ViewDidLoad（）中的调用方法

Question

I'm calling a method on a key event which updates a label.

    [self updateFolderText];

When I do this in the event method it works, but when I try to do this in the ViewDidLoad() I get a compiler error.

- (void)viewDidLoad
{
    [super viewDidLoad];     
    [self updateFolderText];
}

I get the following error:

    error: Automatic Reference Counting Issue: Receiver type 'ViewController' 
for instance message does not declare a method with selector 'updateFolderText'

Ehm... I guess this must be trivial... I'm new to objective-c. Thanks. :)

Answer 1

The issue is probably because your method updateFolderText is defined below viewDidLoad . Move your code for updateFolderText below, and it should work.

Or, you can declare the method explicitly in your class. Add the following above @implementation .

@interface className()
-(void)yourMethod; //not sure how youve fully define updateFolderText
@end

or, as you say, you can also define it in your header file:

-(void)yourMethod; //not sure how youve fully define updateFolderText

Answer 2

You need to make sure that you have declared the function updateFolderText in the .h of teh viewcontroller before the @end usually (for public functions) or for private functions you would declare it at the top of the .m with

@interface viewcontrollername()
-(void)updateFolderText;
@end

it was probably working else where in code because you have the function itself above where it gets called

Answer 3

Make sure your method is declared in the interface for your class. There are two options for this. To declare it as a publicly accessible method for your class, you must put it in the header (.h) file.

The declaration would look something like:

@interface myClass : UIViewController
- (void)updateFolderText;
@end

To declare is as a method that is only accessible within your class (well, not really, but effectively) then you can put this at the top of your .m file, before @implementation

@interface myClass ()
- (void)updateFolderText;
@end

This second approach makes the method "private" as far as build time warnings are concerned. Note that actually the class will still respond to this selector at runtime though.

Answer 4

Make sure -(void)updateFolderText is defined, either in your .h file or in your private interface in the .m file. Also, if -(void)updateFolderText is physically located ABOVE the viewDidLoad method in your .m file, it should be able to see it ok.