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
这对我很管用。
斯威夫特3:
let time1 = 8.23
let time2 = 3.42
// Delay 2 seconds
DispatchQueue.main.asyncAfter(deadline: .now() + 2.0) {
print("Sum of times: \(time1 + time2)")
}
objective - c:
CGFloat time1 = 3.49;
CGFloat time2 = 8.13;
// Delay 2 seconds
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
CGFloat newTime = time1 + time2;
NSLog(@"New time: %f", newTime);
});
其他回答
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")
}
Swift 3.0 & Swift 4.0 & Swift 5.0中最简单的解决方案
func delayWithSeconds(_ seconds: Double, completion: @escaping () -> ()) {
DispatchQueue.main.asyncAfter(deadline: .now() + seconds) {
completion()
}
}
使用
delayWithSeconds(1) {
//Do something
}
在Swift 5中,在下面使用:
DispatchQueue.main.asyncAfter(deadline: .now() + 0.2, execute: closure)
// time gap, specify unit is second
DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(2)) {
Singleton.shared().printDate()
}
// default time gap is second, you can reduce it
DispatchQueue.main.asyncAfter(deadline: .now() + 0.2) {
// just do it!
}
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
}
}
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")
}