CODEWITHSUNDEEP
androidandroid-fragmentsandroid-viewpager
Zapp Scierwx
Zapp Scierwx

Reputation: 3

Null Pointer Exception when trying to modify fragment from its Parent Activity while working with ViewPager

I'm doing an app with diffrent layout on phones and tablets. For phones I have ViewPager with Fragments and on tablets I have fragments in .xml layout file. I'm getting Null Pointer Exception when I try get particular fragment and use method from activity in that fragment.
How can I fix it? I get Null Pointer when I run app on phone with ViewPager but when I have tablet with fragments in .xml layout it is okay.

Methods in MainActivity:

  private ViewPager viewPager;
    private PagerAdapter adapter;
    private TabLayout tableLayout;

    private void setViewPager(){
            viewPager = findViewById(R.id.viewpager);
            adapter = new PagerAdapter(getSupportFragmentManager(), 2);
            adapter.addFragment(new SunFragment(), "Sun");
            adapter.addFragment(new MoonFragment(), "Moon");

            tableLayout = findViewById(R.id.tabLayout);

            if(viewPager != null) {
                viewPager.setAdapter(adapter);
            }
            if(tableLayout != null){
                tableLayout.setupWithViewPager(viewPager);
            }


        }

        private void refreshView(){
            if(viewPager != null) {
                adapter.getSunFragment().calculateWeather();
                adapter.getMoonFragment().calculateWeather();
            }else if(sunFragment != null){
                sunFragment.calculateWeather();
                moonFragment.calculateWeather();
            }

        }

Part in fragment with Null Pointer when I try use method from activity and get a double value:

 public void calculateWeather(){
        longitude = ((MainActivity)getActivity()).getLon();
        latitude = ((MainActivity)getActivity()).getLat();

    }

View Pager Adapter:

public class PagerAdapter extends FragmentStatePagerAdapter {

    private int fragmentNumber;
    private List<Fragment> fragmentList = new ArrayList<>();
    private List<String> fragmentsNameList = new ArrayList<>();


    public PagerAdapter(FragmentManager fm, int fragmentNumber){
        super(fm);
        this.fragmentNumber = fragmentNumber;
    }

    public void addFragment(Fragment fragment, String name){
        fragmentList.add(fragment);
        fragmentsNameList.add(name);
    }

    public SunFragment getSunFragment(){
        return (SunFragment)fragmentList.get(0);
    }

    public MoonFragment getMoonFragment(){
        return (MoonFragment)fragmentList.get(1);
    }
    @Override
    public Fragment getItem(int position) {
        return fragmentList.get(position);
    }

    @Override
    public int getCount() {
        return fragmentNumber;
    }

    @Override
    public CharSequence getPageTitle(int position) {
        return fragmentsNameList.get(position);
    }
}

//Edit

E/AndroidRuntime: FATAL EXCEPTION: main
                                                 Process: com.example.mariusz.astroweather, PID: 4970
                                                 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mariusz.astroweather/com.example.mariusz.astroweather.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'double com.example.mariusz.astroweather.MainActivity.getLon()' on a null object reference
                                                     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
                                                     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
                                                     at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
                                                     at android.os.Handler.dispatchMessage(Handler.java:102)
                                                     at android.os.Looper.loop(Looper.java:148)
                                                     at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                     at java.lang.reflect.Method.invoke(Native Method)
                                                     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                  Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'double com.example.mariusz.astroweather.MainActivity.getLon()' on a null object reference
                                                     at com.example.mariusz.astroweather.SunFragment.calculateWeather(SunFragment.java:56)
                                                     at com.example.mariusz.astroweather.MainActivity.refreshView(MainActivity.java:124)
                                                     at com.example.mariusz.astroweather.MainActivity.onCreate(MainActivity.java:49)
                                                     at android.app.Activity.performCreate(Activity.java:6237)
                                                     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
                                                     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
                                                     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
                                                     at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                                                     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
                                                     at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                     at android.os.Looper.loop(Looper.java:148) 
                                                     at android.app.ActivityThread.main(ActivityThread.java:5417) 
                                                     at java.lang.reflect.Method.invoke(Native Method) 
                                                     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                                                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 


com.example.mariusz.astroweather.SunFragment.calculateWeather(SunFragment.java:56)

is line :

longitude = ((MainActivity)getActivity()).getLon();

add onCreate of MainActivity:

 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        setViewPager();
        refreshView();
    }

Upvotes: 0

Views: 102

Answers (1)

Rizwan Atta
Rizwan Atta

Reputation: 3295

As per your comments if. you the fragment's powers to be used inside of the activity then you are bound to do something like this

YourFragment fragment = (YourFragment) getFragmentManager().findFragmentById(R.id.YourFragment);
//any mothed of your fragment that you like
fragment.calculateWeather();

FOR CALLING An Activity's method inside of your fragment this is the way to go

Because of your logCat I am foreseeing it that you are using your fragment to activity call method in wrong place maybe! you should use this method of yours in the fragment's OnActivityCreated() instead of using it else where?

// use this 
    public void calculateWeather(){
        longitude = ((MainActivity)getActivity()).getLon();
        latitude = ((MainActivity)getActivity()).getLat();

    }
   //as

  //in your fragment

   @Override

   public void OnActvityCreated(){
   // .... super()....
     //......
     calculateWeather();
     //......
  }

Upvotes: 0

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