I am not able to find out why am I getting unnecessary warnings like:
"Method 'someMethod' not found"? Though at run time it is executing this method and I am getting the desired results. FYI... The called method resides in separate class which i have already imported in my class.
Usually one of two reasons:
1) You haven't casted the object that you're calling that method on correctly.
[(UITableView*)myTableView setDelegate:self];
2) The method that you're calling may not be in your custom Class' (public) #interface
#interface MyCustomClass : NSObject {
}
- (void)doSomethingReallyImportant;
#end
If you are trying to do something to an object, did you cast your object to the object's class?
If you are trying to access a method in your implementation of a class, do you have that method declared in your .h?
Then you have probably not put that method in the class' #interface. You should if it is a public method.
Being able to compile without warnings is a good thing.
Related
Say we have parent class
ParentViewController.h
#interface ParentViewController
....
#end
ParentViewController.m
#interface ParentViewController()
- (NSArray *)selectedItems;
#end
#implementation ParentViewController
.....
#end
And then we subclass it
ChildViewController.h
#interface ChildViewController : ParentViewController
....
#end
ChildClassViewController.m
#implementation ChildViewController
- (void)doSomething
{
// XCode Warning Flag on this line
NSUInteger count = [self selectedItems];
.....
}
XCode will set Warning flag at the commented line and says that "Instance method '-selectedItems' not found (return type defaults to 'id').
Yes I know that in ObjC there is no such thing as private methods, but using an empty category kind of gives the ability to do so. But somehow it does not get inherited by subclasses.
I usually fix it by moving the method from ParentViewController.m to ParentViewController.h. This feels weird, I loose the ability to make the method private just because I need to subclass it.
Now my question is:
Why does the parent subclass cannot find those methods that is declared in its category at the .m file?
Is there a way to remove the Warning Flag but without losing the ability to keep the method private.
Hopefully someone with more experience will be able to help explain this annoying issue.
First, note that your "empty category" isn't a Category at all, it's a Class Extension. Class Extensions very similar to categories but they're new in Objective C 2.0, and they differ slightly in their use. Primarily, the compiler will warn you if you don't implement a method in a Class Extension, but it won't with a Category. Anyways, on to the issue at hand...
Privacy in Objective-C is all about visibility. If the compiler can't see see the declaration of a method that's being used, you'll get a warning. Note that if you were to implement your subclass in the same file as your Class Extension, the compiler won't warn you because it can see the declaration.
Therefore, If you want to use "private" methods in subclasses, you just need some way of showing the compiler that those methods exist. My favorite pattern is to declare the private methods in a Category in a separate file (like MyClass_private.h). You then only import that interface into the implementation files of the base class and any derived classes that need to see it.
I have a solution, but generally I would advise against it. if you compile the file with -w (suppress all warnings), the warning goes away. I do not know if there is a specific warning flag for this message, if there was, you could use #pragma GCC diagnostic ignored "-Winstance-method-not-found", but I can't find it, sorry.
what does it mean to create a category like this: #interface myClass () ... #end in the same class's .m file ? this category may contain methods and properties, why not to add these methods and properties directly in the class's .h file ?
thank you in advance.
It's basically a workaround for Objective-C's lack of private methods. You put classes in there to hide them from users of the class. They can technically still use them (although they'll get a warning) but if they don't know about them, they probably won't.
Sometimes i would do this when i had a private method.
Because,if the method not define in header,when you call it in implementation,you got a warning, (your method's code is above your invoked).
like this:Instance method '-XXX' not found (return type defaults to 'id')
So,for no warning,i put a method define in a category maybe i will write a #interface myClass(private).
If there is no name in the parenthesis it is a class extension. If you define a name then it is a category.
The most common reason to do this is to hide instance variables and methods. To make the appear to be private.
Simple question, as I am coming from another programming language. In Objective-C, lets say in a controller class I want to separate certain code into its own method, how do I call that method let's say, from viewLoad. As an example, let's say I create a method:
(void)checkIfInputCorrect
{
NSLog(#"text");
}
Now, i wanted to have in a delegate method, call this method. I tried [self checkIfInputCorrect] and get a warning saying Controller may not respond to -CheckIf...
I thought something like checkIfInputCorrect() would work that gives an error as well.
Basically how do you call a method?
