Android自定义视图淡入淡出/延迟动画

Question

I have quite easy class that draws circles. I'm giving the parameter, view calculates the rest. All I want to give some delay and fade effect for each during draw to canvas. I reviewed a few articles about animators and handlers but I couldn't figure out. Please, show me some implementations. Thanks.

    @Override
protected void onDraw(final Canvas canvas) {
    super.onDraw(canvas);
    int w = getWidth();
    int pl = getPaddingLeft();
    int pr = getPaddingRight();
    int totalWidth = w - (pl + pr);
    major = totalWidth / circleCount;
    radius = major / 2;
    startPoint = totalWidth / (circleCount * 2);
    for (int i = 0; i < circleCount; i++) {
        canvas.drawCircle(startPoint + major * i, radius, radius, paint);
    }
}

Answer 1

Here's a simple alpha animation of a button view [it makes the button blink](it's not so hard ;O) ):

import android.view.animation.AlphaAnimation;
import android.view.animation.Animation;
import android.view.animation.LinearInterpolator;

final Animation animation = new AlphaAnimation(1, 0); // Change alpha from fully visible to invisible
animation.setDuration(500); // duration - half a second
animation.setInterpolator(new LinearInterpolator()); // do not alter animation rate
animation.setRepeatCount(Animation.INFINITE);        // Repeat animation infinitely
animation.setRepeatMode(Animation.REVERSE);          // Reverse animation at the end so the button will fade back in

final Button btn = (Button) findViewById(R.id.but4);//replace this with your view
btn.startAnimation(animation);

Answer 2

You could use the setAlpha(int a) method from the Paint class. It should work when you do it on a separate Thread with a little time delay in a loop where you count down from 255 to 0.

Here is a code sample where I tried this for earlier versions of Android some years ago :

private final int FADE_TIME = 10;  // modify to your needs

private void fade() {

    new Thread(new Runnable() {
        @Override
        public void run() {

            try {
                int i = 255;

                while (i >= 0) {

                    paint.setAlpha(i);
                    Thread.sleep(FADE_TIME);
                    i--;
                }


            } catch (InterruptedException e) {
                // do something in case of interruption
            }
        }
    }).start();

}

Nowadays I would probably use a Handler with postDelayed() for this job, but this should give you an impression of how it can be done.