Ios UILabel未在调度组内更新通知

为什么这不起作用

dispatch_group_notify(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)) { () -> Void in
    println("Howdy, I get called")
    self.myLabel.text = "Hello Mr. Gordon Freeman"
}

---

消息已打印，但未设置UILabel文本。

您只能从主队列更新UI元素：

dispatch_group_notify(group, dispatch_get_main_queue()) {
    println("Howdy, I get called")
    self.myLabel.text = "Hello Mr. Gordon Freeman"
}