循环不起作用，为什么会这样？

Question

I am having trouble understanding this java code. I want the image to twinkle a couple of times, with some delay. The image twinkle once and thats it. Can someone give me an explanation would be great!

private void RunAnimations(int[]melodiTakten) { 

    for (int i = 0; i < 4; i++) {  

        ImageView markeringspilen = (ImageView) findViewById(R.id.markeringspil);
        markeringspilen.setVisibility(View.VISIBLE);
        markeringspilen.postDelayed(new Runnable() {
            public void run() {
                ImageView markeringspilen = (ImageView) findViewById(R.id.markeringspil);

                markeringspilen.setVisibility(View.INVISIBLE);
            }
        }, 2000);

    } 

Answer 1

If I understand your idea right, your implementation is wrong in that it sets delayed actions to take place all at the same time. You can space them out like this:

for (int i = 0; i < 4; i++) {
    markeringspilen.postDelayed(new Runnable() {
        public void run() {
            ImageView markeringspilen = (ImageView) findViewById(R.id.markeringspil);
            markeringspilen.setVisibility(View.VISIBLE);
        }
    }, 4000*i);
    markeringspilen.postDelayed(new Runnable() {
        public void run() {
            ImageView markeringspilen = (ImageView) findViewById(R.id.markeringspil);
            markeringspilen.setVisibility(View.INVISIBLE);
        }
    }, 4000*i+2000);
}

This loop sets up eight delayed visibility changes - a group of four pairs of set visible at 4000*i followed by set invisible at 4000*i+2000 .

Answer 2

the loop is executed, but it's executed very fast and you can't see it. You should put some delay in the loop, not only in the runnable.

Answer 3

That's because you call setVisibility(View.VISIBLE) four times in a row and then, after a 2s delay, four times setVisibility(View.INVISIBLE) .

What you need to do is add eight runnables with ever increasing delays that in turn toggle the visibility.