Android之ViewPager总结（五）——使用Fragment实现ViewPager滑动

    今天我们来看一看Google官方推荐的一种ViewPager实现方式：使用Fragment实现ViewPager。前面的篇幅中，我们

使用的是PagerAdapter,而现在我们要使用的是FragmentPagerAdapter。

    废话不多说，我们看看官方是怎么解释的。

Implementation of PagerAdapter that represents each page as a Fragment that is persistently kept in the fragment manager as long as the user can return to the page.

This version of the pager is best for use when there are a handful of typically more static fragments to be paged through, such as a set of tabs. The fragment of each page the user visits will be kept in memory, though its view hierarchy may be destroyed when not visible. This can result in using a significant amount of memory since fragment instances can hold on to an arbitrary amount of state. For larger sets of pages, consider FragmentStatePagerAdapter.

When using FragmentPagerAdapter the host ViewPager must have a valid ID set.

Subclasses only need to implement getItem(int) and getCount() to have a working adapter.

译文：（译的不好，大家可在评论中补充）

    FragmentPagerAdapter派生自PagerAdapter，它是用来呈现Fragment页面的，这些Fragment页面会一直保存在fragment manager中，以便用户可以随时取用。

    这个适配器最好用于有限个静态fragment页面的管理。尽管不可见的视图有时会被销毁，但用户所有访问过的fragment都会被保存在内存中。因此fragment实例会保存大量的各种状态，这就造成了很大的内存开销。所以如果要处理大量的页面切换，建议使用FragmentStatePagerAdapter.

    每一个使用FragmentPagerAdapter的ViewPager都要有一个有效的ID集合，有效ID的集合就是Fragment的集合,

对于FragmentPagerAdapter的派生类，只需要重写getItem(int)和getCount()就可以了。

一 适配器的实现

package com.example.testviewpage_1;import java.util.ArrayList;import java.util.List;import android.os.Bundle;import android.support.v4.app.Fragment;import android.support.v4.app.FragmentActivity;import android.support.v4.app.FragmentPagerAdapter;import android.support.v4.view.ViewPager;public class MainActivity extends FragmentActivity {//private View view1, view2, view3;private ViewPager viewPager; // 对应的viewPager//private List<View> viewList;// view数组private List<Fragment> fragments;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);viewPager = (ViewPager) findViewById(R.id.viewpager);/*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);*/No1Fragment no1 = new No1Fragment();No2Fragment no2 = new No2Fragment();No3Fragment no3 = new No3Fragment();fragments = new ArrayList<Fragment>();fragments.add(no1);fragments.add(no2);fragments.add(no3);/*PagerAdapter pagerAdapter = new PagerAdapter() {@Overridepublic boolean isViewFromObject(View arg0, Object arg1) {return arg0 == arg1;}@Overridepublic int getCount() {return viewList.size();}@Overridepublic void destroyItem(ViewGroup container, int position,Object object) {container.removeView(viewList.get(position));}@Overridepublic Object instantiateItem(ViewGroup container, int position) {container.addView(viewList.get(position));return viewList.get(position);}};*/FragmentPagerAdapter pagerAdapter = new FragmentPagerAdapter(getSupportFragmentManager()) {@Overridepublic int getCount() {return fragments.size();}@Overridepublic Fragment getItem(int arg0) {return fragments.get(arg0);}};viewPager.setAdapter(pagerAdapter);}}

二 三个Fragment

第一个Fragment及对应的布局。

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:background="#ffffff"    android:orientation="vertical" >    </LinearLayout>

package com.example.testviewpage_1;import android.os.Bundle;import android.support.v4.app.Fragment;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;public class No1Fragment extends Fragment {@Overridepublic View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {View view = inflater.inflate(R.layout.layout1, container, false);return view;}}

第二个Fragment及对应的布局。

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:background="#ffff00"    android:orientation="vertical" >    </LinearLayout>

package com.example.testviewpage_1;import android.os.Bundle;import android.support.v4.app.Fragment;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;public class No2Fragment extends Fragment {@Overridepublic View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {View view = inflater.inflate(R.layout.layout2, container, false);return view;}}

第三个Fragment及对应的布局。

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:background="#ff00ff"    android:orientation="vertical" >    </LinearLayout>

package com.example.testviewpage_1;import android.os.Bundle;import android.support.v4.app.Fragment;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;public class No3Fragment extends Fragment {@Overridepublic View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {View view = inflater.inflate(R.layout.layout3, container, false);return view;}}