Adding Delay In A For Loop Without Blocking UI - ios

Question

In my UI, when a button is tapped, it calls a for loop that executes several tasks sequentially.
// For Loop
for (int i = 1; i <= 3; i++)
{
// Perform Task[i]
}
// Results:
// Task 1
// Task 2
// Task 3
After each task, I would like add a user-defined delay. For example:
// For Loop
for (int i = 1; i <= 3; i++)
{
// Perform Task[i]
// Add Delay Here
}
// Results:
//
// Task 1
// Delay 2.5 seconds
//
// Task 2
// Delay 3 seconds
//
// Task 3
// Delay 2 seconds
In iOS, using Objective-C, is there a way to add such delays within a for loop, keeping in mind:
The UI should remain responsive.
The tasks must be performed in order, sequentially.
A code example within the context of a for loop would be most helpful. Thank you.

Answer 1

Use GCD dispatch_after.
You can search its usage on stackoverflow.
Nice article is here
Brief example in Swift for 1.5 seconds delay:
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, Int64(Double(NSEC_PER_SEC) * 1.5)), dispatch_get_main_queue()) {
// your code here after 1.5 delay - pay attention it will be executed on the main thread
}
and objective-c:
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1.5 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^ {
// your code here after 1.5 delay - pay attention it will be executed on the main thread
});

Answer 2

This sounds like an ideal job for NSOperationQueue with the delay being implemented like this:
#interface DelayOperation : NSOperation
#property (NSTimeInterval) delay;
- (void)main
{
[NSThread sleepForTimeInterval:delay];
}
#end

Answer 3

Would this solution work? Instead of using dispatch_after, I use dispatch_async with a [NSThread sleepForTimeInterval] block, which allows me to put a delay anywhere that I need in my custom queue.
dispatch_queue_t myCustomQueue;
myCustomQueue = dispatch_queue_create("com.example.MyQueue", NULL);
dispatch_async(myCustomQueue, ^ {
NSLog(#“Task1”);
});
dispatch_async(myCustomQueue, ^ {
[NSThread sleepForTimeInterval:2.5];
});
dispatch_async(myCustomQueue, ^ {
NSLog(#“Task2”);
});
dispatch_async(myCustomQueue, ^ {
[NSThread sleepForTimeInterval:3.0];
});
dispatch_async(myCustomQueue, ^ {
NSLog(#“Task3”);
});
dispatch_async(myCustomQueue, ^ {
[NSThread sleepForTimeInterval:2.0];
});

Answer 4

Heres a Swift version:
func delay(seconds seconds: Double, after: ()->()) {
delay(seconds: seconds, queue: dispatch_get_main_queue(), after: after)
}
func delay(seconds seconds: Double, queue: dispatch_queue_t, after: ()->()) {
let time = dispatch_time(DISPATCH_TIME_NOW, Int64(seconds * Double(NSEC_PER_SEC)))
dispatch_after(time, queue, after)
}
How you call it:
print("Something")
delay(seconds: 2, after: { () -> () in
print("Delayed print")
})
print("Anotherthing")