Swift: get arbitrary info from UITapGestureRecognizer - ios

Question

I have a list of images within a cell, within a UITableView. For reasons I won't go (too much) into, I can't use didSelectRowAtIndexPath to know which one was selected due to the fact that I am using a third party module that adds its own parent Gestures, and I cannot set cancelsTouchesInView = false (which could technically fix my problem).
In either case, is there a way to add arbitrary info to a view, so that when I receive it in as the sender, I could introspect it.
Eg: if this were HTML & JavaScript, you could do this.
$(myImage).data('foo', 'bar')
$(anotherImage.data('foo', 'thunk')
$('img').on('click', function () {
console.log($(this).data('foo')) // could be "foo" or "thunk"
})
In Swift
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
var cell = MyCustomTableViewCell()
cell.userInteractionEnabled = true
let tapped = UITapGestureRecognizer(target: self, action: Selector("myCallback:"))
cell.addGestureRecognizer(tapped)
// my imaginary world...
cell.foo = self.extraData[indexPath.row]
return cell
}
func myCallback(sender: AnyObject?) {
println(sender.foo)
}
Obviously, the above doesn't work, but is there a way to achieve what I'm trying to do?

Answer 1

Although I personally don't recommend using that much but you can make use of objc_setAssociatedObject if you want to attach extra data to objects at runtime.
Here is one good resource about how to do it in Swift:
http://nshipster.com/swift-objc-runtime/
Alternatively, UIView classes have a property named tag to where you can assign indexPath.row for getting the cell that was tapped on later:
cell.tag = indexPath.row
BTW, you better not be working on cells. Instead, always operate on its contentView property when you want to add gesture or another sub view etc.
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
...
cell.contentView.userInteractionEnabled = true
// Always remove previously added tap gestures because cells are reused
// as you scroll up and down so you'll end up having multiple
// recognizers on the same cell otherwise.
for recognizer in cell.contentView.gestureRecognizers {
cell.contentView.removeGestureRecognizer(recognizer)
}
cell.contentView.addGestureRecognizer(
UITapGestureRecognizer(target: self, action: "myCallback:"))
cell.contentView.tag = indexPath.row
...
return cell
}
It is fairly straightforward to get the cell in call back function:
(Presuming you have only one section so that indexPath.section = 0)
func myCallback(sender: UIGestureRecognizer) {
let indexPath = NSIndexPath(forRow: sender.view.tag , inSection: 0)
if let cell = tableView.cellForRowAtIndexPath(indexPath) {
print("Cell \(cell) has been tapped.")
}
}