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I’m trying to understand an error message I get after many NSLog and breakpoints… I get this as output :

*** +[NSMutableArray count]: selector not recognized

How can’t NSMutableArray understand the method “count” ? It’s a rather basic method…

Another strange thing arrises when I check my multiple logs. I try to get a description of a NSMutableArray and the output is :


I thought that I would get something like (object1,object2,…). Can anyone explain why all of this happens ?

– Trax

Look carefully at the output you just copied.

The runtime spat out a +[NSMutableArray count]: selector not recognized, not a -[NSMutableArray count]: selector not recognized message. That means you’re trying to send +count to a Class, but there is no class method +count in NSMutableArray. It’s an instance method, so instead of typing [NSMutableArray count]; you should use [myMutableArray count];. –KevinPerry

Do it like this to see what he means. Create a foundation tool, and add this inside the int main() brackets.

NSMutableArray * myMutableArray; //declares a pointer to NSMutableArray int count; //declares in integer called count int i; //declares an integer called i myMutableArray = [[NSMutableArray alloc]init]; //allocates and inits myMutableArray [myMutableArray addObject:@”This is the first object to count”]; [myMutableArray addObject:@”This is the second object to count”]; count = [myMutableArray count]; //Uses an INSTANCE method, count. for (i = 0; i < (count - 1); i++) //Starts a for loop. { NSLog(@”At index %i, the object is %@”, i, [myMutableArray objectAtIndex:i]); /* What this does is it NSLogs (A function similar to printf, with object compatability, see NSLog) i (which is incremented each time by the for loop) and the object at the index i. The for loop increments i until it is at the index of the last object, by saying it is less than count - 1. */ }

That is a small project to show how to use the count method, and the usefulness of it. You could do it with an enumerator too (see NSEnumerator), but for this example, you can see how count works. Basically, the difference with a class method (like alloc) and an instance method (like count) is what you want to send it to. You’ll need to create an instance of the class NSMutableArray (see the first line), in order to have something to properly send the message to.


Okay, here’s what I do EXACTLY… I have two custom classes of NSView… Say view1 and view2…

view1 has a NSMutableArray instance variable. In that array, there are NSNumber objects, NSString objects and NSMutableArray objects… view2 has also a MSMutableArray instance variable. I want the view2’s NSMutableArray to become exactly like an array contained in view1… I tried to do this with an accessor method, something common :

[toView2 chListe:[lisPrin objectAtIndex:pos+2]];

In the example above, which is a line of code taken from the implementation of view1, toView2 is an outlet connected to view2. chListe is the function I want view1 to execute. And the objectAtIndex points to a NSMutableArray.

I hope you won’t be confused… To make it simple, I want view1 to tell view2 to change its array so it’s the same as the array designed by objectAtIndex…

I do a similar thing except with NSTableView. Whenever you change selections in on table view, it triggers the other’s datasource to point to a different array and reload data. Assuming lisPrin is an NSMutableArray within view1 and “pos+2” truly does point to an NSMutableArray, the code at this level appears fine. I would say that your troubles aren’t here but within the chListe method within view2. What does that code look like?