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
另一种方法是像这样扩展Double:
extension Double {
var dispatchTime: dispatch_time_t {
get {
return dispatch_time(DISPATCH_TIME_NOW,Int64(self * Double(NSEC_PER_SEC)))
}
}
}
然后你可以这样使用它:
dispatch_after(Double(2.0).dispatchTime, dispatch_get_main_queue(), { () -> Void in
self.dismissViewControllerAnimated(true, completion: nil)
})
我喜欢matt的延迟函数,但只是出于偏好,我宁愿限制传递闭包。
其他回答
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")
}
更清晰的结构概念:
dispatch_after(when: dispatch_time_t, queue: dispatch_queue_t, block: dispatch_block_t?)
dispatch_time_t为UInt64。dispatch_queue_t实际上是一个NSObject的类型别名,但是你应该使用你熟悉的GCD方法来获取队列。该区块是一个快速关闭。具体来说,dispatch_block_t定义为()-> Void,相当于()->()。
使用示例:
let delayTime = dispatch_time(DISPATCH_TIME_NOW, Int64(1 * Double(NSEC_PER_SEC)))
dispatch_after(delayTime, dispatch_get_main_queue()) {
print("test")
}
编辑:
我推荐使用@matt的延时函数。
编辑2:
在Swift 3中,GCD将会有新的包装器。请看这里:https://github.com/apple/swift-evolution/blob/master/proposals/0088-libdispatch-for-swift3.md
原来的例子在Swift 3中是这样写的:
let deadlineTime = DispatchTime.now() + .seconds(1)
DispatchQueue.main.asyncAfter(deadline: deadlineTime) {
print("test")
}
注意,你可以将deadlineTime声明写为DispatchTime.now() + 1.0,并得到相同的结果,因为+操作符被重写如下(与-类似):
func +(time: DispatchTime, seconds: Double) -> DispatchTime . func +(time: DispatchTime, seconds: Double func +(time: DispatchWalltime, interval: DispatchTimeInterval) -> DispatchWalltime . func +(time: DispatchWalltime, interval: DispatchTimeInterval
这意味着如果您不使用DispatchTimeInterval enum,而只是写一个数字,则假定您使用的是秒。
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
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(10 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
// ...
});
dispatch_after(_:_:_:)函数有三个参数:
延迟 调度队列 块或闭包
dispatch_after(_:_:_:)函数调用在给定延迟后传递给函数的调度队列上的块或闭包。注意,延迟是使用dispatch_time(_:_:)函数创建的。记住这一点,因为我们在Swift中也使用了这个函数。
我建议你通过Raywenderlich调度教程
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
}
}