On 2010-05-25 15.38, Steven Schveighoffer wrote:
On Tue, 25 May 2010 09:26:20 -0400, Jacob Carlborg <d...@me.com> wrote:
On 2010-05-24 21.08, Steven Schveighoffer wrote:
Don't user interface objects have data? If a UI component is an
interface, how does it expose access to its data? For example, a .NET
ListView control contains an Items property which you can use to access
the elements in the list view. The Items property returns a
ListViewItemCollection which implements IList, IContainer, and
IEnumerable. I've found these types of abstractions useful when
adding/iterating, etc.
-Steve
I would say that is a bad design, I would go with the MVC pattern. For
example, you have a ListView and when it's ready to display, say row
3, it calls your delegate and request you to return the item that
should be visible on row 3. Then it's up to you to store the items in
some appropriate data structure, like a list or array.
I don't know if a delegate is enough to implement the pattern. What you
need is a set of delegates that perform operations on the container. Oh
wait, that's an interface!
What I was trying to say is that a ListView should not contain a data
structure. I try to explain that I want to say in code instead:
auto data = new Item[10];
auto listView = new ListView;
listView.numberOfRows = size_t delegate (ListView lv) {
return data.length;
}
listView.itemAtRow = Item delegate (ListView lv, size_t row) {
return data[row];
}
Now Item could be an interface but it don't have to be. I suggest you
have a look at Apple's documentation of NSTableView:
*
http://developer.apple.com/mac/library/documentation/Cocoa/Reference/ApplicationKit/Classes/NSTableView_Class/Reference/Reference.html
*
http://developer.apple.com/mac/library/documentation/cocoa/Conceptual/TableView/Tasks/UsingTableDataSource.html#//apple_ref/doc/uid/20000117
One interesting difference between an interface and a delegate is that
an interface is a single pointer, whereas a delegate is two. With the
context-pointer design, many more features are possible. For instance,
struct interfaces would be easy, as well as easily tacking on an
interface to a class.
In any case, Windows Forms is probably the easiest UI toolkit I've
worked with (which isn't saying much), I don't think it's a bad design.
That could be the Visual Studio talking though :)
I suggest you have a look at Cocoa, it uses the MVC pattern.
-Steve
--
/Jacob Carlborg
