RecyclerView.ViewHolder、Adapter

「爱情、让人受尽委屈。」 2023-01-07 07:08 125阅读 0赞

# RecyclerView.ViewHolder、Adapter #

### //今天同事在使用BaseQuickAdapter（万能适配器）时想了解下原生adapter怎么写 ###

## RecyclerView ##

### 用户在滑动时会**收回**隐藏的listitem RecyclerView 做的就是**回收再利用**的工作 ###

在listview的基础上添加了manager（管理者）
    	LinerLayoutManager  StaggeredGridLayoutManager（瀑布流布局）  GridLayoutManager（网格布局）
    	在这些管理者中制定了一套可扩展的布局排列接口，子类只要按照接口的规范来实现，就能定制出所需的布局了

## ViewHolder ##

### view容器 ###

就是子项itemlist最外层布局

## Adapter ##

### 适配器 ###

Adapter从模型层获取数据，然后提供给RecyclerView显示，是沟通的桥梁。创建ViewHolder和将模型层的数据绑 定到ViewHolder上

### demo ###

实体类

import lombok.Data;
    
    /** * @program: TestRecycleView * @description: 实体类 * @author: tkx * @create: 2021-01-13 14:55 **/
    @Data
    public class Fruit { 
        private String name;
        private int id;
    
        public Fruit(String name, int id) { 
            this.name = name;
            this.id = id;
        }
    
    }

### Adapter ###

适配器

import android.content.Context;
    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;
    
    
    /** * @program: TestRecycleView * @description: * @author: tkx * @create: 2021-01-13 14:30 **/
    public class FruitAdater extends RecyclerView.Adapter<FruitAdater.ViewHolder> { 
    
        private List<Fruit> mFruitList;
    //先写个静态内部类Viewholder 继承于RecyclerView.ViewHolder
        static class ViewHolder extends RecyclerView.ViewHolder { 
            View fruitView;
            ImageView fruitImage;
            TextView fruitName;
    //ViewHolder的构造函数 itemview就是要传入的子项itemlist最外层布局
            public ViewHolder(@NonNull View itemView) { 
                super(itemView);
                fruitView = itemView;
                fruitImage = itemView.findViewById(R.id.image);
                fruitName = itemView.findViewById(R.id.text);
            }
        }
    //写个构造函数方便传数据
        public FruitAdater(List<Fruit> fruitList) { 
            mFruitList = fruitList;
    
        }
    
    
        @NonNull
        @Override
        public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) { 
            View view = LayoutInflater.from(parent.getContext())
                    .inflate(R.layout.fruit_item, parent, false);
            final ViewHolder holder = new ViewHolder(view);
            holder.fruitView.setOnClickListener((View v) -> { 
                int position = holder.getAdapterPosition();
                Fruit fruit = mFruitList.get(position);
                Toast.makeText(v.getContext(), "你点了view" +
                        fruit.getName(), Toast.LENGTH_SHORT).show();
            });
            holder.fruitImage.setOnClickListener((View v) -> { 
                int position = holder.getAdapterPosition();
                Fruit fruit = mFruitList.get(position);
                Toast.makeText(v.getContext(), "你点了image" +
                        fruit.getName(), Toast.LENGTH_SHORT).show();
            });
    
            return holder;
    
        }
    
        @Override
        public void onBindViewHolder(@NonNull ViewHolder holder, int position) { 
            Fruit fruit = mFruitList.get(position);
            holder.fruitImage.setImageResource(fruit.getId());
            holder.fruitName.setText(fruit.getName());
        }
    
    
        @Override
        public int getItemCount() { 
            return mFruitList.size();
        }
    }

### Activity ###

活动类

package com.example.testrecycleview;
    
    import androidx.appcompat.app.AppCompatActivity;
    
    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;
    
