Delay for all value in loop

Question

Once the button is tapped after a delay of 5 seconds the total values in the array gets executed.

- (IBAction)testButton:(id)sender {
NSArray *array = [NSArray arrayWithObjects:
                      @"Hefeweizen", @"IPA", @"Pilsner", @"Stout", nil];


for (NSIndexPath *anIndexPath in array) {




        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 5 * NSEC_PER_SEC), dispatch_get_main_queue(), ^{


             NSLog(@"INDEX PATH %@",anIndexPath);



        }); 
}

How to create delay of 5 sec (given) for every value inside the array ?

See this thread: http://stackoverflow.com/questions/2232366/waiting-for-a-specified-duration-in-cocoa — Romain, Jan 31 '15 at 11:36
That code is nonsense. The array contains NSString objects, not NSIndexPath objects. — gnasher729, Jan 31 '15 at 13:59

score 2 · Answer 1 · answered Jan 31 '15 at 11:50

When you iterate over the array, your dispatch_after() calls will happen in a very short time frame, so their blocks with the NSLog() will later be executed at pretty much the same time as well.

Depending on what you are trying to achieve and the precision you need, you could do something as simple as scheduling each block 5 sec later at the time when you iterate over the array:

int64_t interval = 0;
for (NSIndexPath *anIndexPath in array) {
    dispatch_time_t start = DISPATCH_TIME_NOW;
    interval += 5;
    dispatch_after(dispatch_time(start, interval * NSEC_PER_SEC), dispatch_get_main_queue(), ^{
        NSLog(@"INDEX PATH %@",anIndexPath);
    }); 
}

In this example, the first block will be scheduled in 5 sec, the second in 10 sec, the third in 15 sec, and so on.

score 2 · Answer 2 · answered Jan 31 '15 at 16:58

You can easily queue the execution one after another:

- (void)executeFirstInArray:(NSArray *)array {
   NSString *firstItem = [array firstObject];
   array = [array subarrayWithRange:NSMakeRange(1, array.count - 1)];

   NSLog(@"Item: %@", firstItem);

   if (array.count > 0) {
      [self performSelector:_cmd withObject:array afterDelay:5.0];
   }
}

- (IBAction)testButton:(id)sender {
    NSArray *array = [NSArray arrayWithObjects:
                   @"Hefeweizen", @"IPA", @"Pilsner", @"Stout", nil];

   [self performSelector:@selector(executeFirstInArray:) withObject:array afterDelay:5.0];
}

score 1 · Accepted Answer · answered Jan 31 '15 at 11:50

Try this code, I added a incrementing delay, but I'm not sure if this is a healthy approach. Anyways, It shouldn't be a problem for small loops :

- (IBAction)testButton:(id)sender {
    NSArray *array = [NSArray arrayWithObjects:
                      @"Hefeweizen", @"IPA", @"Pilsner", @"Stout", nil];

    int64_t delayInSeconds = 5.0;

    for (NSIndexPath *anIndexPath in array)
    {

        dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);

        dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
            NSLog(@"INDEX PATH %@",anIndexPath);
        });
        delayInSeconds += 5;
    }
}

Thanks ! Exactly what I wanted. – Ramanan R R Jan 31 '15 at 12:30 — Ramanan R R, Jan 31 '15 at 12:30

Delay for all value in loop

3 Answers3