Android开发——ViewPage的使用

**（注：本篇文章的例子使用的是ConstraintLayout布局方式）
ViewPage有两种使用方式，一是直接加载布局文件（使用PagerAdapter），二是加载fragment（使用FragmentPagerAdapter）。**
效果图：

一、直接加载布局文件

1.在主布局中加入ViewPage

<?xml version="1.0" encoding="utf-8"?><android.support.constraint.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="com.example.test.MainActivity">    <android.support.v4.view.ViewPager        android:id="@+id/viewPage"        android:layout_width="0dp"        android:layout_height="0dp"        app:layout_constraintBottom_toBottomOf="parent"        app:layout_constraintLeft_toLeftOf="parent"        app:layout_constraintRight_toRightOf="parent"        app:layout_constraintTop_toTopOf="parent"></android.support.v4.view.ViewPager></android.support.constraint.ConstraintLayout>

2.新建三个layout

为了方便我们新建三个基本一样的layout。
layout1：

<?xml version="1.0" encoding="utf-8"?><android.support.constraint.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:orientation="vertical"    android:layout_width="match_parent"    android:layout_height="match_parent">    <TextView        android:layout_width="0dp"        android:layout_height="0dp"        android:text="layout1"        app:layout_constraintBottom_toBottomOf="parent"        app:layout_constraintLeft_toLeftOf="parent"        app:layout_constraintRight_toRightOf="parent"        app:layout_constraintTop_toTopOf="parent"        app:layout_constraintVertical_bias="0.498"        tools:layout_constraintBottom_creator="1"        tools:layout_constraintLeft_creator="1"        tools:layout_constraintRight_creator="1"        tools:layout_constraintTop_creator="1"        android:layout_marginLeft="0dp" /></android.support.constraint.ConstraintLayout>

layout2：

<?xml version="1.0" encoding="utf-8"?><android.support.constraint.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:orientation="vertical"    android:layout_width="match_parent"    android:layout_height="match_parent">    <TextView        android:layout_width="0dp"        android:layout_height="0dp"        android:text="layout2"        app:layout_constraintBottom_toBottomOf="parent"        app:layout_constraintLeft_toLeftOf="parent"        app:layout_constraintRight_toRightOf="parent"        app:layout_constraintTop_toTopOf="parent"        app:layout_constraintVertical_bias="0.0"        tools:layout_constraintBottom_creator="1"        tools:layout_constraintLeft_creator="1"        tools:layout_constraintRight_creator="1"        tools:layout_constraintTop_creator="1"        android:layout_marginLeft="0dp"        app:layout_constraintHorizontal_bias="0.0" /></android.support.constraint.ConstraintLayout>

layout3：

<?xml version="1.0" encoding="utf-8"?><android.support.constraint.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:orientation="vertical"    android:layout_width="match_parent"    android:layout_height="match_parent">    <TextView        android:layout_width="0dp"        android:layout_height="0dp"        android:text="layout3"        app:layout_constraintBottom_toBottomOf="parent"        app:layout_constraintLeft_toLeftOf="parent"        app:layout_constraintRight_toRightOf="parent"        app:layout_constraintTop_toTopOf="parent"        app:layout_constraintVertical_bias="0.498"        tools:layout_constraintBottom_creator="1"        tools:layout_constraintLeft_creator="1"        tools:layout_constraintRight_creator="1"        tools:layout_constraintTop_creator="1"        android:layout_marginLeft="0dp" /></android.support.constraint.ConstraintLayout>

这三个布局是添加到ViewPage中的，里面的内容非常简单，当然我们只是为了测试，你可以在其中加入更多的东西。

3.适配器PagerAdapter

新建ViewPageAdapter继承自PagerAdapter：

package com.example.test;import android.support.v4.view.PagerAdapter;import android.view.View;import android.view.ViewGroup;import java.util.List;/** * Created by Administrator on 2017/7/11. */public class ViewPageAdapter extends PagerAdapter {    private List<View> list;    public ViewPageAdapter(List<View> list) {        this.list = list;    }    /**     * @return 返回要滑动的VIew的个数     */    @Override    public int getCount() {        return list.size();    }    /**     * @param view     * @param object     * @return     */    @Override    public boolean isViewFromObject(View view, Object object) {        return view == object;    }    /**     * @param container     * @param position     * @return 做了两件事，第一：将当前视图添加到container中，第二：返回当前View     */    @Override    public Object instantiateItem(ViewGroup container, int position) {        container.addView(list.get(position));        return list.get(position);    }    /**     * @param container 从当前container中删除指定位置（position）的View     * @param position     * @param object     */    @Override    public void destroyItem(ViewGroup container, int position, Object object) {        container.removeView(list.get(position));    }}

