Android: Basic Fragments

A simple test using v7 appcomapt library. Tested on 2.3.3 emulator.

fragment.xml

<?xml version="1.0" encoding="utf-8"?>
<SeekBar xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/seekBar"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content" >

</SeekBar>

main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <TextView
        android:id="@+id/timeDisplay"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />

    <fragment
        android:id="@+id/pickerFragment"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        class="com.example.testfragments.TestFragment" >
    </fragment>

</LinearLayout>

MainActivity.java

package com.example.testfragments;

import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.view.Menu;
import android.widget.SeekBar;
import android.widget.TextView;

import com.example.testfragments.TestFragment.OnNumberPickedListener;

/**
 * Updates the value of the {@link TextView} according to the changes in the
 * {@link SeekBar}.
 * 
 * @author dpanayotov
 * 
 */
public class MainActivity extends FragmentActivity implements
		OnNumberPickedListener {
	TextView timeDisplay;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		timeDisplay = (TextView) findViewById(R.id.timeDisplay);
	}

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

	@Override
	public void onNumberPicked(int number) {
		timeDisplay.setText(Integer.toString(number));
	}

}

TestFragment.java

package com.example.testfragments;

import android.app.Activity;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.SeekBar;
import android.widget.SeekBar.OnSeekBarChangeListener;

/**
 * A simple test fragment consisting of just one {@link SeekBar}
 * 
 * @author dpanayotov
 * 
 */
public class TestFragment extends Fragment {

	/**
	 * Must be implemented by the activity to which {@link TestFragment} is
	 * attached. This way the fragment doesn't need to know anything about the
	 * activity. Fragments shouldn't be communicating directly - information
	 * should be handled by the activity.
	 */
	public interface OnNumberPickedListener {
		public void onNumberPicked(int number);
	}

	/**
	 * Keep a reference to the activity to which the fragment is attached
	 * through this field
	 */
	private OnNumberPickedListener listener;

	@Override
	public View onCreateView(LayoutInflater inflater, ViewGroup container,
			Bundle savedInstanceState) {
		// set the layout
		View view = inflater.inflate(R.layout.fragment, container, false);
		// find the number picker and add a value change listener that will call
		// the activity
		SeekBar seekBar = (SeekBar) view.findViewById(R.id.seekBar);
		seekBar.setOnSeekBarChangeListener(new OnSeekBarChangeListener() {

			@Override
			public void onProgressChanged(SeekBar seekBar, int progress,
					boolean fromUser) {
				listener.onNumberPicked(progress);
			}

			@Override
			public void onStartTrackingTouch(SeekBar seekBar) {
			}

			@Override
			public void onStopTrackingTouch(SeekBar seekBar) {
			}

		});
		return view;
	}

	@Override
	public void onAttach(Activity activity) {
		super.onAttach(activity);
		// check if the activity to which the fragment attaches implements the
		// required interface
		if (activity instanceof OnNumberPickedListener) {
			listener = (OnNumberPickedListener) activity;
		} else {
			throw new ClassCastException(activity.toString()
					+ " must implemenet MyListFragment.OnNumberPickedListener");
		}
	}

	@Override
	public void onDetach() {
		super.onDetach();
		listener = null;
	}
}