Android学习笔记之RecyclerView

RecyclerView是一种更强大的滚动控件，相比ListView，他不需要使用一些技巧提高运行效率，还能实现横向滚动等优点。

• 依赖库

因为Google 2018 IO 大会推出了 Android新的扩展库 AndroidX，用于替换原来的 Android扩展库，将原来的android.*替换成androidx.*；只有包名和Maven工件名受到影响，原来的类名，方法名和字段名不会更改，详情看我的上一篇博客Android到Androidx的变迁

在Android 9及之前需要添加以下内容

implementation 'com.android.support:recyclerview-v7:24.2.1'

在Android 10 需要添加

implementation 'androidx.recyclerview:recyclerview:1.1.0'

• 基本用法

新建一个Fruit类

package com.syc.androidlearning.listViewDemo;

public class Fruit {

    private String name;
    private  int imageId;

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getImageId() {
        return imageId;
    }

    public void setImageId(int imageId) {
        this.imageId = imageId;
    }
}

修改activity_mian.xml布局文件

layout中新建fruit_item.xml

接下来需要为RecyclerView准备一个适配器，新建FruitAdapter类，继承自RecyclerView.Adapter,并将泛型指定为FruitAdapter.ViewHolder。其中，viewholder为fruitadapter中定义的一个内部类。

package com.syc.androidlearning.recyclerView;

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

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import com.syc.androidlearning.R;
import com.syc.androidlearning.listViewDemo.Fruit;

import java.util.List;

public class FruitAdapter extends RecyclerView.Adapter {

    private List mFruitList;

    static class ViewHolder extends RecyclerView.ViewHolder{
        ImageView fruitImage;
        TextView fruitName;

        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            fruitImage = itemView.findViewById(R.id.fruit_image);
            fruitName = itemView.findViewById(R.id.fruit_name);
        }
    }

    public FruitAdapter(List mFruitList) {
        this.mFruitList = mFruitList;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull 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(@NonNull ViewHolder holder, int position) {
        Fruit fruit = mFruitList.get(position);
        holder.fruitName.setText(fruit.getName());
        holder.fruitImage.setImageResource(fruit.getImageId());
    }

    @Override
    public int getItemCount() {
        return mFruitList.size();
    }



}

最后，修改MainActivity中的代码

package com.syc.androidlearning;

import androidx.appcompat.app.ActionBar;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.Toast;

import com.syc.androidlearning.listViewDemo.Fruit;
import com.syc.androidlearning.recyclerView.FruitAdapter;

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

public class MainActivity extends AppCompatActivity {

    private List fruitList = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initFruits();
        RecyclerView recyclerView = findViewById(R.id.recycler_view);
        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);
        FruitAdapter fruitAdapter = new FruitAdapter(fruitList);
        recyclerView.setAdapter(fruitAdapter);
    }

    private void initFruits() {

        for (int i = 1; i < 10; ++i) {
            Fruit apple = new Fruit("apple", R.drawable.ic_launcher_background);
            fruitList.add(apple);
        }
    }
}