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三行代码实现一个轮播 BannerView

三行代码实现一个轮播 BannerView

原文链接: www.jianshu.com

自己简单封装了一个带hint的轮播ViewPager,用来展示app首页的Banner,先看效果图吧。


使用起来非常方便~~2至3行代码就能实现上述效果,只要传入一个list就可以(其中是你需要展示的ImageView),当然也可以自己在这基础上添加各种Transform动画。

        bannerView = (BannerView) findViewById(R.id.banner);
        bannerView.setViewList(viewList);
        bannerView.startLoop(true);复制代码

实现原理相信大家应该都知道,就是可能懒得去封装这种东西。

具体思路:

    1. 继承自FrameLayout,在下层填充一个ViewPager
  • 2.根据ViewPager的itemCount去动态生成底部hint小圆点

           if (mLinearPosition.getChildCount() != viewSize) {
                int diffCnt = mLinearPosition.getChildCount() - viewSize;
                boolean needAdd = diffCnt < 0;
                diffCnt = Math.abs(diffCnt);
                for (int i = 0; i < diffCnt; i++) {
                    if (needAdd) {
                        ImageView img = new ImageView(getContext());
                        LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT);
                        layoutParams.rightMargin = getResources().getDimensionPixelOffset(R.dimen.dimen_9dp);
                        img.setLayoutParams(layoutParams);
                        img.setBackgroundResource(R.drawable.banner_point);
                        mLinearPosition.addView(img);
                    } else {
                        mLinearPosition.removeViewAt(0);
                    }
                }
            }复制代码
  • 3.通过Handler去控制轮播的频率,重新设置ViewPager的currentItem以及hint小圆点的背景
private static class BannerHandler extends Handler {
        private WeakReference<BannerView> weakReference = null;

        public BannerHandler(BannerView bannerView) {
            super(Looper.getMainLooper());
            this.weakReference = new WeakReference<BannerView>(bannerView);
        }

        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            if (this.weakReference == null) {
                return;
            }
            BannerView bannerView = this.weakReference.get();
            if (bannerView == null || bannerView.mViewPager == null || bannerView.mViewPager.getAdapter() == null || bannerView.mViewPager.getAdapter().getCount() <= 0) {
                sendEmptyMessageDelayed(MSG_LOOP, LOOP_INTERVAL);
                return;
            }
            int curPos = bannerView.mViewPager.getCurrentItem();
            curPos = (curPos + 1) % bannerView.mViewPager.getAdapter().getCount();
            bannerView.mViewPager.setCurrentItem(curPos);
            sendEmptyMessageDelayed(MSG_LOOP, LOOP_INTERVAL);
        }
    }复制代码
  • 4.具体细节,如无限轮播adapter的创建,handler中的弱引用,启动销毁loop等等

具体源码及demo地址

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Android
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