setText in UIlabel after notification call has no effect

Question

i want update the text of my label every time i receive notification from nsmanageObjContext.

this is my code for add the observer:

- (IBAction)requestFotPhoto {

[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(updateLabel) name:NSManagedObjectContextDidSaveNotification
                                           object:self.facebook.managedObjectContext];

and this is the method for update the label:

-(void)updateLabel
{
        NSString *text = [NSString stringWithFormat:@"Downalad %i pictures",[Photo NumeberOfAllPhotosFromContext:self.facebook.managedObjectContext]];
        dispatch_async(dispatch_get_main_queue(), ^{
            //UIKIT method
            NSLog(@"text %@",text);
            [self.downlaodLabel setText:text];
        });
}

i assume that updateLabel is execute in a another thread, so i execute the instructions for update the label on the main thread, but this code has no effect. where is the problem?

obviously the NSlog print the right message!

thanks!

Do you see any warnings? I think you can't use variable you declared outside a block like that. — Enrico Susatyo, Oct 06 '13 at 12:36
no warning or error. in other situation i use the local variable inside a block, and all works fine — Max_Power89, Oct 06 '13 at 12:45
Unless you're doing something strange, `IBAction` methods are called on the main thread. Is `downlaodLabel` actually set to something? — Wain, Oct 06 '13 at 12:45
'downloadLabel' is a property connect with the storyboard, if i try to set the label on 'requestFotPhoto' method, the label is set correctly. — Max_Power89, Oct 06 '13 at 12:52
Are you sure it's hooked up correctly? You are spelling `download` wrong in `self.downlaodLabel`... If the NSLog statement is working, then it's a connection issue — iwasrobbed, Oct 06 '13 at 16:10
If the text is properly set when called in `IBAction` method, then it might not be a connection issue. Still, you can check if the label is not `null` before setting its text just for testing. Or maybe the text is changed to something else/original text right after that method set for the text on your label. Maybe you should lookout for that. — Zen, Oct 06 '13 at 18:43

score 0 · Answer 1 · edited May 23 '17 at 12:11

0

In your situation you don't need to use dispatch_async, because notification handlers are run in the main thread. They are executed in a main loop on idle moments — sorry if I'm wrong with techincal words, english is not native for me.

And one more thing: you should't reference self from blocks, because self points to your block, and block points to self — they're not going to be released. If you really want to do it, you can read this question.

edited May 23 '17 at 12:11

Community

1
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answered Oct 06 '13 at 18:23

Stanislav

410
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11

if i leave dispatch_async is the same! it doesn't work. maybe the problem is that method is call a lot of time, so the label dont have time to refresh itself – Max_Power89 Oct 06 '13 at 18:32
Set a breakpoint — maybe `self.downlaodLabel==nil`? It can be if your function is called before the view is layed out. You can also try `NSLog(@"%@", self.downlaodLabel.text)` right after you set a value. If you see this value — it means, that it gets changed somewhere else after this. – Stanislav Oct 06 '13 at 20:30
You can also try to wrap you method in `[self performSelector:@selector(innerUpdateLabel) withObject:nil afterDelay:0]` and see what happens – Stanislav Oct 06 '13 at 20:41
the downloadLabel is not nil. i have solved by putting the label in `requestFotPhoto` and now works correctly. but i don't know which is the original problem! – Max_Power89 Oct 06 '13 at 21:46

score 0 · Answer 2 · answered Nov 02 '21 at 09:37

seems like:

your should move your NSNotificationCenter addObserver code, from your (IBAction)requestFotPhoto (seems is some button click event handler, which only run after user tapped) to viewDidLoad

shold like this:

- (void)viewDidLoad {
    [super viewDidLoad];

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(updateLabel) name:NSManagedObjectContextDidSaveNotification object:self.facebook.managedObjectContext];
}

and for noficacation handler, not use dispatch_async

should like this:

- (void)updateLabel:(NSNotification *) notification {
    NSLog (@"updateLabel:  notification=%@", notification);
    if ([[notification name] isEqualToString: NSManagedObjectContextDidSaveNotification]) {
        NSDictionary *passedInUserInfo = notification.userInfo;
        NSString *yourText = [passedInUserInfo objectForKey:@"dataKey"];

        //UIKIT method
        NSLog(@"yourText=%@",yourText);
        [self.downlaodLabel setText:yourText];
    }
}

and somewhere else should send the text:

NSString *newText = @"someNewText";
NSDictionary *passedInfo = @{@"dataKey": newText};
[[NSNotificationCenter defaultCenter] postNotificationName:NSManagedObjectContextDidSaveNotification object: self userInfo:passedInfo];

for more detail pls refer another post answer

setText in UIlabel after notification call has no effect

2 Answers2