blocks|key|4593948|text|正确的方法是在main_queue中使用dispatch_async，就像我在下面的代码中所做的那样|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4593949|dispatch_async(dispatch_get_main_queue(),+{
++++(self.delegate+as+TBGQRCodeViewController).displayQRCode(receiveAddr,+withAmountInBTC:amountBTC)
})|code-block|syntax|javascript|4593950|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

The proper way to do this is to use dispatch_async in the main_queue, as I did in the following code

<pre><code>dispatch_async(dispatch_get_main_queue(), {
 (self.delegate as TBGQRCodeViewController).displayQRCode(receiveAddr, withAmountInBTC:amountBTC)
})
</code></pre>

blocks|key|4593976|text|如果你在闭包中使用self，不要忘记弱化self。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4593977|dispatch_async(dispatch_get_main_queue(),{+[weak+self]+()+->+()+in
++++if+let+strongSelf+=+self+{
++++++++self?.doSomething()
++++}
})|code-block|syntax|javascript|4593978|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Don't forget to weakify self if you are using self inside of the closure.

<pre><code>dispatch_async(dispatch_get_main_queue(),{ [weak self] () -&gt; () in
 if let strongSelf = self {
 self?.doSomething()
 }
})
</code></pre>

blocks|key|87751|text|以下是更好的(IMO)+Swifty/Cocoa样式语法，以实现与其他答案相同的结果：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|87752|NSOperationQueue.mainQueue().addOperationWithBlock({
++++//+Your+code+here
})|code-block|syntax|javascript|87753|或者你可以用更少的代码和更多的功能抓取流行的Async+Swift+library：|offset|length|87754|Async.main+{
++++//+Your+code+here
}|87755|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/duemunk/Async^0|0|0|M|J|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@]|9|@$I|X|J|Y|1|Z]]|A|$]]|$1|K|3|L|5|D|7|10|8|@]|9|@]|A|$E|F]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|T]]]]

Here's the nicer (IMO) Swifty/Cocoa style syntax to achieve the same result as the other answers:

<pre><code>NSOperationQueue.mainQueue().addOperationWithBlock({
 // Your code here
})
</code></pre>

Or you could grab the popular <a href="https://github.com/duemunk/Async" rel="nofollow">Async Swift library</a> for even less code and more functionality:

<pre><code>Async.main {
 // Your code here
}
</code></pre>

blocks|key|87777|text|下面是一个很好的全局函数，您可以添加它以获得更好的语法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|87778|func+dispatch_on_main(block:+dispatch_block_t)+{
++++dispatch_async(dispatch_get_main_queue(),+block)
}|code-block|syntax|javascript|87779|和用法|87780|dispatch_on_main+{
++++//+Do+some+UI+stuff
}|87781|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Here's a nice little global function you can add for a nicer syntax:

<pre><code>func dispatch_on_main(block: dispatch_block_t) {
 dispatch_async(dispatch_get_main_queue(), block)
}
</code></pre>

And usage

<pre><code>dispatch_on_main {
 // Do some UI stuff
}
</code></pre>

blocks|key|87801|text|Swift+3%2B和Swift+4版本：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|87802|DispatchQueue.main.async+{
++++print("Hello")
}|code-block|syntax|javascript|87803|Swift+3和Xcode+9.2：|87804|dispatch_async_on_main_queue+{
++++print("Hello")
}|87805|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Swift 3+ &amp; Swift 4 version:

<pre><code>DispatchQueue.main.async {
 print("Hello")
}
</code></pre>

Swift 3 and Xcode 9.2:

<pre><code>dispatch_async_on_main_queue {
 print("Hello")
}
</code></pre>

blocks|key|87835|text|在主线程上重新加载collectionView|type|unstyled|depth|inlineStyleRanges|entityRanges|data|87836|DispatchQueue.main.async+{
++++self.collectionView.reloadData()
}|code-block|syntax|javascript|87837|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Reload collectionView on Main Thread

<pre><code>DispatchQueue.main.async {
 self.collectionView.reloadData()
}
</code></pre>

blocks|key|87839|text|//Perform+some+task+and+update+UI+immediately.
DispatchQueue.global(qos:+.userInitiated).async+{++
++++//+Call+your+function+here
++++DispatchQueue.main.async+{++
++++++++//+Update+UI
++++++++self.tableView.reloadData()++
++++}
}

//To+call+or+execute+function+after+some+time
DispatchQueue.main.asyncAfter(deadline:+.now()+%2B+5.0)+{
++++//Here+call+your+function
}

//If+you+want+to+do+changes+in+UI+use+this
DispatchQueue.main.async(execute:+{
++++//Update+UI
++++self.tableView.reloadData()
})|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|87840|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>//Perform some task and update UI immediately.
DispatchQueue.global(qos: .userInitiated).async { 
 // Call your function here
 DispatchQueue.main.async { 
 // Update UI
 self.tableView.reloadData() 
 }
}

//To call or execute function after some time
DispatchQueue.main.asyncAfter(deadline: .now() + 5.0) {
 //Here call your function
}

