CODEWITHSUNDEEP
iphonexcodemethodscall
Zachary Webert
Zachary Webert

Reputation: 21

Why is xcode giving me a "method not found" error?

I have an object called Shot which is a subclass of UIIMageView.

//  Shot.h

#import <Foundation/Foundation.h>


@interface Shot : UIImageView {
    CGPoint position; 
}
- (void)SetShot:(CGPoint *)point;
@end


//  Shot.m


#import "Shot.h"


@implementation Shot

- (void)SetShot:(CGPoint *)point;
{
    position.x = point->x;
    position.y = point->y;

}

@end

When I try to call the SetShot method, xcode gives me this warning:

method -SetShot not found(return type defaults to id)

Here is the call:

//CustomImageView.m
#import "CustomImageView.h"

@class Shot;
@implementation CustomImageView

-(id) initWithCoder:(NSCoder *)aDecoder
{
    self.userInteractionEnabled = YES;
    return self;
}


-(void) setInteraction
{
    self.userInteractionEnabled = YES;
}


- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [touches anyObject];
    CGPoint point = [touch locationInView:self];
    Shot *shot;

    [shot SetShot:point];

}

- (void)dealloc
{
    [super dealloc];
}
@end

When I run the program, I get a fatal error when the method is called. Why is that?

Upvotes: 0

Views: 3621

Answers (3)

user557219
user557219

Reputation:

There are three problems in your code. Firstly, you need to import Shot.h in your CustomImageView.m implementation file:

#import "Shot.h"

instead of simply forward-declaring the Shot class:

@class Shot;

When the compiler sees a forward declaration, it becomes aware of the existence of that class but doesn’t yet know its attributes, declared properties, or methods — in particular, it doesn’t know that Shot has a -SetPoint: instance method.

Secondly, you’re not creating an instance of Shot:

Shot *shot;
[shot SetShot:point];

This only declares that shot is a pointer to Shot but there’s no allocation/initialisation. You should create an object, i.e.:

Shot *shot = [[Shot alloc] init];

then use it:

[shot SetShot:point];

and, when you don’t need it any longer, release it:

[shot release];

Although it’s not clear what’s the benefit of creating a shot, setting its point, and then releasing it. Unless your code is a contrived example, you might want to rethink this behaviour.

Also, your -SetPoint: method has a pointer to CGPoint parameter but you’re passing a CGPoint value (i.e., not a pointer) argument:

// point is not a pointer!
CGPoint point = [touch locationInView:self];
Shot *shot;
[shot SetShot:point];

I suggest you drop the pointer altogether, i.e.:

- (void)SetShot:(CGPoint)point;
{
    position = point;    
}

and maybe use a declared property instead of a manually implemented setter method.

Upvotes: 5

PengOne
PengOne

Reputation: 48398

You have not created an instance of Shot; you have only created a pointer with:

Shot *shot;

You must allocate and initialize it:

Shot *shot = [[Shot alloc] init];

At some point you must import the header file Shot.h as well.

Upvotes: 1

Dair
Dair

Reputation: 16240

Do

#import "Shot.h"

instead of:

@class Shot;

Upvotes: 3

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