我翻遍了苹果的iBook,找不到任何关于它的定义:
有人能解释一下dispatch_after的结构吗?
dispatch_after(<#when: dispatch_time_t#>, <#queue: dispatch_queue_t?#>, <#block: dispatch_block_t?#>)
我翻遍了苹果的iBook,找不到任何关于它的定义:
有人能解释一下dispatch_after的结构吗?
dispatch_after(<#when: dispatch_time_t#>, <#queue: dispatch_queue_t?#>, <#block: dispatch_block_t?#>)
当前回答
现在在Swift的中央调度(GCD)中异步调度不仅仅是语法糖。
添加Podfile
pod 'AsyncSwift'
然后,你可以这样使用它。
let seconds = 3.0
Async.main(after: seconds) {
print("Is called after 3 seconds")
}.background(after: 6.0) {
print("At least 3.0 seconds after previous block, and 6.0 after Async code is called")
}
其他回答
我经常使用dispatch_after,所以我写了一个顶级实用函数来简化语法:
func delay(delay:Double, closure:()->()) {
dispatch_after(
dispatch_time(
DISPATCH_TIME_NOW,
Int64(delay * Double(NSEC_PER_SEC))
),
dispatch_get_main_queue(), closure)
}
现在你可以这样说:
delay(0.4) {
// do stuff
}
哇,一种你可以改进的语言。还有什么比这更好的呢?
更新Swift 3, Xcode 8种子6
看起来几乎不值得费心,现在他们已经改进了调用语法:
func delay(_ delay:Double, closure:@escaping ()->()) {
let when = DispatchTime.now() + delay
DispatchQueue.main.asyncAfter(deadline: when, execute: closure)
}
在swift中使用asyncAfter延迟GCD调用
let delayQueue = DispatchQueue(label: "com.theappmaker.in", qos: .userInitiated)
let additionalTime: DispatchTimeInterval = .seconds(2)
我们可以延迟为**微秒,毫秒,纳秒
delayQueue.asyncAfter(deadline: .now() + 0.60) {
print(Date())
}
delayQueue.asyncAfter(deadline: .now() + additionalTime) {
print(Date())
}
Matt的语法非常好,如果你需要使块失效,你可能想使用这个:
typealias dispatch_cancelable_closure = (cancel : Bool) -> Void
func delay(time:NSTimeInterval, closure:()->Void) -> dispatch_cancelable_closure? {
func dispatch_later(clsr:()->Void) {
dispatch_after(
dispatch_time(
DISPATCH_TIME_NOW,
Int64(time * Double(NSEC_PER_SEC))
),
dispatch_get_main_queue(), clsr)
}
var closure:dispatch_block_t? = closure
var cancelableClosure:dispatch_cancelable_closure?
let delayedClosure:dispatch_cancelable_closure = { cancel in
if closure != nil {
if (cancel == false) {
dispatch_async(dispatch_get_main_queue(), closure!);
}
}
closure = nil
cancelableClosure = nil
}
cancelableClosure = delayedClosure
dispatch_later {
if let delayedClosure = cancelableClosure {
delayedClosure(cancel: false)
}
}
return cancelableClosure;
}
func cancel_delay(closure:dispatch_cancelable_closure?) {
if closure != nil {
closure!(cancel: true)
}
}
使用方法如下
let retVal = delay(2.0) {
println("Later")
}
delay(1.0) {
cancel_delay(retVal)
}
学分
上面的链接似乎坏了。来自Github的原始Objc代码
斯威夫特 3+
这在Swift 3+中是超级简单和优雅的:
DispatchQueue.main.asyncAfter(deadline: .now() + 4.5) {
// ...
}
年长的回答:
为了扩展Cezary的答案,它将在1纳秒后执行,我必须执行以下操作以在4秒半后执行。
let delay = 4.5 * Double(NSEC_PER_SEC)
let time = dispatch_time(DISPATCH_TIME_NOW, Int64(delay))
dispatch_after(time, dispatch_get_main_queue(), block)
编辑:我发现我原来的代码有一点错误。如果不将NSEC_PER_SEC转换为Double类型,隐式类型将导致编译错误。
如果有人能提出一个更优的解决方案,我很乐意听听。
1)添加这个方法作为UIViewController Extension的一部分。
extension UIViewController{
func runAfterDelay(delay: NSTimeInterval, block: dispatch_block_t) {
let time = dispatch_time(DISPATCH_TIME_NOW, Int64(delay * Double(NSEC_PER_SEC)))
dispatch_after(time, dispatch_get_main_queue(), block)
}
}
在VC上调用这个方法:
self.runAfterDelay(5.0, block: {
//Add code to this block
print("run After Delay Success")
})
2)
performSelector("yourMethod Name", withObject: nil, afterDelay: 1)
3)
override func viewWillAppear(animated: Bool) {
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 2), dispatch_get_main_queue(), { () -> () in
//Code Here
})
/ /紧凑的形式
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 2), dispatch_get_main_queue()) {
//Code here
}
}