[英]FragmentActivity with ViewPager: Crash on orientation change
我在 FragmentActivity 中使用了 ViewPager。 當方向改變時我會崩潰。
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_list);
context = this;
loadInitialData();
setActionBar();
initializeUiComponents();
}
private void initializeUiComponents() {
// Set up the ViewPager with the sections adapter.
mViewPager = (ViewPager) findViewById(R.id.pager);
}
我的數據是動態地來自數據庫,我必須調用 Sysnctask,它在 onResume() 中從數據庫中獲取數據。 這是 Asynctask 的 onPostExecute()。
protected void onPostExecute(Void result) {
mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());
mViewPager.setAdapter(mSectionsPagerAdapter);
}
mSectionsPagerAdapter.notifyDataSetChanged();
}
}
添加 FragmentAdapterCode:
public class SectionsPagerAdapter extends FragmentPagerAdapter {
public SectionsPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
// getItem is called to instantiate the fragment for the given page.
// Return a DummySectionFragment (defined as a static inner class
// below) with the page number as its lone argument.
Fragment fragment = new PayeeListSectionFragment();
Bundle args = new Bundle();
args.putInt(PayeeListSectionFragment.ARG_SECTION_NUMBER, position + 1);
fragment.setArguments(args);
return fragment;
}
@Override
public int getCount() {
return 2;
}
@Override
public CharSequence getPageTitle(int position) {
return string;
}
}
添加片段代碼:
public class PayeeListSectionFragment extends Fragment {
/**
* The fragment argument representing the section number for this fragment.
*/
public static final String ARG_SECTION_NUMBER = "section_number";
public PayeeListSectionFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = null;
\\ rootView inflated
return rootView;
}
}
使用的xml是:
<android.support.v4.view.ViewPager
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/pager"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".PayeeListActivity" >
<!--
This title strip will display the currently visible page title, as well as the page
titles for adjacent pages.
-->
<android.support.v4.view.PagerTitleStrip
android:id="@+id/pager_title_strip"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="top"
android:background="#33b5e5"
android:paddingBottom="4dp"
android:paddingTop="4dp"
android:textColor="#fff" />
</android.support.v4.view.ViewPager>
我在方向更改時遇到以下崩潰:
06-07 11:01:57.834: E/AndroidRuntime(766): FATAL EXCEPTION: main
06-07 11:01:57.834: E/AndroidRuntime(766): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.walletv2.activity/com.walletv2.activity.PayeeListActivity}: android.support.v4.app.Fragment$InstantiationException: Unable to instantiate fragment com.walletv2.activity.PayeeListActivity$PayeeListSectionFragment: make sure class name exists, is public, and has an empty constructor that is public
06-07 11:01:57.834: E/AndroidRuntime(766): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
06-07 11:01:57.834: E/AndroidRuntime(766): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
06-07 11:01:57.834: E/AndroidRuntime(766): at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3692)
06-07 11:01:57.834: E/AndroidRuntime(766): at android.app.ActivityThread.access$700(ActivityThread.java:141)
06-07 11:01:57.834: E/AndroidRuntime(766): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1240)
06-07 11:01:57.834: E/AndroidRuntime(766): at android.os.Handler.dispatchMessage(Handler.java:99)
