Can't understand the meaning of this syntax...

Question

I'm about two weeks into writing Cocoa, and about 1/3 of the way through Aaron Hillegass's book, which has been instrumental. I'm really starting to get the hand of things in Object-C, but I can't seem to grasp this syntax concept:
- (id) tableView:(NSTableView *)aTableView
objectValueForTableColumn:(NSTableColumn *)aTableColumn
row:(int)row;
This one is placed in my .h file, but I can't make sense of it. I think it stems from even the basics of something like this:
- (void)clearText:(id)sender
It's the stuff AFTER the semi colon that I don't quite understand. And the first example even takes it further! I just don't feel comfortable going, "Ehh, just type it in like the book says.". Can anyone put this into laymen's terms for me? Thanks for helping out a beginner. ^_^

Answer 1

First of all, the brackets are took off because it's used to create an external link...
However you can use { code } markups (without spaces in it) like that :
{ code }
// your code
{ code }
gives without spaces inside the braces :
// your code
Now let's get back to your code... Everything you said is not really true, so I'm going to correct a few thing, and also correct your code a little...
ejtrowbridge wrote:
Alright, I've done some more brainstorming, and I might have answered my own question. If someone could just verify (or modify!) my reasoning, I'm set!
So here's some example code:
- (void)setPersonName:(NSString *)aName
aName = [aName copy];
[personName release];
personName = aName;
*The Breakdown:*
- The method name is "setPersonName".
- setPersonName is not returning anything.
- setPersonName is allowing the variable "aName" to be modified which is strict typed to a NSString.
- The instance variable personName is cleared of any previous value.
- The instance variable personName is given the same value of "aName" that was passed into the method.
Is that right? Let me try one more to see if I got it:
Okay so your breakdown has some errors :
- the name of the method is not "setPersonName" but really "setPersonName:" the colons are part of the name, and it's better to remember it.
- setPersonName: takes one argument of type "NSString *" (which is indeed strictly typed) and named "aName".
The correct code for that function is :
- (void)setPersonName:(NSString *)aName
[personName release];
personName = [aName copy];
Okay some precisions, we call that method a setter, it's a specific kind of method, the name generally starts with the word "set" followed by the instance variable name that it modify with its start letter in capital, it returns "void" and takes one argument which is the new value of the instance variable and so it's the same type.
ejtrowbridge wrote:
*Example code:*
- (float)expectedRaise
return expectedRaise;
- (void)setExpectedRaise:(float)x
expectedRaise = x;
*The Breakdown:*
- The method expectedRaise will be returning a float value.
- Then it returns whatever expectedRaise's float value is.
- The method setExpectedRaise will not be returning anything.
- Will accept outside changes to the variable "x" which is strict typed to a float value.
- Then the method sets the instance variable expectedRaise to the value of "x" which was passed in from outside.
Here everything is good, accessor methods for non-object instance variable are pretty simple.
ejtrowbridge wrote:
Is this how I should be interpreting accessor methods? If this is right, then I will feel more comfortable moving forward in the book. This seems like it is used ALOT, so I wanted to make sure I was headed in the right direction. If it is, the only questions is where the "aName" and "x" values come into play... but maybe I'm getting ahead of myself.
So yes, it's how you should. And yes it's used a lot, that's a basis of Object-Oriented Programming. We encapsulate the values of our classes, they're not accessible from the outside, so we use accessor methods to allow the users to touch it BUT under our control, if you want to modify the accessor methods to make a specific behavior you can, for example, let say you a percentage in a class and you don't want it to be superior to 100, you can write that :
- (void)setPercent:(int)aValue
if(aValue > 100)
aValue = 100;
percent = aValue;
With that code you're sure that percent will never be over 100. So with the accessor methods you keep the control of your instance variable and avoid the user to corrupt the object datas.