Do action after foreach and dispatch - ios

Question

I am trying to do an action AFTER the foreach and my dispatches. In the for loop when i come across one type of enum, the showAlert will get YES. For showing the allert after all the tasks and loops.
I've tried it, but the allert show up already when the dispatch_sync is still going. How can i solve this problem?
EDIT:
Problem overview: The problem is then that the UIAlertView already comes up before the loops are done, so i don't have any value set (For loop does this of my randomInt) and my AlertView takes this int. So That's why i want to wait until all loops/foreach are done in the method and then let the UIAlertView come up, so i have 100% the integer that i needed.
Code:
-(void)animateRolling{
[[self firstLabelOutlet] setHidden:YES];
long index;
int randomIndex;
__block BOOL showAllert = NO;
randomIndex = arc4random() % 20;
if (randomIndex == 8) {
[self showAd];
}
for(detailDice* cell in [[self dobbelstenenCollection] visibleCells]){
NSIndexPath *indexPath = [[self dobbelstenenCollection] indexPathForCell:cell];
if ([arrayDobbel count] >= 3) {
index = 2 * indexPath.section + indexPath.row;
}else{
index = 1 * indexPath.section + indexPath.row;
}
if ([cell isHidden]) {
[cell setHidden:NO];
}
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
for (int i = 0; i <= 10; i++) {
dispatch_sync(dispatch_get_main_queue(), ^{
if ([[arrayDobbel objectAtIndex:index] diceSoort] == ENUMHoelangDobbel) {
randomInt = ((arc4random() % ([self maxduration] - 1 + 1 )) + 1.0);
[[cell detaildiceLabel] setText:[NSString stringWithFormat:#"Seconds \n %i", (int)randomInt]];
showAllert = YES;
}else if ([[arrayDobbel objectAtIndex:index] diceSoort] == ENUMOgen){
[[cell detailDiceImage] setImage:[UIImage imageNamed:[NSString stringWithFormat:#"%i.png", ( (arc4random() % (6-1+1)) + 1 )]]];
}else{
[[cell detaildiceLabel] setText: [[arrayDobbel objectAtIndex:index] returnRandomOptie]];
}
});
[NSThread sleepForTimeInterval:0.05];
}
});
}
if (showAllert) {
[self showDurationAlert];
}
}
Kind Regards!

Answer 1

Create group with dispatch_group_create.
Use dispatch_group_async instead dispatch_async.
And path yours block, that should be performed after foreach and dispatch in dispatch_group_notify.
All is simple.

Answer 2

I would suggest to refactor your code through making animateRolling an asynchronous method, and the invocation of showDurationAlert a "continuation":
typedef void (^completion_t)(BOOL showAlert);
-(void)animateRollingWithCompletion:(completion_t)completion;
and use it as follows:
[self animateRollingWithCompletion:^(BOOL showAlert){
if (showAlert) {
dispatch_async(dispatch_get_main_queue(), ^{
[self showDurationAlert];
});
}
}];
I would also suggest to utilize a NSTimer or better a dispatch timer (dispatch_source_t) to implement the method animateRollingWithCompletion.
You can create and use dispatch timer as follows:
// Create a timer:
dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
// Define the handler block:
dispatch_source_set_event_handler(timer, ^{
...
});
// Start the timer (here, as a one shot timer):
uint64_t leeway = 0; // allowed maximum delay
uint64_t interval = delay_in_secs * NSEC_PER_SEC;
dispatch_source_set_timer(
timer,
dispatch_time(DISPATCH_TIME_NOW, interval), // time *when* to start
DISPATCH_TIME_FOREVER, // interval, DISPATCH_TIME_FOREVER for "one shot"
leeway // maximum allowed delay
);
dispatch_resume(timer);
// Cancel a timer:
dispatch_source_cancel(timer);
In order to start a periodic timer whose handler will be called at the start of each period, you might write:
dispatch_source_set_timer(
timer,
dispatch_time(DISPATCH_TIME_NOW, 0),
interval,
leeway);
dispatch_resume(timer);
With this knowledge, I think it's possible to craft a handler block, which is driven by a periodic timer. The block retrieves parameters form an array and executes your core methods (e.g. setting up the cells) on the main thread.
When all parameters have been retrieved and the work has been finished, the block may call dispatch_after() with the specified interval (or test for the "finished" condition at the start of a new period) which eventually calls the completion block provided as parameter in method animateRollingWithCompletion and defined by the call-site (which in turn brings up the Alert View).