Animate Constraint Multipliers | raywenderlich.com

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This is a companion discussion topic for the original entry at https://www.raywenderlich.com/18411703-uikit-animation/lessons/6
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Jessy, I was curious as to why when looping throw the constraints using the .firstItem and .firstAttribute conditions the value is as an optional before accessing the constant

constraints.first {
$0.firstItem === titleLabel && $0.firstAttribute == .centerX
}?.constant = menuIsOpen ? -100 : 0

But when looping through the constraints using the identifier the value is forced unwrapped to access the isActive property.

constraints.first {
$0.identifier == “Title Center Y”
}!.isActive = false

Wouldn’t both of these options of finding the constraint be an optional instead?

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Hi Kenneth,

Because we know for sure that both of these constraints are going to be found, force-unwrapping is more informative. However, optional chaining also compiles, as you see, so I, as the programmer, wasn’t forced by the compiler to use a “!”. (If a matching constraint wasn’t found for your first example, then nothing would happen.)

I should have used a ! in both cases, for consistency, but you’re free to use whichever option you prefer.

4

Thanks Jessy for the confirmation. However, in this case, although I know for sure the constraints exist, I’m always reluctant to force unwrap anything unless absolutely necessary. But either way it works perfectly and I appreciate the quick response.

And it goes without saying, it’s a great course! It even helped me get a better grasp on using constraints programmatically.

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