Question

I am currently learning how to develop applications for Android mobile devices.

I wrote a test application to display numbers 0-9 on the device screen. I created a simple function to delay the number change.

However, upon running the application, only the final number is displayed. There is also a delay before this final number shows. I’m assuming that the length of the pause is my defined delay multiplied by the number of digits to be shown.

How do I create an app that changes the numbers with a delay?

public class AndroidProjectActivity extends Activity {
    public void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        Main();
    }

void Delay(int Seconds){
    long Time = 0;
    Time = System.currentTimeMillis();
    while(System.currentTimeMillis() < Time+(Seconds*1000));
}

void Main() {
    String ConvertedInt;
    TextView tv = new TextView(this);
    setContentView(tv);

    for(int NewInt = 0; NewInt!= 9; NewInt++){
        ConvertedInt = Character.toString((char)(NewInt+48));
        tv.setText(ConvertedInt);
        Delay(5);
    }
}

Answer 1

One way of doing this is to create a runnable that updates your view. This will still update on the UI thread, but wait in the background. There might be mistakes in the below code, but it should run with minor tweaks..

Blocking in any of the system calls into your activity is not good, since you’re blocking the UI thread. Your app will be force closed, with an Application Not Responding message. Here is another good example.

public class AndroidProjectActivity extends Activity {
    private Handler mHandler;
    private TextView mTextView;
    private Runnable mCountUpdater = new Runnable() {
        private int mCount = 0;
        run() {
           if(mCount > 9)
               return;
           mTextView.setText(String.valueOF(mCount+48));
           mCount++;
           // Reschedule ourselves.
           mHandler.postDelayed(this, 5000);
        }
    }
    public void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        // Cleaner to load a view from a layout..
        TextView tv = new TextView(this);
        setContentView(tv);
        mTextView = tv;
        // Create handler on UI thread.
        mHandler = new Handler();
        mHandler.post(mCountUpdater);
    }
}