How do I read Objective C methods

Question

I think the biggest problem I'm having with understanding programming is understanding what a particular method does. For example

- (BOOL)tableView:(NSTableView *)aTableView shouldEditTableColumn:(NSTableColumn *)aTableColumn row:(NSInteger)rowIndex

When I look at the above method I know that it returns a boolean and that the method receives the following.

1. NSTableView
2. NSTableColumn
3. NSInteger

However, I don't understand what I need to provide to use the method correctly. Do I just return a boolean?

Answer 1

This method will be called by the table (or something) on your delegate (the class you are implementing this method in) when the table needs to know if a certain row and column can be edited. You just need to return YES or NO to indicate if you want to let it be edited.

This is an example implementation:

-(BOOL)tableView:(NSTableView *)aTableView shouldEditTableColumn:(NSTableColumn *)aTableColumn row:(NSInteger)rowIndex {
    return NO;
}

This will mean the table can never be edited.

A more complex implementation like this would let only the first row be editable:

-(BOOL)tableView:(NSTableView *)aTableView shouldEditTableColumn:(NSTableColumn *)aTableColumn row:(NSInteger)rowIndex {
    if (rowIndex == 0)
        return YES;
    else 
        return NO;
    //This can be shortened to:
    //return rowIndex == 0;
}

Answer 2

It comes down to a saying: code tells you how, comments tell you why.

If you are writing a method, you need to know why you want the method and document it accordingly, a.k.a. comments. If you are overriding a method, then you would hope the producer of the method would document about what the method does.

If you're diving into iPhone development without a bit of programming background, you should at least read up the Introduction to The Objective-C Programming Language. If you want to find out what a particular method does in your code, you can always right click the method name and choose "Find Text in Documentation" to read more about it.

Answer 3

The name of the method tableView:shouldEditTableColumn:row: should give you a clue that it is about editing rows and columns in a table view. You could probably guess that, since it is returning a boolean it's called to determine with a table view should edit the supplied row of the supplied column. However, that would just be a guess, so at this point (if I hadn't been using that method only yesterday and thus know exactly what it is for) I would start googling for it (or using Xcode search if I had access to Xcode).

A useful tip for Googling Cocoa documentation is to search only on site:developer.apple.com so we'll try site:developer.apple.com tableView:shouldEditTableColumn:row:. The top hit in this case is NSTableViewDelegate which is the one we want.