Android NullPointerException. Why?

Question

I'am new in android programming, and i have next problem: In my fragment class i need to do some action when user has clicked on button. Here is my code, he is very simple:

public class InboxFragment extends Fragment{
    private ListView ll;
    @Override

    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        return inflater.inflate(R.layout.inbox_fragment, container, false);
    }

    public void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        Button filter_bt;
        filter_bt = (Button) getView().findViewById(R.id.filter_button);
        filter_bt.setOnClickListener((OnClickListener) this);
    }
}

And here is my code of layout file:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <Button
        android:id="@+id/filter_button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/red"
        android:text="Filter by date"
        android:textColor="@color/white" />

</LinearLayout>

Here is my logs:

FATAL EXCEPTION: main
java.lang.NullPointerException
    at com.example.android.navigationdrawerexample.InboxFragment.onCreate(InboxFragment.java:29)
    at android.app.Fragment.performCreate(Fragment.java:1673)
    at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:872)
    at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1075)
    at android.app.BackStackRecord.run(BackStackRecord.java:682)
    at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1455)
    at android.app.FragmentManagerImpl$1.run(FragmentManager.java:441)
    at android.os.Handler.handleCallback(Handler.java:725)
    at android.os.Handler.dispatchMessage(Handler.java:92)
    at android.os.Looper.loop(Looper.java:137)
    at android.app.ActivityThread.main(ActivityThread.java:5306)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:511)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
    at dalvik.system.NativeStart.main(Native Method)

LOGS (2)

04-22 17:00:14.760: E/AndroidRuntime(17308): FATAL EXCEPTION: main
04-22 17:00:14.760: E/AndroidRuntime(17308): java.lang.ClassCastException: com.example.android.navigationdrawerexample.InboxFragment cannot be cast to android.view.View$OnClickListener
04-22 17:00:14.760: E/AndroidRuntime(17308):    at com.example.android.navigationdrawerexample.InboxFragment.onViewCreated(InboxFragment.java:35)
04-22 17:00:14.760: E/AndroidRuntime(17308):    at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:917)
04-22 17:00:14.760: E/AndroidRuntime(17308):    at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1075)
04-22 17:00:14.760: E/AndroidRuntime(17308):    at android.app.BackStackRecord.run(BackStackRecord.java:682)
04-22 17:00:14.760: E/AndroidRuntime(17308):    at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1455)
04-22 17:00:14.760: E/AndroidRuntime(17308):    at android.app.FragmentManagerImpl$1.run(FragmentManager.java:441)
04-22 17:00:14.760: E/AndroidRuntime(17308):    at android.os.Handler.handleCallback(Handler.java:725)
04-22 17:00:14.760: E/AndroidRuntime(17308):    at android.os.Handler.dispatchMessage(Handler.java:92)
04-22 17:00:14.760: E/AndroidRuntime(17308):    at android.os.Looper.loop(Looper.java:137)
04-22 17:00:14.760: E/AndroidRuntime(17308):    at android.app.ActivityThread.main(ActivityThread.java:5306)
04-22 17:00:14.760: E/AndroidRuntime(17308):    at java.lang.reflect.Method.invokeNative(Native Method)
04-22 17:00:14.760: E/AndroidRuntime(17308):    at java.lang.reflect.Method.invoke(Method.java:511)
04-22 17:00:14.760: E/AndroidRuntime(17308):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)
04-22 17:00:14.760: E/AndroidRuntime(17308):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
04-22 17:00:14.760: E/AndroidRuntime(17308):    at dalvik.system.NativeStart.main(Native Method)

All code are very simple, button exist, but why my app crashing?

Thank's to all.

Answer 1

getView() returns null before onCreateView returns. Move that snippet inside onViewCreated

Answer 2

onCreate() is called before onCreateView() , so you haven't draw the layout when you're trying to get it.

Get the code from onCreate and move it to onViewCreated()

http://developer.android.com/reference/android/app/Fragment.html#Lifecycle

Regards!

Answer 3

can you try something like

 public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
    View content = inflater.inflate(R.layout.inbox_fragment, container, false);
    Button filter_bt;
    filter_bt = (Button) content.findViewById(R.id.filter_button);
    filter_bt.setOnClickListener((OnClickListener) this);
    return content;
}

public void onCreate(Bundle savedInstanceState) 
{
    super.onCreate(savedInstanceState);
}

bcause onCreate is called before onCreateView. It give you a nullpointerexception because your getView() hasn't been defined yet.

Answer 4

I have found problem. There is right code of class:

public class InboxFragment extends Fragment implements View.OnClickListener{
    private ListView ll;
    @Override

    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        return inflater.inflate(R.layout.inbox_fragment, container, false);
    }

    public void onViewCreated(View view, Bundle state)
    {
        super.onViewCreated(view, state);
        Button filter_bt;

        filter_bt = (Button) view.findViewById(R.id.filter_button);
        filter_bt.setOnClickListener(this);
    }

    public void OnClick(View view)
    {

    }

    @Override
    public void onClick(View arg0) {
        // TODO Auto-generated method stub

    }
}