null object reference on getView Method

Question

I know this types of error already has been answered. But i am not able figure out the cause of error. what i am trying to accomplish is to add button dynamically into fragment from a button click which is in main activity. please help me. i am new to android development,

public class MainActivity extends AppCompatActivity {

Button add;
Fragment f;
LinearLayout ll;
View v;

@Override
protected void onCreate(final Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    add = (Button) findViewById(R.id.addButton);

    add.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            f = (ButtonFragment) getFragmentManager().findFragmentById(R.id.buttonLayout);
            //if (f != null) {
                v = f.getView();
                ll = (LinearLayout) v.findViewById(R.id.buttonLayout);
                Button dummy = new Button(v.getContext());
                LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(70, 70);
                dummy.setLayoutParams(layoutParams);
                ll.addView(dummy);
            //} else {
              //  System.out.println("View is null");
            //}

        }
    });
}


}

This is the fragment class

public class ButtonFragment extends Fragment {


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_button, container, false);
    return rootView;
}
@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
   System.out.println("View created");
}
}

this are the error code

11-25 23:15:15.442 987-987/com.example.nekib.dynamiclayoutdemo E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.nekib.dynamiclayoutdemo, PID: 987 java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.app.Fragment.getView()' on a null object reference at com.example.nekib.dynamiclayoutdemo.MainActivity$1.onClick(MainActivity.java:33) at android.view.View.performClick(View.java:4780) at android.view.View$PerformClick.run(View.java:19866) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5254) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

Did you declare this fragment in XML? Cause i don't see any runtime initialization . — ADM, Nov 25 '17 at 18:10
Post you xml here .Beside that Thats a awkward way to use of fragment . — ADM, Nov 25 '17 at 18:11

score 1 · Answer 1 · answered Nov 25 '17 at 18:19

1

You are finding a fragment that is never initiated. You are just finding it and getting its view. Fragment was never created so it has null view.

By the way correct way to replace fragments is as following.

FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
Fragment fragment = new FragmentProfile();
ft.replace(R.id.main_frame_container, fragment, fragmentName.toString());
ft.commit();

Here main_frame_container is FrameLayout in Activity's layout.

Use this method to replace or adding fragments on a view.

answered Nov 25 '17 at 18:19

Khemraj Sharma

57,232
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i am not replacing any fragment. just adding button from main activity – NEKIBUR RAHMAN Nov 25 '17 at 18:20
then can you tell me how to initiate a fragment – NEKIBUR RAHMAN Nov 25 '17 at 18:22
1

I am working in android from 2 years bro, i never used any method to make a button like this. – Khemraj Sharma Nov 25 '17 at 18:22
1

Edit your post and post your requirement so that i can tell you solution – Khemraj Sharma Nov 25 '17 at 18:23
just tell me how to get the layout of fragment in main activity please – NEKIBUR RAHMAN Nov 25 '17 at 18:24
1

You can directly get layout from xml folder, why are you pointing fragment. So i want know what you have to do. So i can tell you best solution for that. – Khemraj Sharma Nov 25 '17 at 18:29
The Fragment can be added from the XML, not needed to use Fragment transactions – OneCricketeer Nov 25 '17 at 20:20

OneCricketeer · Answer 2 · 2017-11-25T18:16:52.437

-2

First R.id.buttonLayout cannot be both a Fragment ID and a LinearLayout inside the Fragment

More importantly, you need to use getSupportFragmentManager() if you're using Support Fragment classes. Look at your import android.support.v4.app.Fragment

Besides that, though, you probably shouldn't have the button in the Activity to control the Fragment layout

edited Nov 25 '17 at 18:16

answered Nov 25 '17 at 18:10

OneCricketeer

179,855
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1

Why it has -1 ? it should work... – Selvin Nov 25 '17 at 18:11
why should not i do that – NEKIBUR RAHMAN Nov 25 '17 at 18:12
it is not Support Fragment classes – NEKIBUR RAHMAN Nov 25 '17 at 18:13
1

Lol, then it will not work with AppCompatActivity – Selvin Nov 25 '17 at 18:13
1

@NEK Your Fragment is supposed to be a separate, self contained entity from the Activity. By adding views to the Fragment from the Activity is just a bad design in Android development. Besides, your code errors at `findFragmentById`, so you should try something much different until you understand how that method works – OneCricketeer Nov 25 '17 at 18:15
i know that its a bad practice. but can you tell me how to achieve such technique – NEKIBUR RAHMAN Nov 25 '17 at 18:18
First of all, did you try moving your button into the Fragment? – OneCricketeer Nov 25 '17 at 18:25

null object reference on getView Method

2 Answers2