Java 片段中的getActivity()返回null。父活动中的FragmentPagerAdapter存在问题?
我有一个活动,它承载一个带有两个片段的viewPager。我遇到了一个问题,在我的片段中对getActivity()的调用在活动被销毁然后重新创建后返回null(我正在更改系统设置,而我的应用程序在后台暂停,这会导致活动被销毁然后重新创建)。下面是我的家长活动的样子Java 片段中的getActivity()返回null。父活动中的FragmentPagerAdapter存在问题?,java,android,android-fragments,Java,Android,Android Fragments,我有一个活动,它承载一个带有两个片段的viewPager。我遇到了一个问题,在我的片段中对getActivity()的调用在活动被销毁然后重新创建后返回null(我正在更改系统设置,而我的应用程序在后台暂停,这会导致活动被销毁然后重新创建)。下面是我的家长活动的样子 public class MainActivity extends AppCompatActivity { private CalculatorPagerAdapter mSectionsPagerAdapter; /** *
public class MainActivity extends AppCompatActivity {
private CalculatorPagerAdapter mSectionsPagerAdapter;
/**
* The {@link ViewPager} that will host the section contents.
*/
private ViewPager mViewPager;
private final int HISTORY_PAGE_INDEX = 1;
private final int CALCULATOR_PAGE_INDEX = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
mSectionsPagerAdapter = new CalculatorPagerAdapter(getSupportFragmentManager());
// Set up the ViewPager with the sections adapter.
mViewPager = (ViewPager) findViewById(R.id.container);
mViewPager.setAdapter(mSectionsPagerAdapter);
mViewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
/**
* Refreshes the listView in the history fragment whenever the user moves to it.
* @param position
*/
@Override
public void onPageSelected(int position) {
CalculatorPagerAdapter fragmentPagerAdapter = (CalculatorPagerAdapter) mViewPager.getAdapter();
if(position == HISTORY_PAGE_INDEX){
((HistoryFragment) fragmentPagerAdapter.getItem(HISTORY_PAGE_INDEX)).refreshHistory();
}else if(position == CALCULATOR_PAGE_INDEX){
//((CalculatorFragment) fragmentPagerAdapter.getItem(CALCULATOR_PAGE_INDEX)).refreshCalculator();
}
}
@Override
public void onPageScrollStateChanged(int state) {
}
});
TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
tabLayout.setupWithViewPager(mViewPager);
}
@Override
public void onDestroy(){
super.onDestroy();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
Intent intent = new Intent(this, SettingsActivity.class);
startActivity(intent);
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A {@link FragmentPagerAdapter} that returns a fragment corresponding to
* one of the sections/tabs/pages.
*/
public class CalculatorPagerAdapter extends FragmentPagerAdapter {
HistoryFragment historyFragment;
CalculatorFragment calculatorFragment;
public CalculatorPagerAdapter(FragmentManager fm) {
super(fm);
historyFragment = new HistoryFragment();
calculatorFragment = new CalculatorFragment();
}
@Override
public Fragment getItem(int position) {
if (position ==0) return calculatorFragment;
else return historyFragment;
}
@Override
public int getCount() {
return 2;
}
@Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return "Calculator";
case 1:
return "History";
}
return null;
}
}
}
我注意到活动和片段的生命周期调用按以下顺序进行
初始创建时(正常)
11-26 12:56:21.739 31769-31769/com.example.keegan.securetipping I/Timeline: Timeline: Activity_idle id: android.os.BinderProxy@d035425 time:1218086194
11-26 12:56:24.864 31769-31769/com.example.keegan.securetipping E/InputEventReceiver: Exception dispatching input event.
