Question

Can anyone enlighten me as to the differences between the two statements below.

[self playButtonSound];

AND:

[self performSelector:@selector(playButtonSound)];

I am just asking as I had some old code that used @selector, now with a little more knowledge I can’t think why I did not use [self playButtonSound] instead, they both seem to do the same as written here.

gary

Answer 1

Both to the same thing, but [self playButtonSound]; is definitely the normal way to invoke a method in Objective-C. However, using performSelector: allows you to call a method that is only determined at runtime.

From the NSObject Protocol Reference:

The performSelector: method is
equivalent to sending an aSelector
message directly to the receiver. For
example, all three of the following
messages do the same thing:

id myClone = [anObject copy];
id myClone = [anObject performSelector:@selector(copy)];
id myClone = [anObject performSelector:sel_getUid("copy")];

However, the performSelector: method
allows you to send messages that
aren’t determined until runtime. A
variable selector can be passed as the
argument:

SEL myMethod = findTheAppropriateSelectorForTheCurrentSituation();
[anObject performSelector:myMethod];