Question

Actually ,I’ve been looking around at how to call a method from a block.
I am trying to fetch all images from iphone photo app .Here is the code….

void (^assetGroupEnumerator)(ALAssetsGroup *, BOOL *) = ^(ALAssetsGroup *group, BOOL *stop)   
     if(group != nil) {
        [self.groups addObject:group];
        [group enumerateAssetsUsingBlock:selectionBlock];
    }
};

[library enumerateGroupsWithTypes:groupTypes
                  usingBlock:assetGroupEnumerator
                failureBlock:^(NSError *error) {NSLog(@"A problem occurred");}];

In selectionBlock … I just want to add an action when user click on any image.
so I tried this code ..

[imgView addTarget:self action:@selector(buttonPressed) forControlEvents:UIControlEventTouchUpInside];

buttonPressed is also defined in the same .m file.

- (void) buttonPressed: (id) sender {
UIAlertView* av = [[UIAlertView alloc] initWithTitle:@"Howdy!"
                                             message:@"You tapped me."
                                            delegate:nil
                                   cancelButtonTitle:@"Cool"
                                   otherButtonTitles:nil];
[av show];
}

But in selectionBlock I am getting “No visible @interface for ‘UIImageView’ declares the selector ‘addTarget:action:forControlEvents’ “

I am new to iOS programming. so any help would be very, very appreciated!

Answer 1

-addTarget:action:forControlEvents: is a method on UIControl. UIButton, UISwitch, and so on are all subclasses of UIControl. UIImageView, however, is not, so it does not respond to that selector. Since your imgView variable is a UIImageView, the compiler won’t let you call this method on it. This has nothing to do with calling it in from a block, btw – but only with what methods objects declare they respond to.

Hope this helps!