How to animate a path on canvas - android

Question

Is possible to attach an animator to a path? Is there any other way to draw on canvas animated lines? I searched this before i post , but there is nothing about this. In two

Answer 1

You can create a PathMeasure for your path and determine the length of it:

private PathMeasure pathMeasure; // field

// After you've created your path
pathMeasure = new PathMeasure(path, false); 
pathLength = pathMeasure.getLength();

You can then get get a specific point on the path using getPosTan() inside, say, a ValueAnimator's update listener:

final float[] position = new float[2]; // field

// Inside your animation's update method, where dt is your 0..1 animated fraction
final float distance = dt * pathLength;
pathMeasure.getPosTan(distance, position, null);

// If using onDraw you'll need to tell the view to redraw using the new position
invalidate(); 

You can then make use of the position in onDraw (or whatever).

canvas.drawCircle(position[0], position[1], radius, paint);

The advantages of this approach is that it is straightforward, doesn't require chunky maths, and works on all APIs.

If using API 21+, you can use a ValueAnimator and pass in a Path to use its positions, which is simpler. Example SO question.