片段onResume（）在使用FragmentPagerAdapter時得到了空指針

我需要我的片段在它們是活動片段時始終調用某個函數。我使用viewPager，所以要根據this site 片段onResume（）在使用FragmentPagerAdapter時得到了空指針

我創建一個名爲FragmentLifecycle.java接口類：

public interface FragmentLifecycle { 

public void onResumeFragment(); 

}

，我實現了這個接口，以我的片段：

@Override 
public void onResumeFragment() { 
    Log.i(TAG, "onResumeFragment() running"); 
    Toast.makeText(getActivity(), "onResumeFragment():" + TAG, Toast.LENGTH_SHORT).show(); 
}

，並在我的活動：我的片段適配器：

@Override 
public Fragment getItem(int position) { 
    switch (position) { 
     case 0: // Fragment # 0 - This will show FirstFragment 
      return ProfileFragment.newInstance(0, "Profile"); 
     case 1: // Fragment # 0 - This will show FirstFragment different title 
      return EditProfileFragment.newInstance(1, "Edit"); 
     default: 
      return null; 
    } 
}

當我運行我的應用程序我得到空指針：

           java.lang.NullPointerException 
                        at android.widget.Toast.<init>(Toast.java:93) 
                        at android.widget.Toast.makeText(Toast.java:241) 
                        at com.example.sayres.myapplication7.mvp.view.profile.ProfileFragment.onResumeFragment(ProfileFragment.java:117) 
                        at com.example.sayres.myapplication7.mvp.view.profile.ProfileActivity$1.onPageSelected(ProfileActivity.java:56) 
                        at android.support.v4.view.ViewPager.dispatchOnPageSelected(ViewPager.java:1862) 
                        at android.support.v4.view.ViewPager.scrollToItem(ViewPager.java:625) 
                        at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:609) 
                        at android.support.v4.view.ViewPager.onTouchEvent(ViewPager.java:2176) 
                        at android.view.View.dispatchTouchEvent(View.java:7706) 
                        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2210) 
                        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1945) 
                        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2216) 
                        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1959) 
                        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2216) 
                        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1959) 
                        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2216) 
                        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1959) 
                        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2216) 
                        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1959) 
                        at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2068) 
                        at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1515) 
                        at android.app.Activity.dispatchTouchEvent(Activity.java:2458) 
                        at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2016) 
                        at android.view.View.dispatchPointerEvent(View.java:7886) 
                        at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:3947) 
                        at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:3826) 
                        at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3392) 
                        at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3442) 
                        at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3411) 
                        at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3518) 
                        at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3419) 
                        at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3575) 
                        at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3392) 
                        at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3442) 
                        at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3411) 
                        at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3419) 
                        at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3392) 
                        at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:5532) 
                        at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:5512) 
                        at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:5483) 
                        at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:5612) 
                        at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:185) 
                        at android.os.MessageQueue.nativePollOnce(Native Method) 
                        at android.os.MessageQueue.next(MessageQueue.java:138) 
                        at android.os.Looper.loop(Looper.java:123) 
                        at android.app.ActivityThread.main(ActivityThread.java:5001) 
                        at java.lang.reflect.Method.invokeNative(Native Method) 
                        at java.lang.reflect.Method.invoke(Method.java:515) 
                        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785) 
                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601) 
                        at dalvik.system.NativeStart.main(Native Method)

我在我的fragment.What的你的想法此行Toast.makeText(getActivity(), "onResumeFragment():" + TAG, Toast.LENGTH_SHORT).show();了錯誤？

來源

2017-02-12 sayres kabir

檢查，如果getActivity爲空！？ – rafsanahmad007

確保您的片段是先附加的。 –

然後添加調用片段onResumeFragment（）的接口 – Aryan

您獲得的例外，因爲該活動尚未連接到片段，當你調用fragmentToHide.onResumeFragment()在你的onPageSelected()回調。

改爲覆蓋setUserVisibleHint(boolean isVisibleToUser)以確定片段對用戶是否可見。

@Override 
public void setUserVisibleHint(boolean isVisibleToUser) { 
    super.setUserVisibleHint(isVisibleToUser); 
    // Your onResumeFragment() code here. 
    if (isVisibleToUser) { 
     Log.i(TAG, "onResumeFragment() running"); 
     Toast.makeText(getActivity(), "onResumeFragment():" + TAG, Toast.LENGTH_SHORT).show(); 
    } 
}

見本這個問題作進一步：How to determine when Fragment becomes visible in ViewPager

來源

2017-02-12 09:28:30

在您的片段試試這個：

protected Activity mActivity; 

@Override 
public void onAttach(Activity activity) { 
    super.onAttach(activity); 
    mActivity = activity; 
}

在Toast現在使用此類似：

if (isAdded()) { 
    Toast.makeText(mActivity, "onResumeFragment():" + TAG, Toast.LENGTH_SHORT).show(); 
}

來源

2017-02-12 08:33:01 rafsanahmad007

我有一個Attach方法。當我添加你的代碼，我得到這個：'onAttach（android.app.Activity）已棄用' –

也我得到了同樣的error.null指針 –

片段onResume（）在使用FragmentPagerAdapter時得到了空指針

回答

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