FragmentPagerAdapter
FragmentPagerAdapter是PagerAdapter中的其中一种实现。它将每一个页面表示为一个 Fragment，并且每一个Fragment都将会保存到fragment manager当中。而且，当用户没可能再次回到页面的时候，fragment manager才会将这个Fragment销毁。
这种pager十分适用于有一些静态fragment，例如一组tabs，的时候使用。每个页面对应的Fragment当用户可以访问的时候会一直存在内存中，但是，当这个页面不可见的时候，view hierarchy将会被销毁。这样子会导致应用程序占有太多资源。当页面数量比较大的时候，建议使用 FragmentStatePagerAdapter。
当使用FragmentPagerAdapter的时候，ViewPager一定要使用正确的ID set。
FragmentPagerAdapter的子类只要实现 getItem(int) 和 getCount()方法。
下面是示例代码：
publicclassFragmentPagerSupportextendsFragmentActivity{
staticfinalint NUM_ITEMS =10;
MyAdapter mAdapter;
ViewPager mPager;
@Override
protectedvoid onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.fragment_pager);
mAdapter =newMyAdapter(getSupportFragmentManager());
mPager =(ViewPager)findViewById(R.id.pager);
mPager.setAdapter(mAdapter);
// Watchfor button clicks.
Button button =(Button)findViewById(R.id.goto_first);
button.setOnClickListener(newOnClickListener(){
publicvoid onClick(View v){
mPager.setCurrentItem(0);
}
});
button =(Button)findViewById(R.id.goto_last);
button.setOnClickListener(newOnClickListener(){
publicvoid onClick(View v){
mPager.setCurrentItem(NUM_ITEMS-1);
}
});
}
publicstaticclassMyAdapterextendsFragmentPagerAdapter{
publicMyAdapter(FragmentManager fm){
super(fm);
}
@Override
publicint getCount(){
return NUM_ITEMS;
}
@Override
publicFragment getItem(int position){
returnArrayListFragment.newInstance(position);
}
}
publicstaticclassArrayListFragmentextendsListFragment{
int mNum;
/**
* Create a new instance ofCountingFragment, providing "num"
* as an argument.
*/
staticArrayListFragment newInstance(int num){
ArrayListFragment f =newArrayListFragment();
// Supply num input as an argument.
Bundle args =newBundle();
args.putInt("num", num);
f.setArguments(args);
return f;
}
/**
* When creating, retrieve thisinstance's number from its arguments.
*/
@Override
publicvoid onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
mNum = getArguments()!=null? getArguments().getInt("num"):1;
}
/**
* The Fragment's UI is just a simpletext view showing its
* instance number.
*/
@Override
publicView onCreateView(LayoutInflater inflater,ViewGroup container,
Bundle savedInstanceState){
View v = inflater.inflate(R.layout.fragment_pager_list, container,false);
View tv = v.findViewById(R.id.text);
((TextView)tv).setText("Fragment #"+ mNum);
return v;
}
@Override
publicvoid onActivityCreated(Bundle savedInstanceState){
super.onActivityCreated(savedInstanceState);
setListAdapter(newArrayAdapter<String>(getActivity(),
android.R.layout.simple_list_item_1,Cheeses.sCheeseStrings));
}
@Override
publicvoid onListItemClick(ListView l,View v,int position,long id){
Log.i("FragmentList","Item clicked: "+ id);
}
}
}
The R.layout.fragment_pager resource of the top-level fragment is:
<LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"android:padding="4dip"
android:gravity="center_horizontal"
android:layout_width="match_parent"android:layout_height="match_parent">
<android.support.v4.view.ViewPager
android:id="@+id/pager"
android:layout_width="match_parent"
android:layout_height="0px"
android:layout_weight="1">
</android.support.v4.view.ViewPager>
<LinearLayoutandroid:orientation="horizontal"
android:gravity="center"android:measureWithLargestChild="true"
android:layout_width="match_parent"android:layout_height="wrap_content"
android:layout_weight="0">
<Buttonandroid:id="@+id/goto_first"
android:layout_width="wrap_content"android:layout_height="wrap_content"
android:text="@string/first">
</Button>
<Buttonandroid:id="@+id/goto_last"
android:layout_width="wrap_content"android:layout_height="wrap_content"
android:text="@string/last">
</Button>
</LinearLayout>
</LinearLayout>
The R.layout.fragment_pager_list resource containing each individualfragment's layout is:
<LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@android:drawable/gallery_thumb">
<TextViewandroid:id="@+id/text"
android:layout_width="match_parent"android:layout_height="wrap_content"
android:gravity="center_vertical|center_horizontal"
android:textAppearance="?android:attr/textAppearanceMedium"
android:text="@string/hello_world"/>
<!-- Theframe layout is here since we will be showing either
the empty view or the list view. -->
<FrameLayout
android:layout_width="match_parent"
android:layout_height="0dip"
android:layout_weight="1">
<!--Here is the list. Since we are using a ListActivity, we
have to call it"@android:id/list" so ListActivity will
find it -->
<ListViewandroid:id="@android:id/list"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:drawSelectorOnTop="false"/>
<!--Here is the view to show if the list is emtpy -->
<TextViewandroid:id="@android:id/empty"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:textAppearance="?android:attr/textAppearanceMedium"
android:text="No items."/>
</FrameLayout>
</LinearLayout>