Question

I’m starting to learn how to read message syntax in Objective-C and want to reinforce good understanding of message syntax (I come from a Java/C#/Ruby background).

I’m currently looking at the statement:

[self.view addSubview:label];

“Send this message to the addSubView method, with label as the argument, the mthod is on the view object on self. “

(“on” isn’t really a great way to describe the “dot notation” for the objects. I’m open to a better way to transcribe it!)

How do you read and interpret the above statement?

Answer 1

This is actually a nested message send, althogh the dot syntax makes that confusing.* The distinction between messages and methods in ObjC can also be a bit confusing at first. Generally, one can talk about them as equivalent, but strictly, a message is sent to an object; the message is looked up in the object’s method list, and then the associated method is called.**

It can be rewritten:

[[self view] addSubview:label];

So the message view is being sent to self, the reciever. The result of that is then in the receiver position for the other message, which is addSubview:. You’re right about label being the argument to addSubview:.

In English, then, this is: “Add label as a subview of self‘s view” or “send addSubview:, passing label, to the result of sending view to self“.

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*The dot syntax is intended as sugar for property access, that is, for using the property’s setter and getter methods; by default, the name of the getter is the same as the name of the property itself.

**Should the method not be found, the object can do other things with the message. The only real difference that this method/message distinction makes is that the method associated with a message can be changed at runtime — dynamic binding.