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
Swift 4有一个很短的方法来做到这一点:
Timer.scheduledTimer(withTimeInterval: 2, repeats: false) { (timer) in
// Your stuff here
print("hello")
}
其他回答
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")
}
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
Swift 3.0版本
以下闭包函数在主线程上执行一些延迟后的任务。
func performAfterDelay(delay : Double, onCompletion: @escaping() -> Void){
DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + delay, execute: {
onCompletion()
})
}
像这样调用这个函数:
performAfterDelay(delay: 4.0) {
print("test")
}
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 3.0中
调度队列
DispatchQueue(label: "test").async {
//long running Background Task
for obj in 0...1000 {
print("async \(obj)")
}
// UI update in main queue
DispatchQueue.main.async(execute: {
print("UI update on main queue")
})
}
DispatchQueue(label: "m").sync {
//long running Background Task
for obj in 0...1000 {
print("sync \(obj)")
}
// UI update in main queue
DispatchQueue.main.sync(execute: {
print("UI update on main queue")
})
}
5秒后调度
DispatchQueue.main.after(when: DispatchTime.now() + 5) {
print("Dispatch after 5 sec")
}