问题
I am getting odd behavior from an NSAlert in two different parts of my program. The behavior is:
- Alert appears and then spontaneously disappears.
- Alert reappears and then remains until dismissed by user i.e. normal behavior.
- Alert reappears again.
This behavior only occurs the first time the method that displays the alert is called. After that first time, it behaves normally.
Here is the code for the one of the parts in which the behavior occurs:
UIAlertView * locationAlert = [[UIAlertView alloc] initWithTitle:@"You are in the right place." message:nil delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
[locationAlert show];
[locationAlert release];
Or if you prefer, with a bit more context:
- (IBAction)locateMe {
NSLog(@"About to check location");
locMan = [[CLLocationManager alloc] init];
locMan.delegate = self;
locMan.desiredAccuracy = kCLLocationAccuracyThreeKilometers;
locMan.distanceFilter = 1609; //1 mile
[locMan startUpdatingLocation];
}
- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation * )oldLocation {
if (newLocation.horizontalAccuracy >= 0) {
CLLocation *airportLocation = [[[CLLocation alloc] initWithLatitude:51.500148 longitude:-0.204669] autorelease];
CLLocationDistance delta = [airportLocation getDistanceFrom: newLocation];
long miles = (delta * 0.000621371) + 0.5; //metres to rounded mile
if (miles < 3) {
UIAlertView * locationAlert = [[UIAlertView alloc] initWithTitle:@"You are in the right place." message:nil delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
[locationAlert show];
[locationAlert release];
[locMan stopUpdatingLocation];
} else {
UIAlertView * locationAlert = [[UIAlertView alloc] initWithTitle:@"You are not in the right place." message:nil delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
[locationAlert show];
[locationAlert release];
[locMan stopUpdatingLocation];
}
}
}
- (void) locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error {
UIAlertView * locationAlert = [[UIAlertView alloc] initWithTitle:@"Error." message:error.code delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
[locationAlert show];
[locMan release];
locMan = nil;
}
Any ideas? Thanks.
Edit---------
The other place this happens is:
- (void)parser:(NSXMLParser *)parser parseErrorOccurred:(NSError *)parseError {
NSString * errorString = [NSString stringWithFormat:@"Unable to download feed from web site (Error code %i )", [parseError code]];
NSLog(@"error parsing XML: %@", errorString);
UIAlertView * errorAlert = [[UIAlertView alloc] initWithTitle:@"Error loading content" message:errorString delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
[errorAlert show];
}
For context the first case is in the AppDelegate and the second in the view controller for the 1st tab view. The second problem occurs every time the xml is reloaded when there is no internet connection. The first one only occurs the first time the function is called.
Edit-----
If I move the alert it works. Unfortunatly this is not where I want it!
- (IBAction)locateMe {
UIAlertView * locationAlert = [[UIAlertView alloc] initWithTitle:@"You are in the right place." message:nil delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
[locationAlert show];
/*
NSLog(@"About to check location");
locMan = [[CLLocationManager alloc] init];
locMan.delegate = self;
locMan.desiredAccuracy = kCLLocationAccuracyThreeKilometers;
locMan.distanceFilter = 1609; //1 mile
[locMan startUpdatingLocation];*/
}
Update:
I set some NSLog entries and discovered that despite the addition of [locMan stopUpdatingLocation] the didUpdateToLocation function was running multiple times.
I guess the spontaneous disappearance happens because the alert view is called again and the programme clears the first instance to make way for the second automatically.
Any ideas as to why [locMan stopUpdatingLocation] doesn't work would be appreciated but in the mean time I just moved the declaration of the locationAlert out of the function (so it is global), set it in the initial locate me function and use the following the first time it is called:
[locationAlert show];
locationAlert = nil;
That way it works perfectly.
回答1:
I think the NSAlert disappearing on its own is the key to solving this.
It's simple to explain why an alert displays unexpectedly i.e. it's just been called unexpectedly. However, it's not so common to programmatically dismiss an alert. Whatever is causing it to disappear is most likely triggering the display again.
To debug I suggest:
(1) Looking in your code for the NSAlert – dismissWithClickedButtonIndex:animated: method and see if somehow you're actually dismissing the alert programmatically.
(2) I believe (someone double-check me on this) that an alert view is added as a subview to whichever base view is currently on screen. It might be that the base view is disappearing for some reason and taking the alert view with it. If the view disappears and then reappears rapidly enough, it might not be obvious when the alert is frontmost. (Edit: see Ed Marty's comment below.)
(3) Since this happens in two separate pieces of the app, compare both to find a common element or structure. That common element might be the cause. An odd problem.
Edit01: Updated for additional info
If locMan isan instance variable, it should be defined as a property and you should access it every time withself.locMan By accessing it directly, you lose your automatic retention management.
回答2:
You're not turning off your location manager when you first show the alert. As the location is refined by the device (ie, the accuracy is increased), your callback will be (potentially) called multiple times. You should use [locMan stopUpdatingLocation] after your alert display.
回答3:
I set some NSLog entries and discovered that despite the addition of [locMan stopUpdatingLocation] the didUpdateToLocation function was running multiple times.
I guess the spontaneous disappearance happens because the alert view is called again and the programme clears the first instance to make way for the second automatically.
Any ideas as to why [locMan stopUpdatingLocation] doesn't work would be appreciated but in the mean time I just moved the declaration of the locationAlert out of the function (so it is global), set it in the initial locate me function and use the following the first time it is called:
[locationAlert show];
locationAlert = nil;
That way it works perfectly.
回答4:
I encountered the same exact issue with the alert dialog appearing momentarily, reappearing, and finally appearing again after being dismissed. I was making a string comparison before deciding to show the alert view:
- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string {
if([string isEqualToString:@"OK"]) {
NSLog(@"(Settings)Registration Successful");
statusField.text = @"Registration successful!";
[settingsActivity stopAnimating];
}
else {
NSLog(@"(Settings)Registration Failure");
[settingsActivity stopAnimating];
UIAlertView * regFail = [[[UIAlertView alloc] initWithTitle:@"Registration Error!" message:@"Please check your email address and try again." delegate:self cancelButtonTitle:@"OK" otherButtonTitles: nil] autorelease];
[regFail show];
}}
To correct this behavior I simply verified the returned string rather than just showing the alert:
- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string {
if([string isEqualToString:@"OK"]) {
NSLog(@"(Settings)Registration Successful");
statusField.text = @"Registration successful!";
[settingsActivity stopAnimating];
}
else if([string isEqualToString:@"Error"]) {
NSLog(@"(Settings)Registration Failure");
[settingsActivity stopAnimating];
UIAlertView * regFail = [[[UIAlertView alloc] initWithTitle:@"Registration Error!" message:@"Please check your email address and try again." delegate:self cancelButtonTitle:@"OK" otherButtonTitles: nil] autorelease];
[regFail show];
}
回答5:
I also got the Same problem while working on Location Manager. Here i checked with Nslog but it is executing multiple times, finally i fount that i am creating multiple objects and using Sharedinstance for same ViewController that contains Location Manger but i am not releasing the object, so at perticular location how many objects if we create that many times the location detects.So while working on LocationManger check handling objects thoroughly to reduce these type of problems.
来源：https://stackoverflow.com/questions/2273283/uialertview-pops-up-three-times-per-call-instead-of-just-once