If your application has a button to cancel a long-running operation but you're doing work in the UI thread, the cancellation event won't be delivered until after the operation has finished!

如果应用程序有一个按钮用于取消某个长时间运行的操作，而您正在使用UI线程执行操作，那么这个取消事件只有到UI线程所做的操作完成后才会被处理！

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