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What is the difference between "+" and "-" before the function name interface declaration in an Objective-C program. Example:
- (void)continueSpeaking; + (NSArray *)availableVoices; What's the difference?
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One way to describe the difference is that - methods operate on objects, while + methods operate on the class itself.
With the class based function, you just call directly, but you don't have access to any local variables besides #defines that you can do because the class isn't instantiated. But with the - (NSString you must instantiate the class before use, and you have access to all local variables.
In Objective-C, any character , numeric or boolean literal prefixed with the '@' character will evaluate to a pointer to an NSNumber object (In this case), initialized with that value. C's type suffixes may be used to control the size of numeric literals. '@' is used a lot in the objective-C world.
+ defines a class method
Class methods belong to the class itself, not instances of the class.
Example: [AppDelegate someMethod]
- defines an instance method
Example [[[UIApplication sharedApplication] delegate] someMethod]
One way to describe the difference is that - methods operate on objects, while + methods operate on the class itself.
Say your class was named MyClass, and you created an instance of it and stored it into a variable called myInstance:
- (void)continueSpeaking can be called like so: [myInstance continueSpeaking].
However, the method + (NSArray *)availableVoices can only be called like so: [MyClass availableVoices]
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