如何修复此警告：“找不到方法（返回类型默认为'id'）”

Question

I am trying to get rid of some of these warnings from my iPhone application. The one I get the most is when I have a void function and I call it using [self myFunction];. The warning is on the line where I call the function and it says: "Method '-myFunction' not found (return type defaults to 'id')." What do I need to do to fix this? Thanks

Answer 1

Declare the function in your header file, like so:

 -(void)myFunction;

or

 -(NSString*)myFunction;
 -(id)myFunction;
 -(NSInteger)myFunction;
 -(BOOL)myFunction;

etc etc.

This is of more importance than just silencing the compiler: if the return type of a function is not a pointer ( id or anything* ), especially when it doesn't have the same size, you can get really odd and hard to find bugs.

Eg if a function returns a CGRect struct, and the compiler assumes id (as the warning says), really weird things will happen.

Answer 2

You need to define that function in your header file (.h) (if it should be visible to other classes), or in your implementation file (.m) if it is private to your class.

For example, if you use a method:

-(void)myFunction {
    // do something
}

For a "private" function, add this at the top of your .m file; before the @implementation MyCoolClass line.

@interface MyCoolClass()  // <--- no 'category name' hides methods just for this file
-(void)myFunction;     // <--- add the method here
-(void)myOtherFunction;
-(void)doSomeCoolThingWithThisString:(NSString *)firstName;
@end

OR if you want to call the method from other files, add it in your .h file, inside the 'interface' section; after all your properties, and before the @end.

Good luck!

Answer 3

您需要导入包含您的方法的.h文件

Answer 4

I decide this problem next:

--file: MyObjectController.h--

#import "MyObject.h"

@interface MyObjectController
{
    MyObject * obj;
}
-(void) makeSomething;

@end

--file: MyObjectController.mm--

#import "MyObjectController.h"

@implementation MyObjectController

-(void) makeSomething {}

@end

---file MyObject.h ----

@class MyObjectController;

@interface MyObject
{
    MyObjectController * objController;
}
-(void) callMakeSomethingFromObjController;

@end

---file MyObject.mm ----

#import "MyObject.h"  
#import "MyObjectController.h" //Add this line!!! And compiller will found makeSomething    

@implementation MyObject

-(void) callMakeSomethingFromObjController
{
     [objController makeSomething];//warning was here:instance method '-makeSomething' not found (return type defaults to 'id')  
}

@end

Answer 5

Ensure you have -(void) myFunction; declared in your header file and ALSO ensure that myFunction doesn't return anything.

Answer 6

Just make sure the function is placed before the caller in your .m file!! I don't whether this is the correct way to do things but it does removed all those warning for me.

And in apple's sample code, I don't see they declare all methods in the h or m file. Can just use it straight away.

Answer 7

I had a similar issue pop up for me and it was because I had another header file with the same name in a different sub-directory within the project that I thought I had deleted. This was ultimately making the compiler think the method was not declared in the header because it was looking in the wrong header file.

Answer 8

Make sure that the object you're using has this function declared also in its header file.

sky.h :

@interface sky : object {

}

-(void) doSomething:(int)param;

@end

sky.m :

#import "sky.h"
@implementation sky

-(void) doSomething:(int)param

{

    //dosomething usefull 
}