【发布时间】：2013-01-14 14:07:32
【问题描述】：
我有一个带有 ViewPager 的 Android 应用程序，它允许在选项卡之间滑动。当我在选项卡之间滑动时，我调用新活动片段中的函数来更新该片段上的文本，它有时会抛出一个NullPointerException，但我无法在我的设备上复制它。想知道是否有人可以查看下面的代码和堆栈跟踪并可能提供帮助 - 将不胜感激。我不确定我是否遗漏了什么或没有正确执行此操作？
今天早上我的第一个想法是，也许我应该在单独的线程上运行它，以免干扰主 UI 线程，或者尝试/捕获这些函数，因为它们似乎只是有时会使应用程序崩溃？提前致谢。
查看PagerCode
public void onTabChanged(String tag) {
//TabInfo newTab = this.mapTabInfo.get(tag);
int pos = this.mTabHost.getCurrentTab();
mTabHost.getCurrentTabView().invalidate();
this.mViewPager.setCurrentItem(pos);
// calculatePoints on TabChange
if (pos == 1) {
TabFragment2 fragTrack = (TabFragment2) fragments.get(1);
fragTrack.calculatePoints();
fragTrack.createAndFillDatabase();
}
else if (pos == 2) {
TabFragment3 fragFoodList = (TabFragment3) fragments.get(2);
fragFoodList.createAndFillDatabase("none");
}
this.supportInvalidateOptionsMenu();
}
calculatePoints()
public void calculatePoints() {
int prefDailyPoints, prefPointsUsed, prefPointsRemain, prefBonusPoints, prefBonusUsed, prefBonusPointsRemain;
// Get points values and fill in respective fields
appSettings = PreferenceManager.getDefaultSharedPreferences(currentActivity);
nonDBData = currentActivity.getSharedPreferences(NONDB_DATA, 0);
prefDailyPoints = Integer.parseInt(appSettings.getString("pointsAllowed", "0"));
prefPointsUsed = nonDBData.getInt("pointsUsed", 0);
//prefPointsRemain = nonDBData.getInt("pointsRemain", prefDailyPoints - prefPointsUsed);
prefPointsRemain = prefDailyPoints - prefPointsUsed;
textfieldPointsDaily.setText(Integer.toString(prefDailyPoints));
textfieldPointsUsed.setText(Integer.toString(prefPointsUsed));
textfieldPointsRemain.setText(Integer.toString(prefPointsRemain));
if (prefPointsRemain < 0) {
textfieldPointsRemain.setTextColor(Color.rgb(255, 0, 0));
textfieldPointsRemain.setTypeface(null, Typeface.BOLD);
}
else {
textfieldPointsRemain.setTextColor(Color.rgb(0, 0, 0));
textfieldPointsRemain.setTypeface(null, Typeface.NORMAL);
}
}
堆栈跟踪
java.lang.NullPointerException
at android.preference.PreferenceManager.getDefaultSharedPreferencesName(PreferenceManager.java:371)
at android.preference.PreferenceManager.getDefaultSharedPreferences(PreferenceManager.java:366)
at com.mattdonders.android.wppcalculator.TabFragment2.calculatePoints(TabFragment2.java:667)
at com.mattdonders.android.wppcalculator.TabsViewPagerFragmentActivity.onTabChanged(TabsViewPagerFragmentActivity.java:483)
at android.widget.TabHost.invokeOnTabChangeListener(TabHost.java:446)
at android.widget.TabHost.setCurrentTab(TabHost.java:431)
at com.mattdonders.android.wppcalculator.TabsViewPagerFragmentActivity.onPageSelected(TabsViewPagerFragmentActivity.java:511)
at android.support.v4.view.ViewPager.scrollToItem(ViewPager.java:539)
at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:524)
at android.support.v4.view.ViewPager.onTouchEvent(ViewPager.java:1941)
at android.view.View.dispatchTouchEvent(View.java:7239)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2168)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1903)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2174)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1917)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2174)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1917)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2174)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1917)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2174)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1917)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2174)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1917)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2174)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1917)
at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1953)
at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1405)
at android.app.Activity.dispatchTouchEvent(Activity.java:2410)
at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1901)
at android.view.View.dispatchPointerEvent(View.java:7419)
at android.view.ViewRootImpl.deliverPointerEvent(ViewRootImpl.java:3220)
at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:3165)
at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:4292)
at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:4271)
at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:4363)
at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:179)
at android.os.MessageQueue.nativePollOnce(Native Method)
at android.os.MessageQueue.next(MessageQueue.java:125)
at android.os.Looper.loop(Looper.java:124)
at android.app.ActivityThread.main(ActivityThread.java:5039)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
at dalvik.system.NativeStart.main(Native Method)
【问题讨论】：
-
您确定 currentActivity 不为空吗？您可能在将活动附加到新片段之前调用了 calculatePoints() 方法（我不知道您调用的顺序）
-
calculatePoints()必须在该 Fragment 上调用onActivityCreated()之后才能调用。 -
我的下意识反应是怀疑你正在通过它。
-
currentActivity是在 Fragment 的 onCreateView 中定义的，Activity 总是加载 Fragment 0，所以不应该是 null 吗？这不是获取包含片段的活动的正确方法吗？currentActivity = TabFragment2.this.getActivity(); -
@dymmeh 你认为 try/catch 在这种情况下是否可行，因为我让其他人确认该应用程序在第二次打开后可以正常工作？这应该意味着它第一次尝试绑定到
currentActivity时会失败，但是在它不是 NULL 之后它应该是好的或者不是好的做法。即使在技术上应该定义currentActivity，但在我的设备上调试时，我无法将其设为 NULL。
标签： android nullpointerexception sharedpreferences