也许之前下拉刷新你可能会用到一些第三方开源库，如PullToRefresh, ActionBar-PullToRefresh等，但现在已经有官方的组件了---SwipeRefreshLayout
SwipeRefreshLayout是Google在support v4 19.1版本的library更新的一个下拉刷新组件，使用起来很方便，可以很方便的实现Google Now的刷新效果。
Copyright 2014 Storm Zhang
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