Android Progressbar: Indeterminate animation without images

I'd like to create an indeterminate animation that simply fades from one color to another (a pulse, if you will). I don't think this should require the use of images but despite 开发者_开发技巧my best efforts, I'm not sure I understand how to use something like AlphaAnimation with a Shape to accomplish this.

Could someone please provide some insight as to how to accomplish this? I have a feeling I'm missing something pretty straightforward here. (Examples are always appreciated!)

Thanks!

This is a trivial task in 3.0 - you can set up an ObjectAnimator to change the "color" or "backgroundColor" of an object (View, ColorDrawable, whatever has the property) between two values. See the ApiDemo animations/BouncingBalls for an example of this.

But assuming you're using pre-3.0 APIs, there are a couple of approaches. First, you could set up your own handler to give you the timing events you need, then calculate the new color at each point.

It's probably slightly easier (if not entirely intuitive) to use an AlphaAnimation. All you really want from the animation is percentage values, not to fade anything. So you don't set the animation on a view, but just set it up to run internally from a value of 0 to 1, then get the current animated value in your onDraw() method and set the current color appropriately.

For example, this will set up and start the alpha animation to run for one second:

Transformation transform = new Transformation();
AlphaAnimation anim = new AlphaAnimation(0f, 1f);
anim.setDuration(1000);
anim.start();

Then in your drawing loop, you grab the current animated value:

long time = getDrawingTime();
anim.getTransformation(time, transform);
float elapsedFraction = transform.getAlpha();

Once you have the elapsedFraction (a value between 0 and 1), you can calculate the appropriate in-between color value.

The code above may not match your situation exactly, but you should be able to do something similar to get what you want.