延迟后如何触发一个块，例如-performSelector：withObject：afterDelay :？

有没有一种方法可以在延迟后使用原始参数来调用块，例如使用，performSelector:withObject:afterDelay:但是使用类似int/ double/ 的参数float？

我认为您正在寻找dispatch_after()。它要求您的块不接受任何参数，但是您可以让该块从本地范围捕获那些变量。

int parameter1 = 12;
float parameter2 = 144.1;

// Delay execution of my block for 10 seconds.
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 10 * NSEC_PER_SEC), dispatch_get_main_queue(), ^{
    NSLog(@"parameter1: %d parameter2: %f", parameter1, parameter2);
});

更多：https：//developer.apple.com/documentation/dispatch/1452876-dispatch_after

您可以dispatch_after稍后使用来调用块。在Xcode中，开始输入内容dispatch_after并点击Enter以自动完成以下操作：

这是一个带有两个浮点数作为“参数”的示例。您不必依赖任何类型的宏，并且代码的意图非常明确：

斯威夫特3，斯威夫特4

let time1 = 8.23
let time2 = 3.42

// Delay 2 seconds
DispatchQueue.main.asyncAfter(deadline: .now() + 2.0) {
    print("Sum of times: \(time1 + time2)")
}

迅捷2

let time1 = 8.23
let time2 = 3.42

// Delay 2 seconds
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, Int64(2.0 * Double(NSEC_PER_SEC))), dispatch_get_main_queue()) { () -> Void in
        println("Sum of times: \(time1 + time2)")
}

目标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);
});

如何使用Xcode内置代码段库？

Swift更新：

许多赞成票启发了我更新这个答案。

内置的Xcode代码段库dispatch_after仅适用于objective-c语言。人们还可以创建自己的自定义代码段的Swift。

用Xcode编写。

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, Int64(<#delayInSeconds#> * Double(NSEC_PER_SEC))), dispatch_get_main_queue(), {
        <#code to be executed after a specified delay#>
    })

将此代码拖放到代码段库区域中。

在代码段列表的底部，将有一个名为的新实体My Code Snippet。编辑此标题。在输入Xcode时提出建议，请填写Completion Shortcut。

有关更多信息，请参见CreationaCustomCodeSnippet。

更新Swift 3

将此代码拖放到代码段库区域中。

DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(<#delayInSeconds#>)) {
    <#code to be executed after a specified delay#>
}

扩展Jaime Cham的答案，我创建了一个NSObject + Blocks类别，如下所示。我觉得这些方法更好地匹配了现有的performSelector:NSObject方法

NSObject + Blocks.h

#import <Foundation/Foundation.h>

@interface NSObject (Blocks)

- (void)performBlock:(void (^)())block afterDelay:(NSTimeInterval)delay;

@end

NSObject + Blocks.m

#import "NSObject+Blocks.h"

@implementation NSObject (Blocks)

- (void)performBlock:(void (^)())block
{
    block();
}

- (void)performBlock:(void (^)())block afterDelay:(NSTimeInterval)delay
{
    void (^block_)() = [block copy]; // autorelease this if you're not using ARC
    [self performSelector:@selector(performBlock:) withObject:block_ afterDelay:delay];
}

@end

并像这样使用：

[anyObject performBlock:^{
    [anotherObject doYourThings:stuff];
} afterDelay:0.15];

也许比通过GCD，在某个地方的某个类（例如，“ Util”）或Object上的类别更简单：

+ (void)runBlock:(void (^)())block
{
    block();
}
+ (void)runAfterDelay:(CGFloat)delay block:(void (^)())block 
{
    void (^block_)() = [[block copy] autorelease];
    [self performSelector:@selector(runBlock:) withObject:block_ afterDelay:delay];
}

如此使用：

[Util runAfterDelay:2 block:^{
    NSLog(@"two seconds later!");
}];

