Android App Development 101 4th tutorial; Developing Android StopWatch/Timer

In this tutorial, i will be making a stop watch for android. We will create a text view to display the time elapsed and two buttons one to start the timer and second to stop the timer. We will be using more xml attributes and new java concepts such as runnables and handlers. In addition we will be using android Timer class. Here is our layout:

main.xml


<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

      <TextView
        android:id="@+id/androidtimer"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:text="Android Timer"
        android:textSize="40sp"
        android:textStyle="bold"
        android:textColor="#FF0000"/>
   
    <LinearLayout
        android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal"
    android:gravity="bottom|center" >
    <Button
        android:id="@+id/start"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#FF0000"
        android:text=" start "
        android:textSize="35sp"
        android:textColor="#FFFFFF"
        android:onClick="startTimer"
/>
    <View
        android:layout_width="20dp"
        android:layout_height="1dp"/>
       <Button
        android:id="@+id/stop"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#FF0000"
        android:text=" stop "
        android:textSize="35sp"
        android:textColor="#FFFFFF"
        android:onClick="stopTimer"
       
/>
       </LinearLayout>
</LinearLayout>

The View objects are used just to create some space between two buttons. Also you can see that we have used a new linear layout within a linear layout to display two buttons in a horizontal row.

TimerActivity.java


package com.example.timer;

import java.util.Timer;
import java.util.TimerTask;
import android.os.Bundle;
import android.os.Handler;
import android.app.Activity;
import android.view.View;
import android.widget.TextView;

public class TimerActivity extends Activity {
TimerTask timerTask;
int n=0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}

public void startTimer(View view) {
final Handler handler = new Handler();
Timer ourtimer = new Timer();
timerTask = new TimerTask() {
       public void run() {
               handler.post(new Runnable() {
                       public void run() {
                  TextView timer = (TextView)findViewById(R.id.androidtimer);
               
                  timer.setText(n + " Seconds");
                      n++;
                       }
              });
       }};


   ourtimer.schedule(timerTask, 0, 1000);

}
public void stopTimer(View view) {
timerTask.cancel();
timerTask=null;
n=0;
}

}