5.ViewPage2使用及坑点解决

一.ViewPage2添加新特性：

  *  从右到左的布局支持
  
  *  垂直方向
  
  *  RecyclerView.Adapter取代PagerAdapter
  
  *  registerOnPageChangeCallback 取代 addPageChangeListener
  
  *  更高效的notifyDataSetChanged

二.以下案例是使用RecyclerView结合ViewPage2实现上下滑动

1.依赖导入

//ViewPage2
implementation 'androidx.viewpager2:viewpager2:1.0.0-alpha01'

//recyclerview

implementation 'androidx.recyclerview:recyclerview:1.0.0-beta01'

2.Activity和Adapter布局设置

1>.Activity布局

   <?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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

      <androidx.viewpager2.widget.ViewPager2
        android:id="@+id/viewpager2"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

    </androidx.constraintlayout.widget.ConstraintLayout>

2>.recycleview_item.xml适配器布局

  <?xml version="1.0" encoding="utf-8"?>
  <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:tools="http://schemas.android.com/tools"
     android:id="@+id/container"
     android:layout_width="match_parent"
     android:layout_height="match_parent">
     
     //原生控件
    <androidx.appcompat.widget.AppCompatTextView
       android:id="@+id/tvTitle"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:layout_centerInParent="true"
       android:textColor="@android:color/white"
       android:textSize="32sp"
       tools:text="item" />
       
   </RelativeLayout>

3.ViewPage2的适配器

package com.wd.viewpage2demo;
import android.content.Context;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.RelativeLayout;
import android.widget.TextView;
import java.util.List;

import androidx.viewpager2.widget.ViewPager2;
public class ViewPagerAdapter extends RecyclerView.Adapter<ViewPagerAdapter.ViewHolder> {

 private List<String> mData;
 private LayoutInflater mInflater;
 private ViewPager2 viewPager2;
 //定义一个色彩背景数组
private int[] colorArray = new int[]{android.R.color.black, android.R.color.holo_blue_dark, 
                                      android.R.color.holo_green_dark, android.R.color.holo_red_dark};

public ViewPagerAdapter(Context context, List<String> data, ViewPager2 viewPager2) {
    this.mInflater = LayoutInflater.from(context);
    this.mData = data;
    this.viewPager2 = viewPager2;
}

@NonNull
@Override
public ViewPagerAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    View view = mInflater.inflate(R.layout.recycleview_item, parent, false);
    return new ViewHolder(view);
}

@Override
public void onBindViewHolder(@NonNull ViewPagerAdapter.ViewHolder holder, int position) {
    String animal = mData.get(position);
    holder.myTextView.setText(animal);
    holder.relativeLayout.setBackgroundResource(colorArray[position]);

}

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

public static class ViewHolder extends RecyclerView.ViewHolder {
    TextView myTextView;
    RelativeLayout relativeLayout;

    ViewHolder(View itemView) {
        super(itemView);
        myTextView = itemView.findViewById(R.id.tvTitle);
        relativeLayout = itemView.findViewById(R.id.container);

      }
   }

}

4.Activity界面编写

package com.wd.viewpage2demo;
import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;
import java.util.ArrayList;
import java.util.List;
import androidx.viewpager2.widget.ViewPager2;

public class MainActivity extends AppCompatActivity {

private ViewPager2 viewpager2;
private List<String> list;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    //初始化控件
    initView();
    //初始化数据
    initDatas();
    //ViewPage2设置
    setViewPage2S();
}

/**
 * ViewPage2设置
 *
 * */
private void setViewPage2S() {

    /**
     * 垂直方向属性
     * 默认是水平方向ORIENTATION_HORIZONTAL,垂直是ORIENTATION_VERTICAL
     *
     * */
     //设置方向
     viewpager2.setOrientation(ViewPager2.ORIENTATION_VERTICAL);

     //设置adapter
     viewpager2.setAdapter(new ViewPagerAdapter(this, list, viewpager2));

     viewpager2.registerOnPageChangeCallback(new ViewPager2.OnPageChangeCallback() {
         @Override
         public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
             super.onPageScrolled(position, positionOffset, positionOffsetPixels);
         }

         @Override
         public void onPageSelected(int position) {
             super.onPageSelected(position);
         }

         @Override
         public void onPageScrollStateChanged(int state) {
             super.onPageScrollStateChanged(state);
         }
     });


}

/**
 * 初始化数据
 *
 * */
private void initDatas() {
    list = new ArrayList<>();
    list.add("页面一");
    list.add("页面二");
    list.add("页面三");
    list.add("页面四");

}

/**
 * 初始化控件
 *
 * */
private void initView() {
    //初始化ViewPage2
    viewpager2 = (ViewPager2) findViewById(R.id.viewpager2);
}

}

三.RecyclerView和ViewPage2结合使用出现的坑点及解决方案：

1.将build tools更新到3.2.0，gradle更新到4.6，依赖库统一更新到28.0.0，这一步非常重要，否则会导致第二步不能完全转换成功（如果已经更新过了，可以忽略这一步）

2.选择工程右键→Refactor→Migrate to Androidx：

https://img-blog.csdnimg.cn/20190311164212477.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80Mjc5NzA0OA==,size_16,color_FFFFFF,t_70

3.选中所有需要重命名的目录，执行Do Refactor：

https://img-blog.csdnimg.cn/2019031116422580.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80Mjc5NzA0OA==,size_16,color_FFFFFF,t_70