How do I link a UIButton to my data object? (iPhone / Objective C)

Question

I'm new to iPhone dev. My app is dynamically creating buttons, following from my data model. The model isn't just a simple list; it's a tree. I need some way to correlate a created button to that data model, so that when the button is clicked I know what part of the model it corresponds to.

On Windows, most UI controls have a "tag" field where you could put custom data. Using a similar pattern, what I'd like to do on the iPhone is this:

- (void)createMyButton:(MyModel*)foo
{
  UIButton* button = <insert creation code here>
  [button addTarget:self action:@selector(handleCreatedButtonTouch:) ...];
  button.tag = foo;
}

- (void)handleCreatedButtonTouch:(id)sender
{
  UIButton* button = (UIButton*)sender;
  MyModel* foo = (MyModel*)(button.tag);
  [foo userTouchedMyButton];
}

I can't find any mention of such a field in the Apple documentation. How do you iPhone gurus do this? Again, I don't have any simple way of indexing into my data model, and doing an enumeration over the entire data model to find a match seems very wrong.

Answer 1

Andrew,

UI elements in the iPhone SDK have a tag property similar to what you are describing. If you're looking to use button.tag, then you can do so out of the box.

The only change to your pseudo-code would be in your handleCreatedButtonTouch: method. the line:

MyModel* foo = (MyModel *)(button.tag);

would try to cast the tag property to a MyModel object. You would probably want to create an initializer in MyModel to that handles the lookup, such as:

MyModel *foo = [[MyModel alloc] initFromButtonWithTag:[sender tag]];

Hope this helps.