Pulsating button animation in Android

问题

I'm working with a Voice recognition application and I want to make my play/stop button "pulse" when it's recording. Something like this:

I have tried to make a ScaleAnimation, doing the button grow, but of course, it makes grow all the button.

   public static ObjectAnimator pulseAnimation(ImageView target){

    ObjectAnimator scaleDown = ObjectAnimator.ofPropertyValuesHolder(target,
            PropertyValuesHolder.ofFloat("scaleX", 1.1f),
            PropertyValuesHolder.ofFloat("scaleY", 1.1f));
    scaleDown.setDuration(310);
    scaleDown.setRepeatCount(ObjectAnimator.INFINITE);
    scaleDown.setRepeatMode(ObjectAnimator.REVERSE);

    return scaleDown;
}

So the idea is achieve something like that but just with a alpha behind the actual button. I want to know if it's possible to do this with an alpha animation or something before add a second "Alpha Button" behind my button to make it grow and achieve this effect.

回答1:

Finally I found the solution! I overrided the onDraw method and draw a first circle for my button and, when my boolean is true. I draw a second circle with an alpha as a background. Making a pulsating effect:

 @Override
protected void onDraw(Canvas canvas) {

    int w = getMeasuredWidth();
    int h = getMeasuredHeight();
    mCirclePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    mCirclePaint.setColor(mColor);
    mBackgroundPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    mBackgroundPaint.setColor(Util.adjustAlpha(mColor, 0.4f));
    //Draw circle
    canvas.drawCircle(w/2, h/2, MIN_RADIUS_VALUE , mCirclePaint);        
    if (mAnimationOn) {
        if (mRadius >= MAX_RADIUS_VALUE)
            mPaintGoBack = true;
        else if(mRadius <= MIN_RADIUS_VALUE)
            mPaintGoBack = false;
        //Draw pulsating shadow
        canvas.drawCircle(w / 2, h / 2, mRadius, mBackgroundPaint);
        mRadius = mPaintGoBack ? (mRadius - 0.5f) : (mRadius + 0.5f);
        invalidate();
    }

    super.onDraw(canvas);
}
 public void animateButton(boolean animate){
    if (!animate)
        mRadius = MIN_RADIUS_VALUE;
    mAnimationOn = animate;
    invalidate();
}

来源：https://stackoverflow.com/questions/37263308/pulsating-button-animation-in-android