Apps Android graphics: How does TransitionDrawable work?

[soBinary]

I read the documentation but I can't manage to make a transition occur. What's the flow of events supposed to be like? Who calls who?

Suppose I wanted to have an activity call init() to draw line a, and call go to make a 5 second transition to line b. What would I have to do to this code?


public class Fun extends View
{
Drawable a;
Drawable b;
TransitionDrawable t;
public Fun(Context context)
{
super(context);
a = new LineA();
b = new LineB();
Drawable ray[] = {a,b};
t = new TransitionDrawable( ray );
}

@Override
protected void onDraw(Canvas canvas)
{
t.draw(canvas);

}

public void init()
{
t.resetTransition();
}

public void go()
{
t.startTransition(5000);
}