Question

I read alot about what is the problem for exception “unrecog…” But i need something else

I have view with two buttons: Start and Delete, also i have two UILabels: oneLabel and secondLabel

So the I press button Start I start NSOperation thread started

And I give him labels (oneLabel,secondLabel) as params

to change text of labels on main loop i use

[oneLabel performSelectorOnMainThread:@selector(setText:) withObject:someString waitUntilDone:YES];

All works fine, but when i press button Delete – it’s deleting secondLabel from view with method

[secondLabel removeFromSuperview] 

and then

secondLabel=nil;

So, after what i get exception. I understand why it happened – because the target object for message with selector setText if not available now becaus it’s nil.

And i get exception and app crashes.

How i can Catch this exception in this case?

For what i need it for? When use tableView controller with ImageView wich loads images in separate thread.

Answer 1

try this:

id yourObject;
    if (yourObject != nil && [yourObject respondsToSelector:@selector(yourSelector)]) {
    // Do your stuff here
}

This will only call your method to be executed if your objects is still available and it responds to the specifed selector.

Hope this helps, Vlad