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;
@Override
protected 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() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
viewPager.setCurrentItem(0);
}
});
go_last.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
viewPager.setCurrentItem(NUM_ITEMS - 1);
}
});
viewPager.setAdapter(adapter);
}
// 填充适配器的数据:每一页都是Fragment
public static class MyAdapter extends FragmentStatePagerAdapter {
public MyAdapter(FragmentManager fm) {
super(fm);
// TODO Auto-generated constructor stub
}
@Override
public Fragment getItem(int arg0) {
// TODO Auto-generated method stub
return ArrayListFragment.getIntances(arg0);
}
@Override
public int getCount() {
// TODO Auto-generated method stub
return 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;
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.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;
}
@Override
public void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
System.out.println("------>>" + num);
num = (getArguments() != null ? getArguments().getInt("num") : 1);
}
@Override
public 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 stub
return view;
}
@Override
public void onPause() {
// TODO Auto-generated method stub
super.onPause();
}
@Override
public void onListItemClick(ListView l, View v, int position, long id) {
Log.i("FragmentList", "Item clicked: " + id);
}
}
@Override
public 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>