11-26 12:56:24.864 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: Exception in MessageQueue callback: handleReceiveCallback
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.support.v4.app.FragmentActivity.getApplicationContext()' on a null object reference
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at com.example.keegan.securetipping.HistoryFragment.refreshHistory(HistoryFragment.java:88)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at com.example.keegan.securetipping.MainActivity$1.onPageSelected(MainActivity.java:54)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.support.v4.view.ViewPager.dispatchOnPageSelected(ViewPager.java:1794)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.support.v4.view.ViewPager.scrollToItem(ViewPager.java:569)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:553)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.support.v4.view.ViewPager.onTouchEvent(ViewPager.java:2102)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.View.dispatchTouchEvent(View.java:8547)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2400)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2093)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2372)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1722)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.app.Activity.dispatchTouchEvent(Activity.java:2742)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.support.v7.internal.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:60)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.support.v7.internal.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:60)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2333)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.View.dispatchPointerEvent(View.java:8742)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4136)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4002)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3557)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3610)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3576)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3693)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3584)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3750)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3557)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3610)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3576)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3584)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3557)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:5823)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:5797)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:5768)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:5913)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:185)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.os.MessageQueue.nativePollOnce(Native Method)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.os.MessageQueue.next(MessageQueue.java:143)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.os.Looper.loop(Looper.java:195)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at android.app.ActivityThread.main(ActivityThread.java:5373)
11-26 12:56:24.868 31769-31769/com.example.keegan.securetipping E/MessageQueue-JNI: at java.lang.reflect.Method.invoke(Native Method)
11-26 12:56:24.869 31769-31769/com.example.keegan.securetipping D/AndroidRuntime: Shutting down VM
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: FATAL EXCEPTION: main
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: Process: com.example.keegan.securetipping, PID: 31769
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.support.v4.app.FragmentActivity.getApplicationContext()' on a null object reference
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at com.example.keegan.securetipping.HistoryFragment.refreshHistory(HistoryFragment.java:88)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at com.example.keegan.securetipping.MainActivity$1.onPageSelected(MainActivity.java:54)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.support.v4.view.ViewPager.dispatchOnPageSelected(ViewPager.java:1794)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.support.v4.view.ViewPager.scrollToItem(ViewPager.java:569)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:553)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.support.v4.view.ViewPager.onTouchEvent(ViewPager.java:2102)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.View.dispatchTouchEvent(View.java:8547)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2400)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2093)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2372)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1722)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.app.Activity.dispatchTouchEvent(Activity.java:2742)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.support.v7.internal.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:60)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.support.v7.internal.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:60)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2333)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.View.dispatchPointerEvent(View.java:8742)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4136)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4002)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3557)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3610)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3576)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3693)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3584)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3750)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3557)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3610)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3576)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3584)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3557)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:5823)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:5797)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:5768)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:5913)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:185)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.os.MessageQueue.nativePollOnce(Native Method)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.os.MessageQueue.next(MessageQueue.java:143)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.os.Looper.loop(Looper.java:195)
11-26 12:56:24.874 31769-31769/com.example.keegan.securetipping E/AndroidRuntime: at android.app.ActivityThread.main(Act
这是来自引发异常的HistoryFragment类的代码位。我只是调用getApplicationContext以获取此示例的错误。通常,该错误会在我的FetchHistoryEntries异步任务中抛出
/**
* Refreshes the listView in the history fragment with data from the history database.
*/
public void refreshHistory(){
getActivity().getApplicationContext();
new FetchHistoryEntries(getActivity()).execute();
}
我的历史片段只包含一个列表视图。这是它的XML
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
>
<ListView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/history_listview"/>
当活动被销毁时,您将丢失正在使用的上下文,这就是应用程序引发异常的原因,因为您在销毁引发空指针异常的活动后调用了
getActivity()
,为避免此情况,您应将刷新历史记录更改为以下内容:
public void refreshHistory(){
if (isAdded()) {
getActivity().getApplicationContext();
new FetchHistoryEntries(getActivity()).execute();
}
}
isAdded()
当片段附加到活动且活动不为null时,返回true
你也应该考虑在你的活动被破坏时取消你的异步任务,你可以这样做:首先定义一个与你的异步任务相同类型的全局变量,比如这个代码>代码>第二,像这样执行全局任务
task = new FetchHistoryEntries(getActivity()).execute;
最后,在onDestroy重写方法中,按如下方式取消任务:
if (task != null) {
task.cancel(true);
}
希望这对你有帮助,祝你好运我实际上通过切换到FragmentStatePagerAdapter而不仅仅是FragmentPagerAdapter解决了这个问题。状态寻呼机适配器使保存和恢复碎片状态变得更容易,这正是我的问题所在。这个要点有一个很好的例子 请在第88行的历史片段中发布您的日志,说明NPE。请也发布历史片段和布局。添加相关信息。谢谢也请发布您的信息不足以发现问题,使用这段代码很难预测编译器的流程;删除此行后重试可能您的意思是(任务=新的FetchHistoryEntries(getActivity())。执行()代码>?我可以避免崩溃,但问题是如果getActivity()为null,则我无法执行需要执行的操作以使片段函数达到预期效果。从fragmentPagerAdapter返回的片段没有附加到父活动,我不知道为什么。