CODEWITHSUNDEEP
javaandroidandroid-activity
Keith Pittner
Keith Pittner

Reputation: 37

android - Showing variable changes

Ok - I know there has got to be a simple solution to this but for the life of me I can't figure it out.

Programming a very basic android activity to simply iterate through 0-99. I have a textview that I want to display the count. What happens is that it simply stays blank until the end and then shows the ending count (99).

Not sure if a textview is the right way to display or what the answer is. Any help is greatly appreciated. Thanks in advance

Upvotes: 0

Views: 191

Answers (4)

surender8388
surender8388

Reputation: 474

Use a countdown timer, in below code, onTick() will get called every second, here you can display/update your number each second. set interval according to your need. Its in mili seconds.

public class TimerActivity extends Activity {

private final long startTime = 100 * 1000;
private final long interval = 1 * 1000;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_timer);
    countDownTimer = new MyCountDownTimer(startTime, interval);
    countDownTimer.start();

public class MyCountDownTimer extends CountDownTimer {
    public MyCountDownTimer(long startTime, long interval) {
        super(startTime, interval);
    }

    @Override
    public void onFinish() {
        text.setText("Time's up!");
    }

    @Override
    public void onTick(long millisUntilFinished) {
        text.setText(100 - millisUntilFinished/1000);
    }
}

}

Upvotes: 0

MaciejGórski
MaciejGórski

Reputation: 22232

Try using code like this in onCreate (where number is defined as a field):

textView.post(new Runnable() {
    @Override
    public void run() {
        number++;
        textView.setText("counting: " + number);
        if (number < 100) {
            textView.postDelayed(this, 50);
        }
    }
});

Edit: code was edited as View classes have post and postDelayed, which propagates call to Handler instance they have internally.

You need to read a bit about Handler class.

Warning: this code leaks Activity for the time of approximatelly 5 seconds and should not be used directly in production code. You need to remove Runnable from the message queue at the appropriate time (maybe in onDestroy, but it depends on your needs).

View.removeCallbacks for anti-memory-leak.

Upvotes: 2

Raghunandan
Raghunandan

Reputation: 133560

User a timer scheduled at a fixed rate. Increment a counter every second. Set the text on the UI thread. cancel the timer when required. 

public class MainActivity extends Activity {
TextView _tv;
Timer _t;
int _count=0;


/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    _tv = (TextView) findViewById( R.id.textView1 );
    _t = new Timer();
    _tv.setText(""+_count);
    _t.scheduleAtFixedRate( new TimerTask() {
            @Override
            public void run() {
                _count++;

                runOnUiThread(new Runnable() //run on ui thread
                 {
                  public void run() 
                  { 

                      _tv.setText(""+_count);
                      if(_count==99)
                      {
                          _t.cancel();
                      }
                 }
                 });
            }
        }, 1000, 1000 ); 


    }
@Override
protected void onDestroy() {
    // TODO Auto-generated method stub
    super.onDestroy();

    _t.cancel();
}  
 }

Upvotes: 0

CommonsWare
CommonsWare

Reputation: 1006604

My guess is that your onCreate() has code like this:

for (int i=0;i<100;i++) {
  tv.setText(String.valueOf(i));
  Thread.sleep(100); // or something to delay for a bit
}

That will give you the output that you are describing.

As with many GUI frameworks, Android's UI is event-driven. Calling setText() does not update the screen. Rather, it puts a message on a queue, asking for the screen to be updated. That queue is processed by the main application thread... the same thread that is calling onCreate() in the first place. Hence, what you are doing is queuing up 100 setText() calls, none of which will be processed until your loop is complete. Applying the 100 of them takes very little time, giving the visual result of only seeing the last change.

Upvotes: 2

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