谷歌发布了Android的ViewPager2测试版，让我们看看它有什么不同。
Android ViewPager2
首先使用ViewPager2,先在build.gradle添加依赖
implementation 'androidx.viewpager2:viewpager2:1.0.0-alpha01'
Android ViewPager2的特性
- 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
ViewPaver2与ViewPager的区别
同样在xml中使用一样。
<androidx.viewpager2.widget.ViewPager2
android:id="@+id/viewpager2"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
在以前的ViewPager的addOnPageChangeListener方法，我们需要覆盖三个方法。回顾下代码如下
viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
@Override
public void onPageSelected(int position) {
}
@Override
public void onPageScrollStateChanged(int state) {
}
});
在ViewPager2中，不再需要这样的重写。
mviewPager2.registerOnPageChangeCallback(new ViewPager2.OnPageChangeCallback() {
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
super.onPageScrolled(position, positionOffset, positionOffsetPixels);
}
});
垂直方向属性
默认是水平方向ORIENTATION_HORIZONTAL,垂直是ORIENTATION_VERTICAL
mviewPager2.setOrientation(ViewPager2.ORIENTATION_VERTICAL);
ViewPager2与RecycleView的结合使用
接下来，我们使用RecyclerView.Adapter来结合ViewPager2一起使用。不再需要像ViewPager使用FragmentStateAdapter。
项目结构如下:
struct.png
activity_main.xml代码
<?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>
MainActivity的代码
public class MainActivity extends AppCompatActivity {
ViewPager2 mviewPager2;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mviewPager2 = findViewById(R.id.viewpager2);
List<String> list = new ArrayList<>();
list.add("页面一");
list.add("页面二");
list.add("页面三");
list.add("页面四");
mviewPager2.setAdapter(new ViewPagerAdapter(this, list, mviewPager2));
}
}
列表Item的布局recycleview_item.xml
<?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">
<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>
ViewPagerAdapter的代码如下，使用跟RecycleView的adapter完全一样
package com.chaowen.androidviewpager2;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.RelativeLayout;
import android.widget.TextView;
import java.util.List;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import androidx.viewpager2.widget.ViewPager2;
/**
* @Author: wuchaowen
* @Description:
* @Time:
**/
public class ViewPagerAdapter extends RecyclerView.Adapter<ViewPagerAdapter.ViewHolder> {
private List<String> mData;
private LayoutInflater mInflater;
private ViewPager2 viewPager2;
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 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);
}
}
}
运行效果
viewpager.gif
踩坑1 Androidx和Android support库不能共存
Manifest merger failed : Attribute application@appComponentFactory value=(android.support.v4.app.CoreComponentFactory) from [com.android.support:support-compat:28.0.0] AndroidManifest.xml:22:18-91
is also present at [androidx.core:core:1.1.0-alpha04] AndroidManifest.xml:22:18-86 value=(androidx.core.app.CoreComponentFactory).
Suggestion: add 'tools:replace="android:appComponentFactory"' to <application> element at AndroidManifest.xml:6:5-22:19 to override.
解决方案
-
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
-
选择工程右键→Refactor→Migrate to Androidx
viewpager2.png
-
选中所有需要重命名的目录，执行Do Refactor
viewpager2_1.png
-
发现已经看不到support库了，运行成功安装app。
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