对于Swift，我使用该dispatch_after方法创建了一个全局函数，没什么特别的。我更喜欢它，因为它易于阅读且易于使用：

func performBlock(block:() -> Void, afterDelay delay:NSTimeInterval){
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, Int64(delay * Double(NSEC_PER_SEC))), dispatch_get_main_queue(), block)
}

您可以使用以下方法：

performBlock({ () -> Void in
    // Perform actions
}, afterDelay: 0.3)

这是我的2美分= 5种方法;）

我喜欢封装这些细节，并让AppCode告诉我如何完成句子。

void dispatch_after_delay(float delayInSeconds, dispatch_queue_t queue, dispatch_block_t block) {
    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
    dispatch_after(popTime, queue, block);
}

void dispatch_after_delay_on_main_queue(float delayInSeconds, dispatch_block_t block) {
    dispatch_queue_t queue = dispatch_get_main_queue();
    dispatch_after_delay(delayInSeconds, queue, block);
}

void dispatch_async_on_high_priority_queue(dispatch_block_t block) {
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), block);
}

void dispatch_async_on_background_queue(dispatch_block_t block) {
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), block);
}

void dispatch_async_on_main_queue(dispatch_block_t block) {
    dispatch_async(dispatch_get_main_queue(), block);
}

PerformSelector：WithObject始终带有一个对象，因此为了传递诸如int / double / float等参数。..您可以使用类似这样的东西。

// NSNumber是一个对象。

[self performSelector:@selector(setUserAlphaNumber:)
     withObject: [NSNumber numberWithFloat: 1.0f]       
     afterDelay:1.5];



-(void) setUserAlphaNumber: (NSNumber*) number{

     [txtUsername setAlpha: [number floatValue] ];

}

可以使用[NSNumber numberWithInt：]等相同的方法。在接收方法中，您可以将数字转换为[number int]或[number double]格式。

在给定的时间段后，dispatch_after函数将块对象调度到调度队列。使用以下代码在2.0秒后执行一些与UI相关的任务。

            let delay = 2.0
            let delayInNanoSeconds = dispatch_time(DISPATCH_TIME_NOW, Int64(delay * Double(NSEC_PER_SEC)))
            let mainQueue = dispatch_get_main_queue()

            dispatch_after(delayInNanoSeconds, mainQueue, {

                print("Some UI related task after delay")
            })

在快速3.0中：

            let dispatchTime: DispatchTime = DispatchTime.now() + Double(Int64(2.0 * Double(NSEC_PER_SEC))) / Double(NSEC_PER_SEC)
            DispatchQueue.main.asyncAfter(deadline: dispatchTime, execute: {

          })

这是在延迟后将工作排入队列的Swift 3方法。

DispatchQueue.main.asyncAfter(
  DispatchTime.now() + DispatchTimeInterval.seconds(2)) {
    // do work
}

这是一个方便的帮手，可防止一遍又一遍地发出烦人的GCD呼叫：

public func delay(bySeconds seconds: Double, dispatchLevel: DispatchLevel = .main, closure: @escaping () -> Void) {
    let dispatchTime = DispatchTime.now() + seconds
    dispatchLevel.dispatchQueue.asyncAfter(deadline: dispatchTime, execute: closure)
}

public enum DispatchLevel {
    case main, userInteractive, userInitiated, utility, background
    var dispatchQueue: DispatchQueue {
        switch self {
        case .main:                 return DispatchQueue.main
        case .userInteractive:      return DispatchQueue.global(qos: .userInteractive)
        case .userInitiated:        return DispatchQueue.global(qos: .userInitiated)
        case .utility:              return DispatchQueue.global(qos: .utility)
        case .background:           return DispatchQueue.global(qos: .background)
        }
    }
}

现在，您只需像下面这样在Main线程上延迟代码：

delay(bySeconds: 1.5) { 
    // delayed code
}

如果要延迟代码到其他线程：

delay(bySeconds: 1.5, dispatchLevel: .background) { 
    // delayed code that will run on background thread
}

