Android How to achieve pulsating circle animation around image view

Question

I am looking to achieve an animation similar to this :

https://dribbble.com/shots/1767235-Rizon-Location-animation

,and with an image view in the circle in the middle.

I understand that a scale animation would be used and I am using this on my circle image view :

<?xml version="1.0" encoding="utf-8"?>
<scale xmlns:android="http://schemas.android.com/apk/res/android"
    android:duration="1000"
    android:fromXScale="1"
    android:fromYScale="1"
    android:pivotX="50%"
    android:pivotY="50%"
    android:repeatCount="infinite"
    android:repeatMode="reverse"
    android:toXScale="0.5"
    android:toYScale="0.5" />

This causes the image to pulsate, but how do I show and animate the rings around the image like the animation above ? Any hints would be helpful.

Thanks !

Answer 1

Override the onDraw method and draw a first circle for your button, creating a boolean variable to control when your button is going to pulse and when is not. Finally draw your 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();
}