//If you want to do changes in UI use this
DispatchQueue.main.async(execute: {
 //Update UI
 self.tableView.reloadData()
})
</code></pre>

blocks|key|87895|text|您可以使用以下命令切换到主线程|type|unstyled|depth|inlineStyleRanges|entityRanges|data|87896|DispatchQueue.main.async+{
++++++++//+UI+Code+Goes+Here
++++}|code-block|syntax|javascript|87897|您还可以编写更多可重用和可读性更好的代码，我可以通过下面的POP编写自定义协议|87898|protocol+MainThreadRunAble+:+AnyObject+{}|87899|使用扩展实现协议|87900|extension+MainThreadRunAble+{
func+runOnMain(code+:+@escaping()->())+{
++++DispatchQueue.main.async+{
++++++++code()
++++}
}
func+runOnMain(withDelay+delay+:+Float+,code+:+@escaping()->()){
++++DispatchQueue.main.asyncAfter(deadline:+.now()+%2B+delay)+{
+++++++code()
++++}
}}|87901|使您的类符合您希望在主线程上运行的协议|87902|class+YourClass+:+BaseClass,MainThreadRunAble{}|87903|然后根据您的需求调用其中一个方法|87904|runOnMain+{
++++++++//update+on+main
++++}
++++runOnMain(withDelay:+1)+{
++++//update+on+main
++++}|87905|如果您正在使用任何架构，并且只想确保只有viewcontroller可以访问在主线程上运行的这段代码，那么请实现您的扩展|87906|extension+UIViewController+{
func+runOnMain(code+:+@escaping()->())+{
++++DispatchQueue.main.async+{
++++++++code()
++++}
}
func+runOnMain(withDelay+delay+:+Float+,code+:+@escaping()->()){
++++DispatchQueue.main.asyncAfter(deadline:+.now()+%2B+delay)+{
+++++++code()
++++}
}}|87907|entityMap^0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|13|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|14|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|15|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|16|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|17|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|18|8|@]|9|@]|A|$]]|$1|Q|3|R|5|D|7|19|8|@]|9|@]|A|$E|F]]|$1|S|3|T|5|6|7|1A|8|@]|9|@]|A|$]]|$1|U|3|V|5|D|7|1B|8|@]|9|@]|A|$E|F]]|$1|W|3|X|5|6|7|1C|8|@]|9|@]|A|$]]|$1|Y|3|Z|5|D|7|1D|8|@]|9|@]|A|$E|F]]|$1|10|3|-4|5|6|7|1E|8|@]|9|@]|A|$]]]|11|$]]

you can switch to the main thread using
<pre><code>DispatchQueue.main.async {
 // UI Code Goes Here
 }
</code></pre>
you can also write more reusable and readable code my writing you custom protocol by the following POP
<pre><code>protocol MainThreadRunAble : AnyObject {}
</code></pre>
implement protocol using extension
<pre><code>extension MainThreadRunAble {
func runOnMain(code : @escaping()-&gt;()) {
 DispatchQueue.main.async {
 code()
 }
}
func runOnMain(withDelay delay : Float ,code : @escaping()-&gt;()){
 DispatchQueue.main.asyncAfter(deadline: .now() + delay) {
 code()
 }
}}
</code></pre>
conform your class to a protocol where you want to run on the main thread
<pre><code>class YourClass : BaseClass,MainThreadRunAble{}
</code></pre>
then call one of the method based on your requirement
<pre><code>runOnMain {
 //update on main
 }
 runOnMain(withDelay: 1) {
 //update on main
 }
</code></pre>
if you are using any architecture and just want to make sure, only viewcontroller has access to this piece of code to run on the main thread, then implement your extension
<pre><code>extension UIViewController {
func runOnMain(code : @escaping()-&gt;()) {
 DispatchQueue.main.async {
 code()
 }
}
func runOnMain(withDelay delay : Float ,code : @escaping()-&gt;()){
 DispatchQueue.main.asyncAfter(deadline: .now() + delay) {
 code()
 }
}}
</code></pre>

In my app I have a function that makes an NSRURLSession and sends out an NSURLRequest using

<pre><code>sesh.dataTaskWithRequest(req, completionHandler: {(data, response, error)
</code></pre>

In the completion block for this task, I need to do some computation that adds a UIImage to the calling viewcontroller. I have a func called

<pre><code>func displayQRCode(receiveAddr, withAmountInBTC:amountBTC)
</code></pre>

that does the UIImage-adding computation. If I try to run the view-adding code inside of the completion block, Xcode throws an error saying that I can't use the layout engine while in a background process. So I found some code on SO that tries to queue a method on the main thread:

<pre><code>let time = dispatch_time(DISPATCH_TIME_NOW, Int64(0.0 * Double(NSEC_PER_MSEC)))

dispatch_after(time, dispatch_get_main_queue(), {
 let returned = UIApplication.sharedApplication().sendAction("displayQRCode:", to: self.delegate, from: self, forEvent: nil)
})
</code></pre>

However, I don't know how to add the parameters "receiveAddr" and "amountBTC" to this function call. How would I do this, or can someone suggest an optimal way for adding a method call to the application's main queue?

In Swift how to call method with parameters on GCD main thread?

Swift

Xcode

在我的应用程序中，我有一个函数可以生成NSRURLSession并使用以下命令发送NSURLRequestsesh.dataTaskWithRequest(req, completionHandler: {(data, response, error)在这个任务的完成块中，我需要做一些计算，将一个UIImage添加到调...

问在Swift中，如何在GCD主线程上调用带参数的方法？
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问在Swift中，如何在GCD主线程上调用带参数的方法？
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