4.在Activity中配置ViewPage

package com.example.test;import android.support.v4.view.ViewPager;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.LayoutInflater;import android.view.View;import java.util.ArrayList;import java.util.List;public class MainActivity extends AppCompatActivity {    private View view1, view2, view3;    private ViewPager viewPager;  //对应的viewPager    private List<View> viewList;//view数组    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        viewPager = (ViewPager) findViewById(R.id.viewPage);        LayoutInflater inflater=getLayoutInflater();        view1 = inflater.inflate(R.layout.layout1, null);        view2 = inflater.inflate(R.layout.layout2,null);        view3 = inflater.inflate(R.layout.layout3, null);        viewList = new ArrayList<View>();// 将要分页显示的View装入数组中        viewList.add(view1);        viewList.add(view2);        viewList.add(view3);        ViewPageAdapter adapter = new ViewPageAdapter(viewList);        viewPager.setAdapter(adapter);    }}

上面的代码将layout加载到view中，把view放到数组中并设置到Adapter中，最后给ViewPage设置Adapter。到这里第一种方式实现ViewPage就完成了。

二、加载fragment

通过加载fragment设置ViewPage与第一种方式的前两步一样，加载主布局和新建三个layout这里省略直接进行第三步。

3.新建fragment

fragment1：

package com.example.test;import android.os.Bundle;import android.support.v4.app.Fragment;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.TextView;/** * A simple {@link Fragment} subclass. */public class Fragment1 extends Fragment {    public Fragment1() {        // Required empty public constructor    }    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container,                             Bundle savedInstanceState) {        View rootView=inflater.inflate(R.layout.layout1, container, false);        return rootView;    }}

fragment2：

package com.example.test;import android.os.Bundle;import android.support.v4.app.Fragment;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;/** * A simple {@link Fragment} subclass. */public class Fragment2 extends Fragment {    public Fragment2() {        // Required empty public constructor    }    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container,                             Bundle savedInstanceState) {        View rootView=inflater.inflate(R.layout.layout2, container, false);        return rootView;    }}

fragment3：

package com.example.test;import android.os.Bundle;import android.support.v4.app.Fragment;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;/** * A simple {@link Fragment} subclass. */public class Fragment3 extends Fragment {    public Fragment3() {        // Required empty public constructor    }    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container,                             Bundle savedInstanceState) {        View rootView=inflater.inflate(R.layout.layout3, container, false);        return rootView;    }}

代码很简单，这里新建了三个fragment，分别加载三个layout。

4.适配器FragmentPagerAdapter

新建ViewPageFragmentAdapter继承自FragmentPagerAdapter：

package com.example.test;import android.support.v4.app.Fragment;import android.support.v4.app.FragmentManager;import android.support.v4.app.FragmentPagerAdapter;import java.util.ArrayList;import java.util.List;/** * Created by Administrator on 2017/7/11. */public class ViewPageFragmentAdapter extends FragmentPagerAdapter {    private List<Fragment> fragmentList = new ArrayList<>();    public ViewPageFragmentAdapter(FragmentManager fm) {        super(fm);    }    public void addFragment(Fragment fragment) {        fragmentList.add(fragment);    }    @Override    public Fragment getItem(int position) {        return fragmentList.get(position);    }    @Override    public int getCount() {        return fragmentList.size();    }}

除了必须要实现的几个方法外，这里我自定义了一个方法addFragment()，用于将fragment传递进来。

5.在Activity中配置ViewPage

package com.example.test;import android.support.v4.view.ViewPager;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.LayoutInflater;import android.view.View;import java.util.ArrayList;import java.util.List;public class MainActivity extends AppCompatActivity {    private ViewPager viewPager;  //对应的viewPager    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        viewPager = (ViewPager) findViewById(R.id.viewPage);        ViewPageFragmentAdapter adapter = new ViewPageFragmentAdapter(getSupportFragmentManager());        adapter.addFragment(new Fragment1());        adapter.addFragment(new Fragment2());        adapter.addFragment(new Fragment3());        viewPager.setAdapter(adapter);    }}

新建适配器，将fragment加入到适配器中并给ViewPage设置适配器。到这里ViewPage的第二种使用方式也讲完了。我的下一篇文章会写ViewPage与TabLayout和BottomNavigationView的组合使用，有兴趣的小伙伴可以继续阅读。