Android chronometer timer...

             In this application we will use a chronometer,that will be act as a timer.So we take the xml layout containing a chronometer and three button widget.Here is the xml code for this:

THE XML LAYOUT

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:id="@+id/txt"
    />
    
    <Chronometer 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:id="@+id/chrono"
    />
    
    <Button 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:id="@+id/btnStart"
    android:text="Start"
    android:onClick="onClick"
    />
    
    <Button 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:id="@+id/btnStop"
    android:text="Stop"
    android:onClick="onClick"
    />
    
    <Button 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:id="@+id/btnReset"
    android:text="Reset"
    android:onClick="onClick"
    />
</LinearLayout>

Now we write the java code for this:

Define instances of the controls

 
Chronometer chrono;
Button btnStart;
Button btnStop;
TextView txt;

And some variables 

 
long elapsedTime=0;
String currentTime="";
long startTime=SystemClock.elapsedRealtime();
Boolean resume=false; 

We put the Boolean flag differentiate between starting the Chronometer for the

first time or resuming it after pause.Getting inside the onCreate method:

 
//reference www.androidcookers.co.cc
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
chrono=(Chronometer)findViewById(R.id.chrono);
btnStart=(Button)findViewById(R.id.btnStart);
btnStop=(Button)findViewById(R.id.btnStop);
btnReset=(Button)findViewById(R.id.btnReset);
txt=(TextView)findViewById(R.id.txt); 

Now to handle each button click event:

public void onClick(View v) {
  // TODO Auto-generated method stub
  switch(v.getId())
  {
  case R.id.btnStart:
   btnStart.setEnabled(false);
   btnStop.setEnabled(true);
   if(!resume)
   {
    chrono.setBase(SystemClock.elapsedRealtime());
    chrono.start();
   }
   else
   {   
    chrono.start();
   }   
   break;
  case R.id.btnStop:
   btnStart.setEnabled(true);
   btnStop.setEnabled(false);
   chrono.stop();
   chrono.setText(currentTime);
   resume=true;
   btnStart.setText("Resume");
   break;
  case R.id.btnReset:   
   chrono.stop();
   chrono.setText("00:00");
   resume=false;
   btnStop.setEnabled(false);
   break;
  }
} 

The start button:

The start button can be clicked in two scenarios:

1. Starting the Chronometer for the first time:
   1. We set base of the Chronometer, which is the time in Milliseconds from where the Chronometer starts counting from.
      We set it to SystemClock.elapsedRealtime() Which is the time in Milliseconds since the device boot (equivalent to current time).
   2. then start the Chronometer
2. Resuming the chronometer count after start:
   here we start the chronometer again to resume counting from the value it had when it was stopped.

The stop button:

The stop button pauses the chronometer. And sets the resume flag to true to indicate that the next click on the start button will resume counting [not starting counting from zero].

The Reset button:

The stop button resets the chronometer so the next click on start button will start counting from zero.

The chronometer can implement OnChronometerTickListener interface which requires an implementation of the onChronometerTick method.

The onChronometerTick method handles the Chronometer tick event which occurs every

second.Here’s the implementation of the onChronometerTick method:

chrono.setOnChronometerTickListener(new OnChronometerTickListener()
        {
   public void onChronometerTick(Chronometer arg0) {
    // TODO Auto-generated method stub
    
    if(!resume)
    {
     
     long minutes=((SystemClock.elapsedRealtime()-chrono.getBase())/1000)/60;
     long seconds=((SystemClock.elapsedRealtime()-chrono.getBase())/1000)%60;
     currentTime=minutes+":"+seconds;
     arg0.setText(currentTime);
     elapsedTime=SystemClock.elapsedRealtime();
    }
    else
    {
     
     long minutes=((elapsedTime-chrono.getBase())/1000)/60;
     long seconds=((elapsedTime-chrono.getBase())/1000)%60;
     currentTime=minutes+":"+seconds;
     arg0.setText(currentTime);
     elapsedTime=elapsedTime+1000;
           }   
         }         
     }
  ); 

In this method we handle two scenarios:

1. The chronometer starts for the first time (or from zero):
   The method is invoked every second Here we calculate the difference between the current time(SystemClock.elapsedRealtime) and the time from which the chronometer started counting(chrono.getBase()) and display it.
   Then we store the current time so that when we pause the chronometer we hold the last value of chronometer
   elapsedTime=SystemClock.elapsedRealtime();
2. The chronometer is resumed after stop:
   Here we calculate the difference between the last value of the chronometer (elaspedTime) and the value from which the chronometer started counting (chrono.getBase())
   Then we increment the value of the elapsedTime by 1000 milliseconds (1 second) so that it is update with each tick.

And that was a simple stopwatch or timer using Android Chronometer Control. Sure one can noticed that it is limited to minutes and seconds only. This is because the onTimerTick method is invoked every second so we cannot update the elapsed milliseconds.