Android中的xml布局的解析是在LayoutInflater中进行的，
LayoutInflater.java

// 这里定义的blink标签
private static final String TAG_1995 = "blink";

LayoutInflater在解析到blink标签时直接返回一个BlinkLayout对象

  private static class BlinkLayout extends FrameLayout {
        private static final int MESSAGE_BLINK = 0x42;
        private static final int BLINK_DELAY = 500;

        private boolean mBlink;
        private boolean mBlinkState;
        private final Handler mHandler;

        public BlinkLayout(Context context, AttributeSet attrs) {
            super(context, attrs);
            mHandler = new Handler(new Handler.Callback() {
                @Override
                public boolean handleMessage(Message msg) {
                    if (msg.what == MESSAGE_BLINK) {
                        if (mBlink) {
                            // 不断的取反，重复操作
                            mBlinkState = !mBlinkState;
                            makeBlink();
                        }
                        invalidate();
                        return true;
                    }
                    return false;
                }
            });
        }

        private void makeBlink() {
            Message message = mHandler.obtainMessage(MESSAGE_BLINK);
            mHandler.sendMessageDelayed(message, BLINK_DELAY);
        }

        @Override
        protected void onAttachedToWindow() {
            super.onAttachedToWindow();

            mBlink = true;
            mBlinkState = true;

            makeBlink();
        }

        @Override
        protected void onDetachedFromWindow() {
            super.onDetachedFromWindow();

            mBlink = false;
            mBlinkState = true;

            mHandler.removeMessages(MESSAGE_BLINK);
        }

        @Override
        protected void dispatchDraw(Canvas canvas) {
            if (mBlinkState) {
                super.dispatchDraw(canvas);
            }
        }
    }

BlinkLayout的作用是每隔500ms绘制刷新一次，也就形成了500ms闪烁的效果，有点类似在EditText中光标不断的闪烁效果。