Messages not understood

Debugger messages stating <class or object> does not understand <message> are probably the most common errors. The causes include:

•	Misspelling the message selector

•	Sending the message to a class that does not support it

•	Sending the message to the wrong object

•	Passing the wrong number of arguments

•	Omitting a period or semicolon on the previous statement

•	Omitting or mismatching parentheses

•	Sending the message to an object that is nil

•	Implementing a class method as an instance method, or vice versa