Add this to your .h file
- (void)checkIfInputCorrect;
Call it with:
[self checkIfInputCorrect];
You need to list the method in the interface (ideal) or list the method implementation before the calling method (less ideal) so that the compiler can know that the class responds to the selector before it compiles the calling line.
To paraphrase Martin,
In your .m file, make sure your method -checkIfInputCorrect is placed so that it's physically above the method that has the line: [self checkIfInputCorrect];
This could be me doing the design pattern wrong.
I'm implementing asynchronous delegation in an application that uses NSURLConnection. An object wraps the NSURLConnection and handles its delegated messages; that works fine. Now I'm defining my own delegates in the object that uses it (NSURLConnection messages ConnectionWrapper, ConnectionWrapper messages NeedsToUseConnection, you get the idea), and that works as well, however, Xcode emits this warning:
No '-request:finishedWithResult' method found
This is, presumably, because I'm declaring the delegate I'm calling like this:
id<NSObject> delegate;
...and Xcode is checking what NSObject declares in the Foundation framework. My custom delegate message is not there. I am properly insulating the call:
if([delegate respondsToSelector:#selector(request:finishedWithResult:)])
[delegate request:self finishedWithResult:ret];
Aside from turning the warning off -- I like to work with as many warnings on as possible -- is there a way to communicate (either syntactically or via a compiler directive) that I am aware this message is undeclared? Should I, instead, be using an interface design pattern for this รก la Java? Using id<WillReceiveRequestMessages> or something?
Open to suggestion.
A better way of doing it would be to create your own delegate protocol:
#protocol MyControlDelegate <NSObject>
#optional
- (void)request:(MyControl *)request didFinishWithResult:(id)result;
#end
Then, you would declare your delegate like this:
id <MyControlDelegate> delegate;
The compiler will no longer complain when you write this:
if ([delegate respondsToSelector:#selector(request:didFinishWithResult:)])
[delegate request:self didFinishWithResult:result];
The <NSObject> syntax is important in the protocol definition because it tells the compiler to incorporate the NSObject protocol. This is how your protocol gets methods like respondsToSelector:. If you left that out, the compiler would start complaining about respondsToSelector: instead.
This is, presumably, because I'm declaring the delegate I'm calling
like this: ...and Xcode is checking what NSObject declares in the
Foundation framework.
That is incorrect. If that were the case then you would get a warning about the object "may not respond to" the method, or something like that. This is a completely separate problem.
This warning is due to the fact that the compiler must know the signature of a selector in order to call it. This is because, behind the scenes, the compiler translates a method call to either objc_msgSend or objc_msgSend_stret depending on whether the method returns a struct type or not. If it doesn't know the return type, it will guess that it is not a struct, and use the first function. However, this could be wrong.
The solution is to have the method declared anywhere at all. It doesn't even have to be declared in the right class. You can declare it in some dummy protocol that is never used. So long as it is declared somewhere, the compiler will know and will be able to correctly compile it.
I write an instance method in ClassName.m:
-(void)methodName:(paraType)parameter
{...}
And call it using [self methodName:parameter]; A warning will pop up, but the code still runs successfully.
Is this because I haven't created an instance of the class? Why the method still runs normally? And what is the correct way to call self method to prevent the warning?
Well the first step in receiving help with a warning would be to post the warning :)
I am assuming it is something about an unrecognized message? If so it's because although the compiler sees the call to "methodName" it does not know if that is valid for the object or not.
I would guess your code looks like;
-(void) someFunc
{
...
[self methodName:parameter];
...
}
-(void)methodName:(paraType)parameter
{
...
}
You can either;
a) Place the 'methodName' function earlier in the file so the compiler has seen it before it's used in calls.
b) declare it in the class interface. E.g.
// Foo.h
#interface Foo {
...
}
-(void) methodName:(paraType)parameter;
#end
What is the warning that you get?
Do you have a definition of the method in your header file?
The syntax you use is the propper way of calling method on self.
The method will work because Objective-C methods are resolved at run-time. I expect the warning you get is something like "Object Foo may not respond to -methodName:" and then it tells you that it's defaulting the return type to id. That's because the compiler hasn't seen a declaration or definition of -methodName: by the time it compiles the code where you call it. To remove the warning, declare the method in either the class's interface or a category on the class.
If you are getting a warning it might be because the method signature isn't in an interface.
#interface foo ....
-(void)method;
Once the implementation is written the warning should go away since it's not the first time the compiler has seen the method. It will work without doing this, but the warning message is annoying.