Categories provide the ability to add some extra functionality to an object without subclassing or changing the actual object.

For example we want to set some custom fonts. Lets create a category that add functionality to UIFont class. Open your Xcode project, click on File -> New -> File and choose Objective-C file , click Next enter your category name say "CustomFont" choose file type as Category and Class as UIFont then Click "Next" followed by "Create."

Declare the Category Method :-

Click "UIFont+CustomFonts.h" to view the new category's header file. Add the following code to the interface to declare the method.

@interface UIFont (CustomFonts)

+(UIFont *)productSansRegularFontWithSize:(CGFloat)size;

@end

Now Implement the Category Method:-

Click "UIFont+CustomFonts.m" to view the category's implementation file. Add the following code to create a method that will set ProductSansRegular Font.

+(UIFont *)productSansRegularFontWithSize:(CGFloat)size{
    
    return [UIFont fontWithName:@"ProductSans-Regular" size:size];
    
}

Import your category

#import "UIFont+CustomFonts.h"

Now set the Label font

[self.label setFont:[UIFont productSansRegularFontWithSize:16.0]];