Fragments Tutorial - Simple 2 - Passing Data

Passing Data between Fragment and host Activity

To pass data from a Fragment to the host Activity we need to Define/declare an Interface and

Implement it on the Activity.

1. Declare an Interface on Fragment_A. 

public interface OnSomethingSelectedListener {
    public void passData(int position);
      }  

2. onAttach() : To be sure that Activity implements the Interface  onAttach callback method of Fragment_A  we instantiate an Instance of Ιnterface by casting the Activity  passed into onAttach().
The Fragment captures the interface implementation during its onAttach() lifecycle method and can then call the Interface methods in order to communicate with the Activity.

@Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        
        // This makes sure that the container activity has implemented the callback interface. If not, it throws an exception
        try {
            listener = (OnSomethingSelectedListener) activity;
        } catch (ClassCastException e) {
            throw new ClassCastException(activity.toString()
                    + " must implement OnHeadlineSelectedListener");
        }
    }

3. On Main Activity we implement the Interface like this :

public class MainActivity extends FragmentActivity implements OnSomethingSelectedListener

@Override
public void passData(int position) {
 Log.d(TAG, "Give me the result  " + position  );
 position = position +1;
 Log.d(TAG, "Give me the result  " + position  ); 
}

We just take the integer value parameter from the Fragment and add one to it.



4. A button on Fragment's layout so we can add onClick event

 

<button 
android:id="@+id/button_id" 
android:layout_height="wrap_content" 
android:layout_width="wrap_content" 
android:text="send Integer">
</button>

5. And on Fragment's onCreateView() we add the listener for the event:

Button button = (Button) view.findViewById(R.id.button_id);
    button.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            Log.v(TAG, "onClick 1");
            listener.passData(5); //pass an Integer
        }
    });

We pass the value five to the method passData() Now when we click on the Button we open LogCat View and we see that value one has been added to the  value  of the parameter:

Fragments Simple Example - Version 1

We will make an Activity that will display 2 fragments in its layout.
One fragment will be above the other just like the screen. Both fragments will be of the TextView type and will display text.

So here is what we 're going to have:

Where in the above image is shown the TextView that we are going to define in the layout for Fragment A and respectively down the TextView in layout for Fragment B.

public class Fragment_A extends Fragment {

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

          return inflater.inflate(R.layout.fragment_a_layout, container, false);

     }
}

and the fragment_a_layout as we said is a TextView :

<linearlayout 
    android:layout_height="match_parent" 
    android:layout_width="match_parent" 
    android:orientation="vertical" 
    xmlns:android="http://schemas.android.com/apk/res/android">
    
<textview 
    android:id="@+id/tv" 
    android:layout_height="wrap_content" 
    android:layout_width="fill_parent" 
    android:text="Fragment A">
</linearlayout>

Respectively we make up the class for the Fragment B and layout as fragment_a_layout. Now what's left is to bind the 2 fragments on Activity's layout.

main_layout:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainLayoutActivity" >

    
      <fragment 
          android:name="org.example.fragmentsapp.Fragment_A"
          android:id="@+id/id_frag_A"
          android:layout_width="100dp"
          android:layout_height="50dp"
          android:layout_marginBottom="20dp" />

      <fragment
          android:id="@+id/id_frag_B"
          android:name="org.example.fragmentsapp.Fragment_B"
          android:layout_width="100dp"
          android:layout_height="50dp"
          android:layout_below="@id/id_frag_A" />

</RelativeLayout>

What you must take care is that we use RelativeLayout because its much more dynamic and flexible than LinearLayout and thats something we are going to need for the next Fragment Tutorials.
Also every <fragment> element has its own name, ie for Fragment A we call it as android:name="org.example.fragmentsapp.Fragment_A" and the same for B. Later when we are going to use them inside the Activity scope that will be based on the id we have define.

So our Activity is :

package org.example.fragmentsapp;

import android.os.Bundle;
import android.support.v4.app.FragmentActivity;

public class MainLayoutActivity extends FragmentActivity {

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

Keep in mind that we refer also to APIs lower than API 11 so we extend FragmentActivity and not Activity.
If you target device with android 3.0 or later then you can change FragmentActivity with Activity.


FragmentActivity is something that we can use because of the  Support library