AnimatableProgressBar.java

public class AnimatableProgressBar extends ProgressBar {

    private ProgressBarAnimation mAnimation;

    public AnimatableProgressBar(Context context) {
        super(context);
        init(context, null);
    }

    public AnimatableProgressBar(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context, attrs);
    }

    public AnimatableProgressBar(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context, attrs);
    }

    public void setProgress(int progress, boolean animate) {
        if (animate) {
            mAnimation.setProgress(progress);
        } else {
            super.setProgress(progress);
        }
    }

    private void init(Context context, AttributeSet attrs) {
        mAnimation = new ProgressBarAnimation(this, 2000);
    }

    public class ProgressBarAnimation extends Animation {

        private ProgressBar mProgressBar;
        private int mTo;
        private int mFrom;
        private final long mStepDuration;

        public ProgressBarAnimation(ProgressBar progressbar, long fullDuration) {
            super();
            Utils.checkNull(progressbar);

            mProgressBar = progressbar;
            mStepDuration = fullDuration / progressbar.getMax();
        }

        public void setProgress(int progress) {
            if (progress < 0) {
                progress = 0;
            } else if (progress > mProgressBar.getMax()) {
                progress = mProgressBar.getMax();
            }

            mTo = progress;

            mFrom = mProgressBar.getProgress();
            setDuration(Math.abs(mTo - mFrom) * mStepDuration);
            mProgressBar.startAnimation(this);
        }

        @Override
        protected void applyTransformation(float interpolatedTime, Transformation t) {
            float value = mFrom + (mTo - mFrom) * interpolatedTime;
            mProgressBar.setProgress((int) value);
        }
    }
}