Android - Textview displaying letters gradually

Question

How do I make a Textview display the text gradually, showing letter by letter? I searched the internet and found some tutorials on Typewriter effect, but I could not use.

main.xml:

<TextView 
android:text="TEXTO"
android:id="@+id/txt"
android:layout_height="wrap_content"
android:layout_width="wrap_content"/>

Mainactivity.java:

TextView txt = (TextView)findViewById(R.id.txt);
Typeface font = Typeface.createFromAsset(getAssets(), "fonts/pixel.ttf");

txt.setTypeface(font);