Xcode 8 Objective-C Category Warning

Categories in Objective-C aren't working

It really seems like your category isn't being compiled or linked into the same target that you're using it from. You should make sure that NSData+Base64.m is marked to be compiled by the same target that it's being used from by getting info on the two files and comparing the targets they're assigned to.

A test you can perform is to add a line with an #error error message to NSData+Base64.m, which will cause the build to fail when it gets to that file. Like this:

#error We're now compiling NSData+Base64.m

Then look and see which target fails to compile.

How to supress warning on the line on Objective-C compiler?

The easiest way to fix this is just to get the class a different way:

[NSClassFromString(@"UIWebDocumentView") jr_swizzleMethod:@selector(canPerformAction:withSender:) withMethod:@selector(myCanPerformAction:withSender:) error:nil]; // warning here

Suppress warning Category is implementing a method which will also be implemented by its primary class

A category allows you to add new methods to an existing class. If you want to reimplement a method that already exists in the class, you typically create a subclass instead of a category.

Apple documentation: Customizing existing classes

If the name of a method declared in a
category is the same as a method in the original class, or a method in
another category on the same class (or even a superclass), the
behavior is undefined as to which method implementation is used at
runtime.

Two methods with the exact same signature in the same class would lead to unpredictable behavior, because each caller cannot specify which implementation they want.

So, you should either use a category and provide method names that are new and unique for the class, or subclass if you want to change the behavior of an existing method in a class.

---

Related Topics