    /** * @author tkx */
    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);
            initFruit();
            //瀑布流布局 可通过下面切换注释切换manager更换布局
            RecyclerView recyclerView = findViewById(R.id.rv_list);
            //实例化manager 设为三列 纵向布局
            StaggeredGridLayoutManager staggeredGridLayoutManager =new StaggeredGridLayoutManager(3,StaggeredGridLayoutManager.VERTICAL);
    // LinearLayoutManager layoutManager = new LinearLayoutManager(this);
    // layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
    // recyclerView.setLayoutManager(layoutManager);
            recyclerView.setLayoutManager(staggeredGridLayoutManager);
            FruitAdater fruitAdater = new FruitAdater(fruitList);
            //给recyclerview设置适配器
            recyclerView.setAdapter(fruitAdater);
        }
    //随便来点数据
        private void initFruit() { 
             fruitList.add(new Fruit(getRandomLength("apple"), R.drawable.ic_launcher_foreground));
             fruitList.add(new Fruit(getRandomLength("asdasd"), R.drawable.ic_launcher_foreground));
             fruitList.add(new Fruit(getRandomLength("qwe"), R.drawable.ic_launcher_foreground));
             fruitList.add(new Fruit(getRandomLength("aqweqwe"), R.drawable.ic_launcher_foreground));
             fruitList.add(new Fruit(getRandomLength("aqweqw"), R.drawable.ic_launcher_foreground));
             fruitList.add(new Fruit(getRandomLength("banana"), R.drawable.ic_launcher_foreground));
             fruitList.add(new Fruit(getRandomLength("qweqwe"), R.drawable.ic_launcher_foreground));
             fruitList.add(new Fruit(getRandomLength("aqwe"), R.drawable.ic_launcher_foreground));
             fruitList.add(new Fruit(getRandomLength("appledfsdf"), R.drawable.ic_launcher_foreground));
             fruitList.add(new Fruit(getRandomLength("appledfsdf"), R.drawable.ic_launcher_foreground));
             fruitList.add(new Fruit(getRandomLength("appledfsdf"), R.drawable.ic_launcher_foreground));
             fruitList.add(new Fruit(getRandomLength("appledfsdf"), R.drawable.ic_launcher_foreground));
             fruitList.add(new Fruit(getRandomLength("appledfsdf"), R.drawable.ic_launcher_foreground));
             fruitList.add(new Fruit(getRandomLength("appledfsdf"), R.drawable.ic_launcher_foreground));
             fruitList.add(new Fruit(getRandomLength("appledfsdf"), R.drawable.ic_launcher_foreground));
             fruitList.add(new Fruit(getRandomLength("appledfsdf"), R.drawable.ic_launcher_foreground));
             fruitList.add(new Fruit(getRandomLength("appledfsdf"), R.drawable.ic_launcher_foreground));
             fruitList.add(new Fruit(getRandomLength("appledfsdf"), R.drawable.ic_launcher_foreground));
    
        }
        //数据要长短不一瀑布流才明显 随便写个重复随机数据的方法 随机的次数是1-20的随机数
        private String getRandomLength(String name){ 
            Random random = new Random();
            int length =random.nextInt(20)+1;
            StringBuilder builder =new StringBuilder();
            for (int j = 0; j <length ; j++) { 
                    builder.append(name);
            }
            return builder.toString();
        }
    
    }

### 创建ViewHolder或者与已创建的ViewHolder相关联时就要用到Adapter ###

### 在Adapter中我们通常要实现三个方法 ###

## 1.用来创建ViewHolder ##

public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType)

## 2.用来绑定数据 ##

public void onBindViewHolder(@NonNull ViewHolder holder, int position)

## 3.返回总共要显示的列表数量 ##

public int getItemCount()

## 先，调用Adapter.getItemCount()，RecyclerView会知道数组列表中包含多少个待展示的视图。然后，RecyclerView调用Adapter.onCreateViewHolder(ViewGroup, int)创建ViewHolder。 ##

## 最后，RecyclerView会传入ViewHolder及其位置，onBindViewHolder(ViewHolder, int)来绑定数据。有了够用的ViewHolder，RecyclerView就会停止调用onCreateViewHolder()方法。回收利用旧的ViewHolder来节约内存。 ##

RecyclerView.ViewHolder、Adapter

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