objective-c - Objective C, how to query if an object is of a certain class

Question

I am deriving from TableViewCell. When i query the table view about an index path it returns a UITableViewCell. How do i find if this object is one of my custom type "CustomCell"?

Answer 1

if ([cell isKindOfClass:[CustomCell class]]) {
    [(CustomCell*)cell customCellMethod];
}

Answer 2

if ([cell isKindOfClass:[CustomCell class]]) {
   // ...
}

Answer 3

As always in object-oriented design, trying to use an instance's class identity is a code smell and should raise a flag. What exactly are you trying to do with your custom cell? Perhaps someone can suggest a better approach.

No mater what, it's much better design to depend on an interface (a @protocol in Objective-C speak) than a class as it helps to decouple your design. Define a @protocol with the relevant API you need and have your CustomCell implement that protocol. In your code you can then test:

if([cell conformsToProtocol:@protocol(MyCellProtocol)]) {
  //...
}

rather than testing for class identity.

If you only need a single method, you can use [cell respondsToSelector:@selector(myMethod)].

Answer 4

There are actually two methods you could use here. The one you probably want is isKindOfClass:, but there is another method called isMemberOfClass: and this will only return YES if the receiver is an instance of the provided class, not an instance of a subclass.

For example, if DerivedClass is a subclass of BaseClass, then here are the outcomes of each method:

BOOL isKind = [aDerivedInstance isKindOfClass:[BaseClass class]]; // YES
BOOL isMember = [aDerivedInstance isMemberOfClass:[BaseClass class]]; // NO