Question

Anyone knows any efficient method of perform an animation that what is has to do is to display a text, character by character? Like:

T
Th
Thi
This
This i
This is
…

And so on.

Thanks!

Answer 1

This may not be the most elegant solution, but the simplest is probably a quick subclass of TextView with a Handler that updates the text every so often until the complete sequence is displayed:

public class Typewriter extends TextView {

    private CharSequence mText;
    private int mIndex;
    private long mDelay = 500; //Default 500ms delay
    
    
    public Typewriter(Context context) {
        super(context);
    }
    
    public Typewriter(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    
    private Handler mHandler = new Handler();
    private Runnable characterAdder = new Runnable() {
        @Override
        public void run() {
            setText(mText.subSequence(0, mIndex++));
            if(mIndex <= mText.length()) {
                mHandler.postDelayed(characterAdder, mDelay);
            }
        }
    };
    
    public void animateText(CharSequence text) {
        mText = text;
        mIndex = 0;
        
        setText("");
        mHandler.removeCallbacks(characterAdder);
        mHandler.postDelayed(characterAdder, mDelay);
    }
    
    public void setCharacterDelay(long millis) {
        mDelay = millis;
    }
}

You can then use this in an Activity like so:

public class MyActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Typewriter writer = new Typewriter(this);
        setContentView(writer);

        //Add a character every 150ms
        writer.setCharacterDelay(150);
        writer.animateText("Sample String");
    }
}

If you want some animation effects with each letter added, perhaps look at subclassing TextSwitcher instead.