DispatchWorkItem通知主线程 [英] DispatchWorkItem not notifying main thread

问题描述

注意:这不是重复的问题，我已经见过调度组-无法通知主线程

Note: This is not duplicate question I have already seen Dispatch group - cannot notify to main thread

关于 DispatchWorkItem

我有如下代码

let dwi3 = DispatchWorkItem {
    print("start DispatchWorkItem \(Thread.isMainThread)")
    sleep(2)
    
    print("end DispatchWorkItem")
}
let myDq = DispatchQueue(label: "A custom dispatch queue")
dwi3.notify(queue: myDq) {
    print("notify")

}
DispatchQueue.global().async(execute: dwi3)

哪个工作正常(我可以在控制台上看到通知)，而不是在主线程中启动DispatchWorkItem false

Which is working correctly (I can see notify on console) and not in main thread start DispatchWorkItem false

启动DispatchWorkItem为假

start DispatchWorkItem false

结束DispatchWorkItem

end DispatchWorkItem

通知

现在我正尝试使用通知主线程

Now I am trying to notify to main thread using

dwi3.notify(queue: DispatchQueue.main) {
    print("notify")

}

但是它从未调用过，我已经阅读并发现，如果Thread被阻塞，则会发生这种情况.但是我已经在DispatchQueue.global()

But it never calls , I have read and found that if Thread is blocked then situation occurs. but i am already executing DisptachWorkItem in DispatchQueue.global()

请问有人可以在这方面帮助我吗?

Please Anyone can help me on this that what actually going on ?

推荐答案

如果您正在操场上运行异步代码，则需要启用不确定的执行，否则执行可能会在回调执行之前结束.

If you are running asynchronous code in a playground then you need to enable indefinite execution, otherwise execution may end before the callbacks execute.

在操场上的代码中添加以下行:

Add the following lines to your code in the playground:

import PlaygroundSupport
PlaygroundPage.current.needsIndefiniteExecution = true

执行此操作后，您将看到通知在主队列上正确执行.

Once you do this, you will see that the notify executes correctly on the main queue.

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