Could not cast value of type - ios

Question

I am creating a Tic Tac Toe app. When the game resets, all the Xs and Os UIButton images should return to nil. Each space in the board is tagged from 0 to 8.
var buttonsToClear : UIButton
for var i = 0; i < 9; i++ {
buttonsToClear = view.viewWithTag(i) as! UIButton
buttonsToClear.setImage(nil, forState: .Normal)
}
Everything worked fine until I added a Navigation Bar. Now I get the error message
"Could not cast value of type '_UINavigationBarBackground' (0x107e2f2a0) >to 'UIButton' (0x107e357e0).
(lldb)
I am absolutely certain that my new Navigation Bar has a tag of "10".
What else could be triggering this message?

Answer 1

You should not use 0 tag, due to 0 is default and you can get any view (in this case the background of the navigation).
Tag the views starting by 1.

Answer 2

You are logically right and your code will work perfectly.
You are getting the error
"Could not cast value of type '_UINavigationBarBackground'
(0x107e2f2a0) >to 'UIButton' (0x107e357e0). (lldb)
Because, when your for loop runs, the first index will be zero i.e. i = 0,
buttonsToClear = view.viewWithTag(i) as! UIButton
will become
buttonsToClear = view.viewWithTag(0) as! UIButton
So in this case you are trying to get the view with tag value 0.
UINavigationBarBackground also has tag value 0.
Note:
1. when system finds two view with same tag value, and you are trying to get view using viewWithTag: it will return first view.
2. Every View Has default tag value 0.
3. Just drag UILabel or UIView in storyboard or XIB and check its tag value.
So in your case it will return UINavigationBarBackground instead of UIButton. So you can't type-cast UINavigationBarBackground into UIButton.
Solution of your Error :
Never give tags starting from 0.
Try to give tags starting for some value like 1000.
so your first button will have tag 1000, next will have 1001, then 1002 and so-on.
write your for loop as below.
var buttonsToClear : UIButton
for var i = 1000; i < 1009; i++ {
buttonsToClear = view.viewWithTag(i) as! UIButton
buttonsToClear.setImage(nil, forState: .Normal)
}

Answer 3

You must be able to see the stack trace to see where this is being triggered? In any case, the obvious solution is to run this in the debugger, turn on exception breakpoints and see what's going on.
And as Jose says, don't use Tag 0.

Answer 4

You need a new approach that doesn't rely on only using tags to identify your subviews
The problem is, your loop is coming across a private property on UINavigationBar, _UINavigationBarBackground. Because you can't set the tag on this, it will have the default tag of 0. Therefore you will attempt to send a UIButton function to it.
I would simply loop through your subviews and check if a view is of type UIButton, and then check it's tags (be sure still not to use tag 0, as that is the default tag) before removing it. That way you are 100% sure that you've gotten the right subview.
var buttonsToClear : UIButton
for view in view.subviews { // Loop through subviews
if let button = view as? UIButton { // Check if UIButton
if button.tag > 0 || button.tag < 10 { // Check tags
buttonsToClear = button
buttonsToClear.setImage(nil, forState: .Normal)
}
}
}