Fragment与Viewpager及FragmentStatePagerAdapter

前两篇我们讲过PagerAdapter和FragmentPagerAdapter，这里将介绍第三个适配器即FragmentStatePagerAdapter，它和ListView有点类似，会保存当前界面，以及下一个界面和上一个界面(如果有)，最多会保存3个，其他会被销毁掉。需要注意的是FragmentStatePagerAdapter可能会不经意间造成内存未正常回收，严重导致内存溢出，比如图片资源没有释放，资源引用问题。

MainActivity.java代码：

public class MainActivity extends FragmentActivity {private ViewPager viewPager;static final int NUM_ITEMS = 10;// 定义一共有10页private MyAdapter adapter;private Button go_first;private Button go_last;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);viewPager = (ViewPager) this.findViewById(R.id.pager);adapter = new MyAdapter(getSupportFragmentManager());go_first = (Button) this.findViewById(R.id.goto_first);go_last = (Button) this.findViewById(R.id.goto_last);go_first.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubviewPager.setCurrentItem(0);}});go_last.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubviewPager.setCurrentItem(NUM_ITEMS - 1);}});viewPager.setAdapter(adapter);}// 填充适配器的数据:每一页都是Fragmentpublic static class MyAdapter extends FragmentStatePagerAdapter {public MyAdapter(FragmentManager fm) {super(fm);// TODO Auto-generated constructor stub}@Overridepublic Fragment getItem(int arg0) {// TODO Auto-generated method stubreturn ArrayListFragment.getIntances(arg0);}@Overridepublic int getCount() {// TODO Auto-generated method stubreturn NUM_ITEMS;}}public static class ArrayListFragment extends ListFragment {int num;static ArrayListFragment getIntances(int num) {ArrayListFragment listFragment = new ArrayListFragment();Bundle bundle = new Bundle();bundle.putInt("num", num);listFragment.setArguments(bundle);return listFragment;}@Overridepublic void onActivityCreated(Bundle savedInstanceState) {// TODO Auto-generated method stubsuper.onActivityCreated(savedInstanceState);setListAdapter(new ArrayAdapter<String>(getActivity(),android.R.layout.simple_list_item_1, getData()));}public List<String> getData() {List<String> list = new ArrayList<String>();for (int i = 0; i < 20; i++) {list.add("jack" + i);}return list;}@Overridepublic void onCreate(Bundle savedInstanceState) {// TODO Auto-generated method stubsuper.onCreate(savedInstanceState);System.out.println("------>>" + num);num = (getArguments() != null ? getArguments().getInt("num") : 1);}@Overridepublic View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {View view = inflater.inflate(R.layout.fragment_pager_list, null);TextView textView = (TextView) view.findViewById(R.id.text);textView.setText("Fragment #" + num);// TODO Auto-generated method stubreturn view;}@Overridepublic void onPause() {// TODO Auto-generated method stubsuper.onPause();}@Overridepublic void onListItemClick(ListView l, View v, int position, long id) {Log.i("FragmentList", "Item clicked: " + id);}}@Overridepublic boolean onCreateOptionsMenu(Menu menu) {// Inflate the menu; this adds items to the action bar if it is present.getMenuInflater().inflate(R.menu.main, menu);return true;}}

activity_main.xml:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:gravity="center_horizontal"    android:orientation="vertical"    android:padding="4dip"    tools:context=".MainActivity" >    <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>    <LinearLayout        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:layout_weight="0"        android:gravity="center"        android:measureWithLargestChild="true"        android:orientation="horizontal" >        <Button            android:id="@+id/goto_first"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:text="跳到首页" >        </Button>        <Button            android:id="@+id/goto_last"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:text="跳到尾页" >        </Button>    </LinearLayout></LinearLayout>

fragment_pager_list.xml:

<?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="@android:drawable/gallery_thumb"    android:orientation="vertical" >    <TextView        android:id="@+id/text"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:gravity="center_vertical|center_horizontal"        android:text="@string/hello_world"        android:textAppearance="?android:attr/textAppearanceMedium" />    <!--    The frame 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        -->        <ListView            android: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 -->        <TextView            android:id="@android:id/empty"            android:layout_width="match_parent"            android:layout_height="match_parent"            android:text="No items."            android:textAppearance="?android:attr/textAppearanceMedium" />    </FrameLayout></LinearLayout>