruit> objects) {
        super(context, textviewResourceId, objects);
        resourceId = textviewResourceId;
    }
    //重写父类ArrayAdapter的getView
    public View getView(int position, View converView, ViewGroup parent) {
        //每个子项被滚动到屏幕内会被调用
        Fruit fruit = getItem(position);//获取当前项的Fruit实例
        View view= LayoutInflater.from(getContext()).inflate(resourceId,parent,false);// 为子项加载我们传入的布局
        ImageView fruitImage=(ImageView) view.findViewById(R.id.fruit_image);//获取实例
        TextView fruitname=(TextView) view.findViewById(R.id.fruit_name);
        fruitImage.setImageResource(fruit.getImageId());//为实例设置参数
        fruitname.setText(fruit.getName());
        return view;
    }
}

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package com.example.chapter3_uiwidgettest;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListView;

import java.util.ArrayList;
import java.util.List;


public class MainActivity extends AppCompatActivity {
    private List<Fruit> fruitList =new ArrayList<>();
    private void initFruits(){
        for (int i=0;i<2;i++){
            Fruit apple =new Fruit("Apple",R.drawable.apple_pic);
            fruitList.add(apple);
            Fruit banana = new Fruit("Banana",R.drawable.banana_pic);
            fruitList.add(banana);
            Fruit orange = new Fruit("Orange",R.drawable.orange_pic);
            fruitList.add(orange);
            Fruit watermelon = new Fruit("Watermelon",R.drawable.watermelon_pic);
            fruitList.add(watermelon);
            Fruit pear = new Fruit("Pear",R.drawable.pear_pic);
            fruitList.add(pear);
            Fruit grape = new Fruit("Grape",R.drawable.grape_pic);
            fruitList.add(grape);
            Fruit pineapple = new Fruit("Pineapple",R.drawable.pineapple_pic);
            fruitList.add(pineapple);
            Fruit strawberry = new Fruit("Strawberry",R.drawable.strawberry_pic);
            fruitList.add(strawberry);
            Fruit cherry = new Fruit("Cherry",R.drawable.cherry_pic);
            fruitList.add(cherry);
            Fruit mango = new Fruit("Mango",R.drawable.mango_pic);
            fruitList.add(mango);
        }
    }
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initFruits();
        FruitAdapter adapter=new FruitAdapter(MainActivity.this,R.layout.fruit_item,fruitList);
        ListView listView =(ListView) findViewById(R.id.list_view);
        listView.setAdapter(adapter);
    }

}

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implementation 'androidx.recyclerview:recyclerview:1.2.1'

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<?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">
    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
</LinearLayout>

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package com.example.chapter3_uiwidgettest;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import androidx.recyclerview.widget.RecyclerView;

import java.util.List;

public class FruitAdapter extends RecyclerView.Adapter<FruitAdapter.ViewHolder>{
    private List<Fruit> mFruitList;
    //继承并自定义类
    static class ViewHolder extends RecyclerView.ViewHolder{
        ImageView fruitImage;
        TextView fruitName;
        public ViewHolder(View view){
            super(view);
            fruitImage =(ImageView) view.findViewById(R.id.fruit_image);//加载图片文字实例
            fruitName =(TextView) view.findViewById(R.id.fruit_name);
        }
    }

    public FruitAdapter(List<Fruit> fruitList){
        mFruitList=fruitList;
    }
    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType){
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fruit_item,parent,false);
        ViewHolder holder=new ViewHolder(view);
        return holder;
    }
    @Override
    public void onBindViewHolder(ViewHolder holder,int position){
        Fruit fruit=mFruitList.get(position);
        holder.fruitImage.setImageResource(fruit.getImageId());
        holder.fruitName.setText(fruit.getName());
    }
    @Override
    public int getItemCount(){
        return mFruitList.size();
    }
}

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