null pointer exception with Fragments and EventBus

Question

I have gone through various methods to make this project work and have finally settled on EventBus from Green Robot. My second question in relation to this on here is here:-Multiple Fragment to Activity communication.

I was directed down the Event Bus route there. I have bolted in he appropriate Libraries and I think I am very close to making it work. I keep getting a null pointer exception at whatever line contains the

eBus.post(Str);

I am fairly certain it in because I a not registering the eBus correctly. I know a Fragment doesn't have a context as such, but I have also tried to use getActivity() as well to no avail. I have posted the MainActivity, CoreFragment and LogCat below. If anyone can help I would greatly appreciate it. This has been ongoing, on and off for nearly a month!!

import de.greenrobot.event.EventBus;
import android.os.Bundle;
import android.app.Activity;
import android.util.Log;
import android.view.Menu;
import android.widget.EditText;

public class MainActivity extends Activity {

EditText editText1;
String Txt;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    editText1 = (EditText) findViewById(R.id.editText1);
    Txt = "";
    EventBus eBus = new EventBus();
    eBus.register(this);<--This I removed.
        eBus.getDefault().register(this);<--This is the new line you suggested  
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.activity_main, menu);
    return true;
}

public void onEvent(String event){
    Txt = Txt + event;
    editText1.setText(Txt);<--Left this as it was,it worked
}


}//End

Here is the Fragment Code:

import de.greenrobot.event.EventBus;
import android.app.Activity;
import android.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.os.Bundle;
import android.widget.Button;
import android.widget.RelativeLayout;
import android.view.View.OnClickListener;


public class CoreFragment extends Fragment{

int index;
Button Button1,Button2,Button3;
String Str,data;
EventBus eBus;


@Override
public void onAttach(Activity a) {
    super.onAttach(a);
    EventBus eBus = new EventBus();
    eBus.getDefault().register(this);
    }


public static CoreFragment newInstance(int index) {
    CoreFragment coreFragment = new CoreFragment();
    coreFragment.index = index;
    return coreFragment;
}

public void onEvent(String event){
// Crash Stopper
    }   

public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {


    if (container == null) {
        // We have different layouts, and in one of them this
        // fragment's containing frame doesn't exist. The fragment
        // may still be created from its saved state, but there is
        // no reason to try to create its view hierarchy because it
        // won't be displayed. Note this is not needed -- we could
        // just run the code below, where we would create and return
        // the view hierarchy; it would just never be used.
        return null;
    }
    RelativeLayout mRelativeLayout = (RelativeLayout) inflater.inflate(R.layout.corefragment,
            container, false);

    Button Button1 = (Button) mRelativeLayout.findViewById(R.id.Button1);
    Button Button2 = (Button) mRelativeLayout.findViewById(R.id.Button2);
    Button Button3 = (Button) mRelativeLayout.findViewById(R.id.Button3);

    Button1.setOnClickListener(new OnClickListener() {
    @Override
    public void onClick(View v) {
    Str = "I ";
    eBus.post(Str);<--Old code, removed in working version
        eBus.getDefault().post(Str);<--Changed as suggested
    }

         });

    Button2.setOnClickListener(new OnClickListener() {
    @Override
    public void onClick(View v) {
        Str = "want ";
    eBus.post(Str);<--Old code, removed in working version
        eBus.getDefault().post(Str);<--Changed as suggested
    }

         });

    Button3.setOnClickListener(new OnClickListener() {
    @Override
    public void onClick(View v) {
        Str = "more ";
    eBus.post(Str);<--Old code, removed in working version
        eBus.getDefault().post(Str);<--Changed as suggested
    }

         });

    return mRelativeLayout;
}


}//end

I have tried various permutations, such as eBus.register(this);, eBus.register(this, String.Class);, eBus.register(getActivity()); etc. Here is the LogCat for when Button 1 is pressed:-

02-13 13:56:40.717: W/dalvikvm(26237): threadid=1: thread exiting with uncaught exception (group=0x40acf228)
02-13 13:56:40.747: E/AndroidRuntime(26237): FATAL EXCEPTION: main
02-13 13:56:40.747: E/AndroidRuntime(26237): java.lang.NullPointerException
02-13 13:56:40.747: E/AndroidRuntime(26237):    at com.epsilonitsystems.fragger.CoreFragment$1.onClick(CoreFragment.java:65)
02-13 13:56:40.747: E/AndroidRuntime(26237):    at android.view.View.performClick(View.java:3549)
02-13 13:56:40.747: E/AndroidRuntime(26237):    at android.view.View$PerformClick.run(View.java:14393)
02-13 13:56:40.747: E/AndroidRuntime(26237):    at android.os.Handler.handleCallback(Handler.java:605)
02-13 13:56:40.747: E/AndroidRuntime(26237):    at android.os.Handler.dispatchMessage(Handler.java:92)
02-13 13:56:40.747: E/AndroidRuntime(26237):    at android.os.Looper.loop(Looper.java:154)
02-13 13:56:40.747: E/AndroidRuntime(26237):    at android.app.ActivityThread.main(ActivityThread.java:4945)
02-13 13:56:40.747: E/AndroidRuntime(26237):    at java.lang.reflect.Method.invokeNative(Native Method)
02-13 13:56:40.747: E/AndroidRuntime(26237):    at java.lang.reflect.Method.invoke(Method.java:511)
02-13 13:56:40.747: E/AndroidRuntime(26237):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
02-13 13:56:40.747: E/AndroidRuntime(26237):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
02-13 13:56:40.747: E/AndroidRuntime(26237):    at dalvik.system.NativeStart.main(Native Method)

All the various methods I have tried compile fine with no errors but Force Close ever time I press a button on screen. Any ideas anyone please?? Thank You.

Answer 1

Try the following suggestions:

1. Anywhere you are registering to the event bus use:

EventBus.getDefault().register(this);

2. When you want to post an event use:

EventBus.getDetault().post(new MyEvent(aString));

3. If you are going to make a change to the UI be sure to name your event method as follows:

 public void onEventMainThread(MyEvent event){
        editText1.setText(event.getString());
    }

4. Define an event Class to hold the result:

public class MyEvent(){
  private mString;

  public MyEvent(String string){
    mString = string;
  }

  public getString(){
    return mString;
  }
}

5. Dont forget to unregister your components from the EventBus by calling:

EventBus.getDefault().unregister(this);