06-07 11:01:57.834: E/AndroidRuntime(766): at android.os.Looper.loop(Looper.java:137)
06-07 11:01:57.834: E/AndroidRuntime(766): at android.app.ActivityThread.main(ActivityThread.java:5041)
06-07 11:01:57.834: E/AndroidRuntime(766): at java.lang.reflect.Method.invokeNative(Native Method)
06-07 11:01:57.834: E/AndroidRuntime(766): at java.lang.reflect.Method.invoke(Method.java:511)
06-07 11:01:57.834: E/AndroidRuntime(766): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
06-07 11:01:57.834: E/AndroidRuntime(766): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
06-07 11:01:57.834: E/AndroidRuntime(766): at dalvik.system.NativeStart.main(Native Method)
06-07 11:01:57.834: E/AndroidRuntime(766): Caused by: android.support.v4.app.Fragment$InstantiationException: Unable to instantiate fragment com.walletv2.activity.PayeeListActivity$PayeeListSectionFragment: make sure class name exists, is public, and has an empty constructor that is public
06-07 11:01:57.834: E/AndroidRuntime(766): at android.support.v4.app.Fragment.instantiate(Fragment.java:405)
06-07 11:01:57.834: E/AndroidRuntime(766): at android.support.v4.app.FragmentState.instantiate(Fragment.java:97)
06-07 11:01:57.834: E/AndroidRuntime(766): at android.support.v4.app.FragmentManagerImpl.restoreAllState(FragmentManager.java:1767)
06-07 11:01:57.834: E/AndroidRuntime(766): at android.support.v4.app.FragmentActivity.onCreate(FragmentActivity.java:208)
06-07 11:01:57.834: E/AndroidRuntime(766): at com.walletv2.activity.PayeeListActivity.onCreate(PayeeListActivity.java:78)
06-07 11:01:57.834: E/AndroidRuntime(766): at android.app.Activity.performCreate(Activity.java:5104)
06-07 11:01:57.834: E/AndroidRuntime(766): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
06-07 11:01:57.834: E/AndroidRuntime(766): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
06-07 11:01:57.834: E/AndroidRuntime(766): ... 12 more
06-07 11:01:57.834: E/AndroidRuntime(766): Caused by: java.lang.InstantiationException: can't instantiate class com.walletv2.activity.PayeeListActivity$PayeeListSectionFragment; no empty constructor
06-07 11:01:57.834: E/AndroidRuntime(766): at java.lang.Class.newInstanceImpl(Native Method)
06-07 11:01:57.834: E/AndroidRuntime(766): at java.lang.Class.newInstance(Class.java:1319)
06-07 11:01:57.834: E/AndroidRuntime(766): at android.support.v4.app.Fragment.instantiate(Fragment.java:394)
06-07 11:01:57.834: E/AndroidRuntime(766): ... 19 more
以下幾行有幾個提示:
引起:android.support.v4.app.Fragment$InstantiationException:無法實例化片段 com.walletv2.activity.PayeeListActivity$PayeeListSectionFragment:確保類名存在,是公共的,並且有一個公共的空構造函數
和:
06-07 11:01:57.834:E/AndroidRuntime(766):由:java.lang.InstantiationException:無法實例化類 com.walletv2.activity.PayeeListActivity$PayeeListSectionFragment; 沒有空的構造函數
這表明您已向PayeeListSectionFragment
內部類添加了參數化構造函數。 不幸的是,這行不通,因為 Android 依賴於使用反射調用非參數化構造函數,以便在配置更改(除其他外)時恢復片段的狀態。
如果您想為片段提供一個或多個參數,則必須將它們插入Bundle
並將其設置為參數,使用setArguments(Bundle)
。 查看文檔中的DetailsFragment
和CountingFragment
以獲取有關如何執行此操作的示例。
這個問題也可能出現在另一種情況下,對於那些不太熟悉 Java 的人來說可能不太明顯。 如果您的片段是一個嵌套類,比如一些Activity
,請確保您聲明內部類static
。 例如,在上述問題的上下文中,它應該是一個public static class PayeeListSectionFragment
(強調static
修飾符)。 這樣內部類就不會保留對外部類的引用,並且可以擁有自己的生命周期,而不依賴於外部類。 如果沒有 static 修飾符,嵌套類不能在不實例化外部類的情況下實例化,這意味着 Android 在嘗試重新實例化片段類時會遇到問題。
另一種解決方案是將內部類移動到它自己的.java
文件中。 這樣,任何外部類依賴項都會自動刪除。
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