How do you trigger a block after a delay, like -pe

Question

Is there a way to call a block with a primitive parameter after a delay, like using performSelector:withObject:afterDelay: but with an argument like int/double/float?

Answer 1

I think you're looking for dispatch_after(). It requires your block to accept no parameters, but you can just let the block capture those variables from your local scope instead.

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);
});

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

Answer 2

You can use dispatch_after to call a block later. In Xcode, start typing dispatch_after and hit Enter to autocomplete to the following:

Here's an example with two floats as "arguments." You don't have to rely on any type of macro, and the intent of the code is quite clear:

Swift 3, Swift 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)")
}

Swift 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)")
}

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);
});

Answer 3

How about using Xcode built-in code snippet library?

Update for Swift:

Many up votes inspired me to update this answer.

The build-in Xcode code snippet library has dispatch_after for only objective-c language. People can also create their own Custom Code Snippet for Swift.

Write this in Xcode.

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#>
    })

Drag this code and drop it in the code snippet library area.

Bottom of the code snippet list, there will be a new entity named My Code Snippet. Edit this for a title. For suggestion as you type in the Xcode fill in the Completion Shortcut.

For more info see CreatingaCustomCodeSnippet.

Update Swift 3

Drag this code and drop it in the code snippet library area.

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

Answer 4

Here's the Swift 3 way to queue work after a delay.

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

Answer 5

Here is how you can trigger a block after a delay in Swift:

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)
}

Its included as a standard function in my repo.

Answer 6

There's a nice one in the BlocksKit framework.

BlocksKit

(and the class)

BBlocksKit.m