Fragment onResume() got nullpointer when using FragmentPagerAdapter

Question

I need my fragments to always call a certain function when they are the active fragment. I am using viewPager, so according this site

I create an interface class called FragmentLifecycle.java:

public interface FragmentLifecycle {

public void onResumeFragment();

}

and I Implemented this interface to my fragment:

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

and in my Activity :

       vpPager = (ViewPager) findViewById(R.id.vpg_main_content);
    adapterFragment = new PagerAdapterFragment(getSupportFragmentManager());

    vpPager.setAdapter(adapterFragment);


    vpPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
        }

        @Override
        public void onPageSelected(int newPosition) {
            Toast.makeText(ProfileActivity.this, "Selected page position: " + newPosition, Toast.LENGTH_SHORT).show();
            if (newPosition == 0) {
                FragmentLifecycle fragmentToHide = (FragmentLifecycle) adapterFragment.getItem(0);
                fragmentToHide.onResumeFragment();
            }

        }

        @Override
        public void onPageScrollStateChanged(int state) {

        }
    });
}

my fragment adapter:

    @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;
    }
}

When I run my app I got Null pointer:

                                              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)

I got error in this line Toast.makeText(getActivity(), "onResumeFragment():" + TAG, Toast.LENGTH_SHORT).show(); on my fragment.What's your idea?

@AbhishekAryan my onAttach method is : `@Override` `public void onAttach(Context context) {` `super.onAttach(context);` `profileCallBack = (ProfileCallBack) context;` `}` — sayres kabir, Feb 12 '17 at 08:30
my fragment : [ProfileFragment](http://codepad.org/Ry8cCCjx) — sayres kabir, Feb 12 '17 at 08:33

score 1 · Answer 1 · answered Feb 12 '17 at 08:33

1

try this in your Fragment:

protected Activity mActivity;

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

Now use this in Toast like:

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

answered Feb 12 '17 at 08:33

rafsanahmad007

23,683
6
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62

I have one Attach method. when I add you code I got this:`onAttach(android.app.Activity) is deprecated` – sayres kabir Feb 12 '17 at 08:41

score 0 · Accepted Answer · edited May 23 '17 at 12:24

You are getting that exception because the activity is not yet attached to the fragment when you call fragmentToHide.onResumeFragment() in your onPageSelected() callback.

Instead override setUserVisibleHint(boolean isVisibleToUser) to determine whether the fragment is visible to the user or not.

@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();
    }
}

See this question for further on this : How to determine when Fragment becomes visible in ViewPager

Fragment onResume() got nullpointer when using FragmentPagerAdapter

2 Answers2