UIView does not have a member named, "inertia" - ios

Question

I am attempting to create a button programmatically that will fade out when tapped, change the text, then fade back in. However, when i try to write the code for the fade animation, I get the error, "'UIView' does not have a member named 'inertia' Inertia is the name of the button, of course.
Here is my code for creating the button, it is within a function that is called within the viewDidLoad() function:
var inertia = UIButton.buttonWithType(UIButtonType.System) as UIButton
inertia.frame = CGRectMake(firstView.frame.width/2-(inertia.frame.width/2), firstView.frame.height/10, firstView.frame.width, firstView.frame.height/10)
inertia.frame = CGRectMake(firstView.frame.width/2-(inertia.frame.width/2), firstView.frame.height/10, firstView.frame.width, firstView.frame.height/10)
inertia.setTitle("Newton's First Law of Motion", forState: UIControlState.Normal)
inertia.addTarget(self, action: "tapped:", forControlEvents: .TouchUpInside)
self.firstView.addSubview(inertia)
This is my line of code for when the button is tapped so far, where the error occurs:
UIView.animateWithDuration(0.4, animations: {self.firstView.inertia.alpha = 0})
I believe I am missing something in the button creation, because when I create an outlet for a button from the storyboard the fade animation will not produce an error.
Please help me fix this issue as I will be using this often. Also if you could find a way for me to create the button's frame properly without having to declare it twice that would be helpful as well.
What I have tried (to no avail):
I have put : UIButton! after var inertia
I have tried `UIView.animateWithduration(0.4, animations: {self.inertia.alpha = 0})

Answer 1

Just to break down the problem line, specifically self.firstView.inertia.alpha. Self is obviously whatever class instance you are in. I assume from the error you are reporting and your code that firstView is a UIView. Now you have added inertia as a subview of firstView, but that does not create a property named inertia on the view. In other words, there is no firstView.inertia. What firstView has is a subviews property which is an array of anyobject.
In other words the button that you created and called inertia is now somewhere in the array firstView.subviews, though it's hard to say where depending on how many other views it has as subviews.
You could iterate through the subviews array to find the button which you'd previously called inertia, but it might be simpler to just keep a reference to inertia. You could make it a property in your class (if there is only one such button) and the call your code with
UIView.animateWithDuration(0.4, animations: {self.inertia.alpha = 0})

Answer 2

As I understand from your description you code looks something like this:
class ViewController:UIViewController {
var firstView:UIView!
func tapped(button: UIButton) {
UIView.animateWithDuration(0.4) { self.firstView.inertia.alpha = 0 }
}
override func viewDidLoad() {
super.viewDidLoad()
var inertia = UIButton.buttonWithType(UIButtonType.System) as UIButton
inertia.frame = CGRectMake(firstView.frame.width/2-(inertia.frame.width/2), firstView.frame.height/10, firstView.frame.width, firstView.frame.height/10)
inertia.frame = CGRectMake(firstView.frame.width/2-(inertia.frame.width/2), firstView.frame.height/10, firstView.frame.width, firstView.frame.height/10)
inertia.setTitle("Newton's First Law of Motion", forState: UIControlState.Normal)
inertia.addTarget(self, action: "tapped:", forControlEvents: .TouchUpInside)
self.firstView.addSubview(inertia)
}
}
Now, you get that error because inerta is not declared as a property in your class, you only create it in a function. If you want to use that button when pressed in tapped() then simply change:
UIView.animateWithDuration(0.4) { self.firstView.inertia.alpha = 0 }
// To
UIView.animateWithDuration(0.4) { button.alpha = 0 } // When TouchUpInside the button will pass itself
Or you can make it a propery by adding:
var inertia:UIButton! // Under class ...
And remove var in viewDidLoad when setting it.