calling function problem (iphone)

Question

From class picViewController i am calling function imageCliked on scrollViewController in order to fire function loadPage but it does work. Compiler error:

"Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** +[scrollViewController loadpage:]: unrecognized selector sent to class 0x17198'"

Anybody can help?

@interface scrollViewController : UIViewController <UIScrollViewDelegate> {
}
- (void)loadPage:(int)page;  // loads a new picViewController
+(void) imageCliked;
@end

#import "scrollViewController.h"
#import "picViewController.h"
#import "MLUtils.h"

@implementation scrollViewController

- (void)loadPage:(int)page {
// I need to call this function from +(void) imageCliked 
}
/* this function is called by picViewController pressButton1 */

+(void) imageCliked {
NSLog(@"left");
[self loadPage:3];// does not work
}
@end





#import "picViewController.h"
#import "scrollViewController.h"

@implementation picViewController

- (void) pressButton1:(id)sender{
 [scrollViewController imageCliked];

}

@end

Answer 1

You have a mismatch between class methods and instance methods. Methods that start with + belong to the class, and ones that start with - belong to the instance.

The specific error you see above happens because you're trying to call an instance method (-loadPage) from a class method (+imageClicked), which doesn't work-- "self" inside of imageClicked refers to the whole class, so that's why it fails.

My guess is that you actually want both of those methods to be instance methods. Make them both prefixed with -.

But it sounds like you might need to review some basics in the first couple chapters of Apple's Objective-C documentation.

Answer 2

If it is a class, please name it starting with a capital letter.

---

[self loadPage:3];

Since self is a class in +imageCliked, the loadPage: method must be a class method as well. But you're declaring -loadPage: as an instance method. The two are not exchangeable. Either

1. Make +loadPage: a class method (change the - to +), or
2. Create a temporary instance of scrollViewController, i.e. [[[[self alloc] init] autorelease] loadPage:3];, or
3. Make -imageCliked an instance method, and create an instance in -pressButton1:.