[移动开发]Recycler view初探（一）

recycler view是安卓5.0中的重大更新。在主类中重写Myviewholder和Myadpter，然后在Recycleview中绑定adpter，实现初步功能。
首先在gradle中添加依赖库：

    implementation 'androidx.recyclerview:recyclerview:1.1.0'

在主活动中添加引入：

import androidx.recyclerview.widget.RecyclerView;

在activity_main.xml中添加布局控件：

 <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerview"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

recycler view是基于相同事物的“数组”模型，不妨先建立news类文件：

package com.example.myapplication10;

public class News {
    public String title;
    public String content;
}

建立“数组”，初始化数据，实例化Recyclerview变量：

 RecyclerView mRecycleView=findViewById(R.id.recyclerview);
        for(int i=0;i<20;i++)
        {
            News news=new News();
            news.title="林允儿和你结婚第"+i+"天";
            news.content="睡觉"+i+"次";
            mNewsList.add(news);
        }

建立Recycler View中的“数组”中的每个元素的布局问题：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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:id="@+id/rootview"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="29dp"
        android:layout_marginTop="33dp"
        android:text="标题"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="4dp"
        android:layout_marginTop="18dp"
        android:text="内容"
        app:layout_constraintStart_toStartOf="@+id/textView"
        app:layout_constraintTop_toBottomOf="@+id/textView" />


</androidx.constraintlayout.widget.ConstraintLayout>

MyviewHolder重写：
对布局文件中的控件进行实例化，实际上是控制“元素”视图的逻辑代码：

 class MyviewHolder extends RecyclerView.ViewHolder
    {
        TextView textitle;
        TextView textcontent;
        ConstraintLayout mrootview;
        public MyviewHolder(@NonNull View itemView) {
            super(itemView);
            textitle=itemView.findViewById(R.id.textView);
            textcontent=itemView.findViewById(R.id.textView2);
            mrootview=itemView.findViewById(R.id.rootview);
        }
    }

其中rootview是“元素”布局文件的id：

android:id="@+id/rootview"

重写adpter,第一个函数是实例化view元素布局，生成元素视图控件，第二个函数是绑定元素视图控件到特定的位置，第三个是返回大小：

class Myadapter extends RecyclerView.Adapter<MyviewHolder>
    {

        @NonNull
        @Override
        public MyviewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
            View view=View.inflate(MainActivity.this,R.layout.item_list,null);
            MyviewHolder Myviewholder=new MyviewHolder(view);
            return Myviewholder;
        }

        @Override
        public void onBindViewHolder(@NonNull MyviewHolder holder, final int position) {
            News news=mNewsList.get( position);
            holder.textitle.setText(news.title);
            holder.textcontent.setText(news.content);
            holder.mrootview.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Toast.makeText(MainActivity.this,"你们有"+position+"个孩子",Toast.LENGTH_LONG).show();
                }
            });


        }

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

}

设置管理器，设置风格，设置分割线：

 Myadapter myadapter=new Myadapter();
        mRecycleView.setAdapter(myadapter);
        LinearLayoutManager layoutManager=new LinearLayoutManager(MainActivity.this);
        mRecycleView.setLayoutManager(layoutManager);
        DividerItemDecoration divd=new DividerItemDecoration(this,DividerItemDecoration.VERTICAL);
        mRecycleView.addItemDecoration(divd);

则完成如下app:

Main activity总代码：

package com.example.myapplication10;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.constraintlayout.widget.ConstraintLayout;
import androidx.recyclerview.widget.DividerItemDecoration;
import androidx.recyclerview.widget.RecyclerView;
import androidx.recyclerview.widget.LinearLayoutManager;


import android.os.Bundle;
import android.widget.TextView;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Toast;

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



public class MainActivity extends AppCompatActivity {
    List<News> mNewsList=new ArrayList<>();




    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //RecyclerView mRecycleView=(RecyclerView)this.findViewById(R.id.recyclerview);
        RecyclerView mRecycleView=findViewById(R.id.recyclerview);
        for(int i=0;i<20;i++)
        {
            News news=new News();
            news.title="林允儿和你结婚第"+i+"天";
            news.content="睡觉"+i+"次";
            mNewsList.add(news);
        }
        Myadapter myadapter=new Myadapter();
        mRecycleView.setAdapter(myadapter);
        LinearLayoutManager layoutManager=new LinearLayoutManager(MainActivity.this);
        mRecycleView.setLayoutManager(layoutManager);
        DividerItemDecoration divd=new DividerItemDecoration(this,DividerItemDecoration.VERTICAL);
        mRecycleView.addItemDecoration(divd);

    }


    class MyviewHolder extends RecyclerView.ViewHolder
    {
        TextView textitle;
        TextView textcontent;
        ConstraintLayout mrootview;
        public MyviewHolder(@NonNull View itemView) {
            super(itemView);
            textitle=itemView.findViewById(R.id.textView);
            textcontent=itemView.findViewById(R.id.textView2);
            mrootview=itemView.findViewById(R.id.rootview);
        }
    }
    class Myadapter extends RecyclerView.Adapter<MyviewHolder>
    {

        @NonNull
        @Override
        public MyviewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
            View view=View.inflate(MainActivity.this,R.layout.item_list,null);
            MyviewHolder Myviewholder=new MyviewHolder(view);
            return Myviewholder;
        }

        @Override
        public void onBindViewHolder(@NonNull MyviewHolder holder, final int position) {
            News news=mNewsList.get( position);
            holder.textitle.setText(news.title);
            holder.textcontent.setText(news.content);
            holder.mrootview.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Toast.makeText(MainActivity.this,"你们有"+position+"个孩子",Toast.LENGTH_LONG).show();
                }
            });


        }

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

}