FragmentPagerAdapter是PagerAdapter中的其中一種實作。它将每一個頁面表示為一個 Fragment,并且每一個Fragment都将會儲存到fragment manager當中。而且,當使用者沒可能再次回到頁面的時候,fragment manager才會将這個Fragment銷毀。
這種pager十分适用于有一些靜态fragment,例如一組tabs,的時候使用。每個頁面對應的Fragment當使用者可以通路的時候會一直存在記憶體中,但是,當這個頁面不可見的時候,view hierarchy将會被銷毀。這樣子會導緻應用程式占有太多資源。當頁面數量比較大的時候,建議使用 FragmentStatePagerAdapter。
當使用FragmentPagerAdapter的時候,ViewPager一定要使用正确的ID set。
FragmentPagerAdapter的子類隻要實作 getItem(int) 和 getCount()方法。
public class MainActivity extends ActionBarActivity {
private ViewPager viewpager;
private LinearLayout layoutDot;
public static int NUM_ITEM = 4;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.fragment_main);
initView();
}
private void initView() {
viewpager = (ViewPager) findViewById(R.id.viewpager);
layoutDot = (LinearLayout) findViewById(R.id.groupDot);
MyFragmentPagerAdapter adapter = new MyFragmentPagerAdapter(
getSupportFragmentManager());
viewpager.setAdapter(adapter);
findViewById(R.id.btnFirst).setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
viewpager.setCurrentItem(0);
}
});
findViewById(R.id.btnLast).setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
viewpager.setCurrentItem(NUM_ITEM - 1);
}
});
}
public static class MyFragmentPagerAdapter extends FragmentPagerAdapter {
public MyFragmentPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int arg0) {
return ArrayListFragment.newInstance(arg0);
//<span style="white-space:pre"> </span>或者如下
//<span style="white-space:pre"> </span>Fragment fragment;
//<span style="white-space:pre"> </span>if (arg0 == 0) {
//<span style="white-space:pre"> </span>fragment = new MainFragment();
//<span style="white-space:pre"> </span>}else if(arg0 == 1){
//<span style="white-space:pre"> </span>fragment = new MyFragment();
//<span style="white-space:pre"> </span>}else {
//<span style="white-space:pre"> </span>fragment = null;
//<span style="white-space:pre"> </span>}
//<span style="white-space:pre"> </span>return fragment;
}
@Override
public int getCount() {
return NUM_ITEM;
}
}
public static class ArrayListFragment extends ListFragment {
int mNum;
static ArrayListFragment newInstance(int num) {
ArrayListFragment f = new ArrayListFragment();
Bundle args = new Bundle();
args.putInt("num", num);
f.setArguments(args);
return f;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mNum = getArguments() != null ? getArguments().getInt("num") : 1;
}
@Override
public View 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
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
setListAdapter(new ArrayAdapter<String>(getActivity(),
android.R.layout.simple_list_item_1, new String[] {
"hello", "hello", "hello", "hello", "hello",
"hello", }));
}
@Override
public void onListItemClick(ListView l, View v, int position, long id) {
Log.i("FragmentList", "Item clicked: " + id);
}
}
}
fragment_main的布局為:
<RelativeLayout 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:orientation="vertical" >
<Button
android:id="@+id/btnFirst"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="BtnFirst"/>
<Button
android:id="@+id/btnLast"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="@+id/btnFirst"
android:text="BtnLast"/>
<android.support.v4.view.ViewPager
android:id="@+id/viewpager"
android:layout_below="@id/btnLast"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<LinearLayout
android:id="@+id/groupDot"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:gravity="center"
android:layout_marginBottom="40dip"
android:orientation="horizontal">
</LinearLayout>
</RelativeLayout>
fragment_pager_list的布局為:
<?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" />
<!--
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
-->
<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>