How can I programmatically dismiss a UIAlertController - ios

Question

I need to programmatically dismiss a UIAlertController that I'm using as a "please wait" message. I can present the alert without problem but when it comes to dismissing the alert, 50% of the time it dismisses and the other 50% it doesn't, forcing me to restart the app just to continue using it. Any ideas how to dismiss the alert with 100% consistency?
//loadingAlert is a UIAlertController declared in the .h file
//present the Alert
loadingAlert = [UIAlertController alertControllerWithTitle:#"Loading..." message:#"Please wait while we fetch locations" preferredStyle:UIAlertControllerStyleAlert];
[self presentViewController:loadingAlert animated:YES completion:nil];
//parse JSON file
_listOfAcquisitions = nil;
MNSHOW_NETWORK_ACTIVITY(YES);
NSString *WebServiceURL = [NSString stringWithFormat:#"JSON URL", _search];
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(queue, ^{
NSDictionary *dictionary = [JSONHelper loadJSONDataFromURL:WebServiceURL];
dispatch_async(dispatch_get_main_queue(), ^{
_listOfAcquisitions = [NSMutableArray array];
for (NSDictionary *oneEntry in dictionary) {
Acquisitions *acqu = [[Acquisitions alloc] init];
if([oneEntry objectForKey:#"ADDRESS1"] == (NSString *)[NSNull null]){acqu.ADDRESS1 = #"";}
else {acqu.ADDRESS1 = [oneEntry objectForKey:#"ADDRESS1"];}
if([oneEntry objectForKey:#"STATEABBR"] == (NSString *)[NSNull null]){acqu.STATEABBR = #"";}
else {acqu.STATEABBR = [oneEntry objectForKey:#"STATEABBR"];}
if([oneEntry objectForKey:#"TOWN"] == (NSString *)[NSNull null]){acqu.TOWN = #"";}
else {acqu.TOWN = [oneEntry objectForKey:#"TOWN"];}
if([oneEntry objectForKey:#"ZIPCODE"] == (NSString *)[NSNull null]){acqu.ZIPCODE = #"";}
else {acqu.ZIPCODE = [oneEntry objectForKey:#"ZIPCODE"];}
[_listOfAcquisitions addObject:acqu];
}
dispatch_async(dispatch_get_main_queue(), ^{
MNSHOW_NETWORK_ACTIVITY(NO);
[self refreshAnnotations:self];
});
});
});
//finally dismiss the alert...
[loadingAlert dismissViewControllerAnimated:YES completion:nil];
}

Answer 1

I've just been learning how to do this.
So, wherever the alert controller is built, you need to add the action button either to "OK" in default style or "Cancel" in cancel style.
UIAlertController *alertController = [UIAlertController
alertControllerWithTitle:#"You made a mistake."
message:#"Pray we don't alter the alert further"
preferredStyle:UIAlertControllerStyleAlert];
UIAlertAction *okayAction = [UIAlertAction
actionWithTitle:#"OK"
style:UIAlertActionStyleDefault
handler:^(UIAlertAction * _Nonnull action) {
[alertController dismissViewControllerAnimated:YES completion:nil];
}];
[alertController addAction:okayAction];
[self presentViewController:alertController animated:YES completion:nil];
There are other UIAlertActionStyle enumerations, such as UIAlertActionStyleCancel which will put a separator space between other actions and UIAlertActionStyleDestructive which will make the font red but will be in line with other UIAlertActions.
Make sure you add in order: standard actions (Okay, Open Camera, Photo Library) and THEN cancel actions.
There's also preferredStyle:UIAlertControllerStyleActionSheet which is used to set up options for the user. I use this to show Camera and Photo Library.
Also, for your specific dismiss action. The reason it's not working is because you are attempting to dismiss it on the background thread. You should ALWAYS dismiss or make UI changes on the foreground thread. This will cause an NSException/crash in the future.
dispatch_async(dispatch_get_main_queue(), ^{
// dismiss your UIAlertController
});
This is how you should be doing it with your specific code:
dispatch_async(dispatch_get_main_queue(), ^{
MNSHOW_NETWORK_ACTIVITY(NO);
[self refreshAnnotations:self];
[loadingAlert dismissViewControllerAnimated:YES completion:nil];
});
});
You have other issues with your code that you should ask others for help about. I am only a junior developer so I'm not sure how to correctly do what you're trying to do but this should help with dismissing.
You might want to look into loading wheels or toast messages that will say "Please wait" or "Loading".
Using a UIAlertController to show a loading message is rather bad taste.

Answer 2

First of all your network call should probably happen in the completion block of the presentViewController. So you don't dismiss it before it has appeared.
Also the nested dispatch_async seems off, since you call dispatch_get_main_queue(line 32) while already within the mainQue(line 13). And if this were to work the dismiss would need to be within the dispatch_async block so that it actually would dismiss.
But more importantly this is kind of a misuse of the UIAlertController API. Those are intended for user input not to Block UI.
You are better of implementing your own custom view subclass.
Or using MBProgressHUD (https://github.com/jdg/MBProgressHUD). There you can use either the MBProgressHUDModeIndeterminate or MBProgressHUDModeText to accomplish what you are trying.

Answer 3

You're creating/starting/dismissing the alert all within the same block, which means both presentViewController:loadingAlert and [loadingAlert dismissViewControllerAnimated: are being called in the same runloop. This is why you're getting unexpected results.
The dismiss needs to be called from a different cycle of the runloop, so having it called in a separate *block is what you want. You're already doing things in different threads using dispatch_async, which execute in discretely separate runloop so the solution for you is to put the dismissViewControllerAnimated: call within the dispatch_async(dispatch_get_main_queue() to ensure that its both called on the main thread for UI updates, and called in a separate run-loop as its presentation.

Answer 4

You could use dismissWithClickedButtonIndex:animated: but it's now deprecated in iOS9. I would use a timer:
// 3 second delay
[NSTimer scheduledTimerWithTimeInterval:3 target:self selector:#selector(dismissAlert) userInfo:nil repeats:NO];
- (void) dismissAlert {
[loadingAlert dismissWithClickedButtonIndex:0 animated:YES];
}
Of course, this isn't what UIAlertViews are intended for. You'd be better of using a loading spinner somewhere (UIActivityIndicatorView).