RecyclerView的使用（基于Data binding）

RecyclerView自带滑动效果，可以实现横向也可纵向，这点与listview不同。默认情况是纵向的，如果需要使用横向，需要通过setLayoutManager来进行设置。

这篇文章记录了使用data binding来实现一个简单的RecyclerView的过程，其中包括两个布局文件要使用data binding，一个是包含RecyclerView的Activity的布局，另外一个是用于承载RecyclerView item的布局文件。

下面看看使用RecyclerView的关键步骤：

1. Activity布局

<?xml version="1.0" encoding="utf-8"?>
<layout 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">
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">
        <Button
            android:id="@+id/btn_trigger"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="刷新列表"/>
        <androidx.recyclerview.widget.RecyclerView
            android:id="@+id/view_recyclerview"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />
    </LinearLayout>
</layout>

2. RecyclerView 布局
   这个布局文件用于定义每条View需要显示的UI元素，这个demo显示的View从左到右要显示一个序号(TextView), 一个品牌名(TextView)

<?xml version="1.0" encoding="utf-8"?>
<layout 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">
    <data>
        <variable
            name="vm"
            type="com.mike.androidtips.recyclerViewDatabinding.DeviceModel" />
    </data>
    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="10dp"
            android:text="@{vm.rank}"
            />
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="40dp"
            android:text="@{vm.brand}"
            />
    </LinearLayout>
</layout>

3. 定义数据实体Model

package com.mike.androidtips.recyclerViewDatabinding;
import androidx.databinding.ObservableField;
public class DeviceModel {
    public ObservableField<String> rank = new ObservableField();
    public ObservableField<String> brand = new ObservableField<>();
    public DeviceModel(DataEntity dataEntity) {
        this.rank.set(dataEntity.getRank());
        this.brand.set(dataEntity.getBrand());
    }
    public void setData(DataEntity dataEntity) {
        this.rank.set(dataEntity.getRank());
        this.brand.set(dataEntity.getBrand());
    }
}

DataEntity

package com.mike.androidtips.recyclerViewDatabinding;

public class DataEntity {
    String rank;
    String brand;
    public DataEntity(String rank, String brand) {
        this.rank = rank;
        this.brand = brand;
    }
    @Override
    public String toString() {
        return "DataEntity{" +
                "rank='" + rank + '\'' +
                ", brand='" + brand + '\'' +
                '}';
    }
    public String getBrand() {
        return brand;
    }
    public String getRank() {
        return rank;
    }
}

4. 自定义一个RecyclerView的adapter，继承自RecyclerView.Adapter<RecyclerView.ViewHolder>并复写其关键方法，自定义的adapter里面需要去自定义一个ViewHolder，看下面代码:

package com.mike.androidtips.recyclerViewDatabinding;

import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

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

import com.mike.androidtips.R;
import com.mike.androidtips.databinding.RecyclerviewItemsBinding;

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

public class RecycleViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
    private final String TAG = RecycleViewAdapter.class.getSimpleName();
    List<DataEntity> dataEntities = new ArrayList<>();
    public void setDataEntities(List<DataEntity> entities) {
        dataEntities = entities;
    }

    @NonNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.recyclerview_items, parent, false);
        return new MyViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
        MyViewHolder myViewHolder = (MyViewHolder) holder;
        Log.d(TAG, "position = " + position + " , content: " + dataEntities.get(position));
        myViewHolder.binding.setVm(new DeviceModel(dataEntities.get(position)));
    }

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

    private class MyViewHolder extends RecyclerView.ViewHolder {
        public RecyclerviewItemsBinding binding;
        public MyViewHolder(@NonNull View itemView) {
            super(itemView);
            binding = RecyclerviewItemsBinding.bind(itemView);
        }
    }
}

5. Activity里面的操作步骤：
   5.1 给RecyclerView 设置setLayoutManager
   5.2 实例化一个自定义adapter对象
   5.3 给adapter赋初始list
   5.4 把adapter设置给RecyclerView

package com.mike.androidtips.recyclerViewDatabinding;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import androidx.databinding.DataBindingUtil;
import androidx.recyclerview.widget.LinearLayoutManager;
import com.mike.androidtips.R;
import com.mike.androidtips.databinding.ActivityRecyclerDatabindingBinding;
import com.mike.androidtips.databinding.ActivityTestDatabindingBinding;
import java.util.ArrayList;
import java.util.List;

public class RecyclerViewDataBindingActivity extends Activity {
    private final String TAG = RecyclerViewDataBindingActivity.class.getSimpleName();

    private RecycleViewAdapter adapter;
    ActivityRecyclerDatabindingBinding binding;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        binding = DataBindingUtil.setContentView(this, R.layout.activity_recycler_databinding);
        binding.viewRecyclerview.setLayoutManager(new LinearLayoutManager(this)); //默认是vertical
        //比如制作一个水平方向的水果列表，图标名字上下排列
        //binding.viewRecyclerview.setLayoutManager(new LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false));
        adapter = new RecycleViewAdapter();
        List<DataEntity> list = new ArrayList<>();
        DataEntity dataEntity = new DataEntity("1", "Apple");
        DataEntity dataEntity1 = new DataEntity("2", "Samsung");
        DataEntity dataEntity2 = new DataEntity("3", "OPPO");
        list.add(dataEntity);
        list.add(dataEntity1);
        list.add(dataEntity2);
        adapter.setDataEntities(list);
        binding.viewRecyclerview.setAdapter(adapter);
        initUI();
    }

    private void initUI() {
        binding.btnTrigger.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                List<DataEntity> list = new ArrayList<>();
                DataEntity dataEntity = new DataEntity("1", "Samsung");
                DataEntity dataEntity1 = new DataEntity("2", "chuanyin");
                DataEntity dataEntity2 = new DataEntity("3", "chuizi");
                DataEntity dataEntity3 = new DataEntity("4", "vivo");
                list.add(dataEntity);
                list.add(dataEntity1);
                list.add(dataEntity2);
                list.add(dataEntity3);
                adapter.setDataEntities(list);
                adapter.notifyDataSetChanged();
            }
        });
    }
}

6. 运行结果

   
   result.png

注：最初在调试时候遇到了问题：无论如何修改，整个list显示的都是最后一组数据
原因：DeviceModel里的数据被定义成了static, 干掉static即解决了问题

    public static ObservableField<String> rank = new ObservableField();
    public static ObservableField<String> brand = new ObservableField<>();