事件event一般是智能合约中的日志，你每调用一个方法，它执行后会得到什么结果呢：是成功还是失败？这一般可以通过事件来得到确定的答案。虽然在send()方法中有个shouldPollResponse设置为true参数，但是得到它的结果要等待60秒，这时间有点太感人了！回到事件的方法，这估计是确定性的最好方案了。
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