What is the Objective-C equivalent for "toString()", for use with NSLog?

Question

Is there a method that I can override in my custom classes so that when

      NSLog(@"%@", myObject) 

is called, it will print the fields (or whatever I deem important) of my object? I guess I'm looking for the Objective-C equivalent of Java's toString().

Answer 1

It is the description instance method, declared as:

- (NSString *)description

Here's an example implementation (thanks to grahamparks):

- (NSString *)description {
   return [NSString stringWithFormat: @"Photo: Name=%@ Author=%@", name, author];
}

Answer 2

Add this to the @implementation of your Photo class:

- (NSString *)description {
   return [NSString stringWithFormat:@"Photo: Name=%@ Author=%@",name,author];
}

Answer 3

You can override the description method of NSObject:

- (NSString *)description

On the subject of logging I recommend this blog post for better logging in Objective-C.

Answer 4

There are two functions that you can use.

- (NSString*)description

This will be displayed when you put your object as, I.E. a parameter for NSLog. The other description function is:

- (NSString*)debugDescription

This will be called when you do po anInstanceOfYourClass in the debug command window. If your class doesn't have a debugDescription function, then just description will be called.

Note that the base class NSObject does have description implemented, but it is fairly bare-bones: it only displays the address of the object. This is why I recommend that you implement description in any class you want to get info out of, especially if you use the description method in your code. If you do use description in your code, I suggest you implement debugDescription as well, also making debugDescription more verbose.

Answer 5

This will output the available voices:

    NSLog((@"speechVoices:%", [[AVSpeechSynthesisVoice speechVoices] description] ));

Answer 6

I think comment from @Nuthatch of overriding "description" with CoreData (i.e classes inheriting NSManagedObject) should be emphasized

https://developer.apple.com/documentation/coredata/nsmanagedobject?language=objc

Avoid overriding description—if this method fires a fault during a debugging operation, the results may be unpredictable.