Android之適配器（RecyclerView)

一、layout

1、activity_main.xml

<?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"
    >

    <!-- 由於RecyclerView不是內置在系統SDK當中的，所以需要把完整的包路徑寫出來   -->
    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</LinearLayout>

 2、fruit_item.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="wrap_content"
    android:layout_margin="5dp"
    >
    <!--
    android:orientation="vertical" 將LinearLayout設置爲垂直佈局
    android:layout_width="100dp" 將寬度設置爲100dp
     -->

    <!--
    android:layout_margin="5dp" 讓子項之間相隔5dp
       -->

    <ImageView
        android:id="@+id/fruit_image"
        android:layout_width="64dp"
        android:layout_height="62dp"
        android:layout_gravity="center_horizontal" />

    <TextView
        android:id="@+id/fruit_name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="left"
        android:layout_marginTop="10dp"/>

    <!--
        android:layout_gravity="center_horizontal" 設置水平居中
        android:layout_marginTop="10dp" 讓文字與圖片保持一些距離  -->

    <!--
        android:layout_gravity="left"
        居左對齊，等下文字的長度變長，居中會顯得很奇怪-->

</LinearLayout>



<!--爲指定的RecyclerView的子項指定我們自定義的佈局fruit_item.xml-->

二、Java代碼

1、Fruit類

package com.example.recycleviewtest;

//新建類Fruit，作爲RecyclerView適配器的適配類型
public class Fruit {

    private String name;

    private int  imageId;

    public Fruit(String name,int imageId){
        this.imageId=imageId;
        this.name=name;
    }


    public int getImageId() {
        return imageId;
    }

    public String getName() {
        return name;
    }
}

2、FruitAdapter適配器

package com.example.recycleviewtest;


import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import java.util.List;

/**
 * 創建了自定義的適配器，繼承於RecyclerView.Adapter，將泛型指定爲FruitAdapter.ViewHolder
 */
public class FruitAdapter extends RecyclerView.Adapter<FruitAdapter.ViewHolder> {


    private List<Fruit> mFruitList;

    /**
     * 定義內部類ViewHolder 繼承自 RecyclerView.ViewHolder
     */
    static class ViewHolder extends RecyclerView.ViewHolder {
        View fruitView;//子項最外層佈局實例
        ImageView fruitImage;
        TextView fruitName;

        /**
         * 構造參數中傳入參數view
         * @param view RecyclerView子項的最外層佈局
         */
        public ViewHolder(@NonNull View view) {
            super(view);
            fruitView=view;
            fruitImage=(ImageView)view.findViewById(R.id.fruit_image);
            fruitName=(TextView)view.findViewById(R.id.fruit_name);
        }
    }

    /**
     * 傳入數據源
     * 構造函數
     * @param fruitList
     */
    public FruitAdapter(List<Fruit> fruitList){
        mFruitList=fruitList;
    }

    /**
     * 重寫onCreateViewHolder方法，用於創建ViewHolder實例，並把加載出來的佈局傳入到構造函數中，最後將ViewHolder的實例返回
     * @param parent
     * @param viewType
     * @return
     */
    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view= LayoutInflater.from(parent.getContext())
                .inflate(R.layout.fruit_item,parent,false);

        //聲明爲final，這樣匿名內部類中也能獲取
        final ViewHolder holder=new ViewHolder(view);

        //重寫onClick方法，爲Fruit的視圖view設置單擊監聽器
        holder.fruitView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //獲得被單擊的item的實例
                int position=holder.getAdapterPosition();
                Fruit fruit=mFruitList.get(position);
                //提示信息
                Toast.makeText(v.getContext(),"You clicked view "+fruit.getName(),Toast.LENGTH_SHORT).show();
            }
        });

        //重寫OnClick方法，爲Fruit的圖片image也設置單擊監聽器
        holder.fruitImage.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int position=holder.getAdapterPosition();
                Fruit fruit=mFruitList.get(position);
                Toast.makeText(v.getContext(),"You cliked image "+fruit.getName(),Toast.LENGTH_SHORT).show();
            }
        });
        return holder;
    }

    /**
     * 對RecyclerView子項的數據進行賦值，會在每個子項被滾動到屏幕內的時候執行
     * @param holder
     * @param position
     */
    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        Fruit fruit=mFruitList.get(position);
        holder.fruitImage.setImageResource(fruit.getImageId());
        holder.fruitName.setText(fruit.getName());
    }

    /**
     * 告訴RecyclerView有多少子項
     * @return
     */
    @Override
    public int getItemCount() {
        return mFruitList.size();
    }


}

3、主方法MainActivity

package com.example.recycleviewtest;

import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.GridLayoutManager;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import androidx.recyclerview.widget.StaggeredGridLayoutManager;

import android.os.Bundle;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;

public class MainActivity extends AppCompatActivity {

    private List<Fruit> fruitList=new ArrayList<>();
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        //初始化水果數據
        initFruits();

        //獲取RecyclerView的實例
        RecyclerView recyclerView=(RecyclerView)findViewById(R.id.recycler_view);

        //參數1：把佈局分成三列   參數2：讓佈局縱向排列
        //指定RecyclerView的佈局方式爲 3列縱向瀑布流佈局
        StaggeredGridLayoutManager layoutManager=new StaggeredGridLayoutManager(
                3,StaggeredGridLayoutManager.VERTICAL);

//        GridLayoutManager layoutManager=new GridLayoutManager(this,5,GridLayoutManager.VERTICAL,false);

        //指定RecyclerView的佈局方式爲線性佈局
//        LinearLayoutManager layoutManager=new LinearLayoutManager(this);
        //設置佈局管理器layoutManager的佈局方向爲水平,默認爲垂直
//        layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
        
        recyclerView.setLayoutManager(layoutManager);

        //爲RecyclerView設置Adapter
        FruitAdapter adapter=new FruitAdapter(fruitList);
        recyclerView.setAdapter(adapter);
        
    }

    private void initFruits() {

        for (int i = 0; i < 3 ; i++) {


//            Fruit apple=new Fruit("Apple",R.drawable.apple_pic);
            Fruit apple=new Fruit(getRandomLengthName("Apple"),R.drawable.apple_pic);
            fruitList.add(apple);

            Fruit banana=new Fruit(getRandomLengthName("Banana"),R.drawable.banana_pic);
            fruitList.add(banana);

            Fruit orange=new Fruit(getRandomLengthName("Orange"),R.drawable.orange_pic);
            fruitList.add(orange);

            Fruit pear=new Fruit(getRandomLengthName("Pear"),R.drawable.pear_pic);
            fruitList.add(pear);

            Fruit watermelon=new Fruit(getRandomLengthName("Watermelon"),R.drawable.watermelon_pic);
            fruitList.add(watermelon);

            Fruit grape=new Fruit(getRandomLengthName("Grape"),R.drawable.grape_pic);
            fruitList.add(grape);

            Fruit pineapple=new Fruit(getRandomLengthName("Pineapple"),R.drawable.pineapple_pic);
            fruitList.add(pineapple);

            Fruit strawberry=new Fruit(getRandomLengthName("Strawberry"),R.drawable.strawberry_pic);
            fruitList.add(strawberry);



        }
    }

    private String getRandomLengthName(String name) {

        Random random=new Random();
        int length=random.nextInt(20)+1;
        StringBuilder builder=new StringBuilder();
        for (int i = 0; i < length; i++) {
            builder.append(name);
        }
        return builder.toString();
    }
}