如果您希望框架也具有更多方便的功能，请签出HandySwift。您可以通过迦太基将其添加到您的项目中，然后像上面的示例一样使用它：

import HandySwift    

delay(bySeconds: 1.5) { 
    // delayed code
}

BlocksKit框架中有一个不错的选择。

方块套件

（和班级）

BBlocksKit.m

在Swift 3中，我们可以简单地使用DispatchQueue.main.asyncAfter函数在延迟“ n”秒后触发任何函数或动作。在这里，我们在代码中设置了1秒后的延迟。您调用此函数体内的任何函数，这些函数将在1秒钟的延迟后触发。

let when = DispatchTime.now() + 1
DispatchQueue.main.asyncAfter(deadline: when) {

    // Trigger the function/action after the delay of 1Sec

}

Xcode 10.2和Swift 5及更高版本

DispatchQueue.main.asyncAfter(deadline: .now() + 2, execute: {
   // code to execute                 
})

您可以将参数包装在您自己的类中，也可以将方法调用包装在不需要以原始类型传递的方法中。然后在延迟后调用该方法，并在该方法内执行您要执行的选择器。

在Swift延迟后，您可以通过以下方法触发一个块：

runThisAfterDelay(seconds: 2) { () -> () in
    print("Prints this 2 seconds later in main queue")
}

/// EZSwiftExtensions
func runThisAfterDelay(seconds seconds: Double, after: () -> ()) {
    let time = dispatch_time(DISPATCH_TIME_NOW, Int64(seconds * Double(NSEC_PER_SEC)))
    dispatch_after(time, dispatch_get_main_queue(), after)
}

它作为标准功能包含在我的仓库中。

Swift 3和Xcode 8.3.2

该代码将为您提供帮助，我也添加了说明

// Create custom class, this will make your life easier
class CustomDelay {

    static let cd = CustomDelay()

    // This is your custom delay function
    func runAfterDelay(_ delay:Double, closure:@escaping ()->()) {
        let when = DispatchTime.now() + delay
        DispatchQueue.main.asyncAfter(deadline: when, execute: closure)
    }
}


// here how to use it (Example 1)
class YourViewController: UIViewController {

    // example delay time 2 second
    let delayTime = 2.0

    override func viewDidLoad() {
        super.viewDidLoad()

        CustomDelay.cd.runAfterDelay(delayTime) {
            // This func will run after 2 second
            // Update your UI here, u don't need to worry to bring this to the main thread because your CustomDelay already make this to main thread automatically :)
            self.runFunc()
        }
    }

    // example function 1
    func runFunc() {
        // do your method 1 here
    }
}

// here how to use it (Example 2)
class YourSecondViewController: UIViewController {

    // let say you want to user run function shoot after 3 second they tap a button

    // Create a button (This is programatically, you can create with storyboard too)
    let shootButton: UIButton = {
        let button = UIButton(type: .system)
        button.frame = CGRect(x: 15, y: 15, width: 40, height: 40) // Customize where do you want to put your button inside your ui
        button.setTitle("Shoot", for: .normal)
        button.translatesAutoresizingMaskIntoConstraints = false
        return button
    }()

    override func viewDidLoad() {
        super.viewDidLoad()

        // create an action selector when user tap shoot button
        shootButton.addTarget(self, action: #selector(shoot), for: .touchUpInside)   
    }

    // example shoot function
    func shoot() {
        // example delay time 3 second then shoot
        let delayTime = 3.0

        // delay a shoot after 3 second
        CustomDelay.cd.runAfterDelay(delayTime) {
            // your shoot method here
            // Update your UI here, u don't need to worry to bring this to the main thread because your CustomDelay already make this to main thread automatically :)
        }
    }   
}

我相信作者不是在问如何等待小数时间（延迟），而是如何将标量作为选择器的参数（withObject :）传递，而现代目标C中最快的方法是：

[obj performSelector:...  withObject:@(0.123123123) afterDelay:10]

您的选择器必须将其参数更改为NSNumber，并使用floatValue或doubleValue之类的选择器来检索值