在 ViewPager 中保存 Fragment 状态 [英] Saving Fragment state in ViewPager
问题描述
我尝试了 来自 API 的示例代码,但它并没有真正起作用,所以我实现了自己的:
FragmentPagerSupport
public class FragmentPagerSupport extends FragmentActivity {静态最终 int NUM_ITEMS = 10;MyAdapter mAdapter;ViewPager mPager;@覆盖protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);mAdapter = new MyAdapter(getSupportFragmentManager());Log.i("Pager", "mAdapter = " + mAdapter.toString());mPager = (ViewPager)findViewById(R.id.pager);如果(mPager == null)Log.i("Pager", "mPager = null");别的Log.i("Pager", "mPager = " + mPager.toString());Log.i("寻呼机", "设置寻呼机适配器");mPager.setAdapter(mAdapter);}公共静态类 MyAdapter 扩展 FragmentPagerAdapter {公共 MyAdapter(FragmentManager fm) {超级(调频);Log.i("Pager", "MyAdapter 构造函数");}@覆盖公共 int getCount() {Log.i("Pager", "MyAdapter.getCount()");返回 NUM_ITEMS;}@覆盖公共片段 getItem(int position) {Log.i("Pager", "MyAdapter.getItem()");返回 TestFragment.newInstance(position);}}公共静态类 TestFragment 扩展 Fragment {公共静态 TestFragment newInstance(int position) {Log.i("Pager", "TestFragment.newInstance()");TestFragment 片段 = 新的 TestFragment();Bundle args = new Bundle();args.putInt("位置", 位置);fragment.setArguments(args);返回片段;}@覆盖公共视图 onCreateView(LayoutInflater inflater, ViewGroup 容器,捆绑savedInstanceState) {//TODO 自动生成的方法存根Log.i("Pager", "TestFragment.onCreateView()");LinearLayout layout = (LinearLayout)inflater.inflate(R.layout.fragment_item, null);int position = getArguments().getInt("position");TextView tv = (TextView)layout.findViewById(R.id.text);tv.setText("片段#" + 位置);tv.setTextColor(Color.WHITE);tv.setTextSize(30);返回布局;}}
}
main.xml
fragment_item.xml
我的问题是,不是每次用户左右滑动时都创建一个新的 Fragment
实例,我该如何保存片段的状态(到某些数据结构)然后恢复它?>
API 演示 似乎根本没有任何状态信息保存代码.
在FragmentActivity
ViewPager.setOffscreenPageLimit()
ViewPager pager = (ViewPager) findViewById(R.id.viewPager);pager.setOffscreenPageLimit(2);
在如何查看更多信息我应该告诉我的自定义 FragmentPagerAdapter 停止销毁我的片段吗?
I tried out the sample code from the API and it didn't really work so I implemented my own:
FragmentPagerSupport
public class FragmentPagerSupport extends FragmentActivity {
static final int NUM_ITEMS = 10;
MyAdapter mAdapter;
ViewPager mPager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mAdapter = new MyAdapter(getSupportFragmentManager());
Log.i("Pager", "mAdapter = " + mAdapter.toString());
mPager = (ViewPager)findViewById(R.id.pager);
if (mPager == null)
Log.i("Pager", "mPager = null");
else
Log.i("Pager", "mPager = " + mPager.toString());
Log.i("Pager", "Setting Pager Adapter");
mPager.setAdapter(mAdapter);
}
public static class MyAdapter extends FragmentPagerAdapter {
public MyAdapter(FragmentManager fm) {
super(fm);
Log.i("Pager", "MyAdapter constructor");
}
@Override
public int getCount() {
Log.i("Pager", "MyAdapter.getCount()");
return NUM_ITEMS;
}
@Override
public Fragment getItem(int position) {
Log.i("Pager", "MyAdapter.getItem()");
return TestFragment.newInstance(position);
}
}
public static class TestFragment extends Fragment {
public static TestFragment newInstance(int position) {
Log.i("Pager", "TestFragment.newInstance()");
TestFragment fragment = new TestFragment();
Bundle args = new Bundle();
args.putInt("position", position);
fragment.setArguments(args);
return fragment;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// TODO Auto-generated method stub
Log.i("Pager", "TestFragment.onCreateView()");
LinearLayout layout = (LinearLayout)inflater.inflate(R.layout.fragment_item, null);
int position = getArguments().getInt("position");
TextView tv = (TextView)layout.findViewById(R.id.text);
tv.setText("Fragment # " + position);
tv.setTextColor(Color.WHITE);
tv.setTextSize(30);
return layout;
}
}
}
main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<android.support.v4.view.ViewPager
android:id="@+id/pager"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>
</LinearLayout>
fragment_item.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<TextView
android:id="@+id/text"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:text="@string/hello"
/>
</LinearLayout>
My question is, instead of creating a new Fragment
instance each time the user swipes left and right, how do I save a fragment's state (to some data structure) and then restore it?
The API demo doesn't seem to have any state information saving code at all.
Use ViewPager.setOffscreenPageLimit()
in FragmentActivity
ViewPager pager = (ViewPager) findViewById(R.id.viewPager);
pager.setOffscreenPageLimit(2);
See more at How do I tell my custom FragmentPagerAdapter to stop destroying my fragments?
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