实现图片轮播的几种方法

思路：开启一个子线程，在子线程中设置当前页卡的位置并向主线程中发送消息，每隔一定的时间间隔执行一次子线程，然后和handler接收子线程发过来的消息，并在这里刷新UI（设置当前位置的图片）。

1.使用timer实现

timer = new Timer();
        timer.schedule(new TimerTask() {
            @Override
           public void run() {
               currentItem = (currentItem +1) % imageViews.size();
                handler.sendEmptyMessage(0);
            }
        },2000,2000);
        handler = new Handler(new Handler.Callback() {
            @Override
            public boolean handleMessage(Message msg) {
                viewPager.setCurrentItem(currentItem);
                return false;
            }
        });

2.使用Thread实现：这里在run方法里为了能一直使图片轮播，所以把把要执行的任务放在死循环里

new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    while (true){
                    Thread.sleep(2000);
                    currentItem = (currentItem + 1) % imageViews.size();
                    handler.sendEmptyMessage(0);
                    }
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }).start();
        handler = new Handler(new Handler.Callback() {
            @Override
            public boolean handleMessage(Message msg) {
                viewPager.setCurrentItem(currentItem);
                return false;
            }
        });

3.使用线程池实现：首先在onStrat方法里开启线程池，scheduledExecutorService的scheduleWithFixedDelay方法里的参数是
1.子线程，2.初次执行时间，3.时间间隔，4.时间单位

@Override
    protected void onStart() {
        super.onStart();
        ScheduledExecutorService scheduledExecutorService = Executors.newSingleThreadScheduledExecutor();
        scheduledExecutorService.scheduleWithFixedDelay(new MyRunnable(),2,2, TimeUnit.SECONDS);
        // 或者用下面一种，效果是一样的
        ScheduledExecutorService scheduledExecutorService = Executors.newSingleThreadScheduledExecutor();
        scheduledExecutorService.scheduleAtFixedRate(new MyRunnable(),2,2,TimeUnit.SECONDS);
    }

    public class MyRunnable implements Runnable{

        @Override
        public void run() {
            currentItem = (currentItem + 1)%imageViews.size();
            handler.sendEmptyMessage(0);
        }
    }

刷新UI的代码

private Handler handler = new Handler(new Handler.Callback() {
        @Override
        public boolean handleMessage(Message msg) {
            viewPager.setCurrentItem(currentItem);
            return false;
        }
    });