将数据从片段传递到另一个具有相同活动的片段

Question

im trying to send data from fragment 1, to fragment 2.

Im getting a NullPointerException , and i dont quite know why..

I have searched on google and found a lot of articles about, what im trying to do, but i just cant figure out how the general way is done, and if its even possible=(

sorry for using bad english, and im a beginner so...

Code used in Fragment 1

  public interface DataMessage {
        public void send(String message);


   }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
try {SM = (DataMessage)activity;
    }catch (ClassCastException e){
throw new ClassCastException("Implement message interface");
}

Code Used in Fragment 2

  public void getData(String message){
        edt.setText(message);
        Log.i("Disp", "ListHistoryFragment " + message);
    }

Code used in Activity

public class MyActivity extends ActionBarActivity
        implements NavigationDrawerFragment.NavigationDrawerCallbacks, ListHistoryFragment.DataMessage
        ...




  @Override
    public void send(String message) {
        //DisplayFragment DispFrag = (DisplayFragment) getSupportFragmentManager().findFragmentById(R.id.fragmenttest);
        DisplayFragment DispFrag = new DisplayFragment();

        FragmentTransaction Transfer = getSupportFragmentManager().beginTransaction();
        DispFrag.getData(message);
        Transfer.replace(R.id.container, DispFrag).addToBackStack(null).commit();

        Log.i("Acitivyt", "ListHistoryFragment " + message);


    }

Log Cat:

 1-22 11:39:01.580  22399-22399/rampanere.packed.package.nl E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.NullPointerException
            at android.rampa.pack.nl.SQL.DisplayFragment.getData(DisplayFragment.java:152)
            at android.rampa.pack.nl.MyActivity.send(MyActivity.java:265)
            at android.rampa.pack.nl.SQL.ListHistoryFragment$1.onItemClick(ListHistoryFragment.java:73)

EDIT:

lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                @Override
                public void onItemClick(AdapterView<?> parent, View view,
                                        int position, long id) {

                    SM.send(message);
                }

Answer 1

To share data between fragments and activities you should keep an instance of the data you are planning to share in your activity. SharedPreferences are intended to other purposes, for example, storing data that you will need whenever your application starts.

Inside your activity declare a protected/public String called message for example.

public class MyActivity extends .... {

    public String message;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        ...
}

Inside your first fragment, whenever you want to save your String use.

((NAMEOFYOURACTIVITY) getActivity()).message = "THE STRING YOU WANT TO SHARE";

Inside your second fragment, to retrieve your message use:

((NAMEOFYOURACTiIVTY) getActivity()).message;

For example:

Log.i("The string in","my activity is: "+((NAMEOFYOURACTiIVTY) getActivity()).message);