Objective C - 来自另一个类的Call方法

Question

I have 2 classes geoViewController and geoMainViewController

I have a method in the geoMainViewController called getFoo

It looks like this:

- (NSString *)getFoo
{

NSString* foo = @"This is foo";

return foo;

}

I am trying to call getFoo from the geoViewController class.

I have #import "geoMainViewController.h" in my geoViewController m file.

I am trying instantiate the geoMainViewController class and call the getFoo method from the viewDidLoad in my geoViewController class like this:

- (void)viewDidLoad
{
    [super viewDidLoad];

    geoMainViewController* mainVC = [[geoMainViewController alloc] init];

    NSString* myFoo = [mainVC getFoo];    

}

It seems to be instantiating the geoMainViewController class fine but I am getting an error on NSString* myFoo = [mainVC getFoo];

The error is - no visible @interface for 'geoMainViewController' declares the selector 'getFoo'

I am sure I am missing a step because I am very new to Objective C. I am just not sure what I am doing wrong.

Any help on this would be great.

Thanks!

Answer 1

在geoMainViewController.h您应该声明选择器是可见的：

-(NSString *)getFoo;

Answer 2

Did you put - (NSString *)getFoo in your geoMainViewController.h ? You have to make those methods visible to the outside of your object through the .h file, so other objects know which selectors they respond to. Did the autoComplete fill in the message per chance?

#import <Foundation/Foundation.h>

@interface 
{

}

@property (nonatomic,strong) ;
@property (nonatomic,strong) ;
@property (nonatomic, strong) ;

- (NSString *)getFoo
@end

EDIT: (You could also just make Foo a property by the way)

Answer 3

Did you declare it in your header file?

Header file contains all the function declarations in the .h file and you only include the .h file in your class. So it depends on .h file. .h file will have all the functions as the .m file.

Hope it helps you.

Answer 4

You are misunderstanding how to use a view controller. While you can technically create an instance of a view controller in order to call one of its methods, you shouldn't do so. The normal approach is that the view controller is part of the view hierarchy and you can call methods on it when you have access to that instance. You are missing something fundamental here.

Your actual error is a missinh method declaration, I would suspect, but you have bigger problems to solve first.