I managed to workaround this issue by create the UIStackView in Objective-C code and get it in swift code as function return value.

@MichaelPei I try this，But always return nil by create the UIStackView in Objective-C code

@mokai Following code works for me

+ (UIStackView *)stackView {
    return [[UIStackView alloc] init];
}

You may have a try. It seems that UIStack implementation is replaced by FDStackView using assembly code, which should works fine in Objective-C runtime.

@mokai if use it as pod, make sure to use it as static library otherwise you could get nil.
I just updated pod to dynamic library and found nil will returned in old method. I have to copy FDStackView files to project to make it work. Ugly, but works.

@MichaelPei Yea，I use it as pod。。。。

At first we disabled availability checks to reference UIStackView in swift code, but it crashes all if #available(iOS 9.0, *) blocks
Then we took this approach when referencing stack view from IB in swift code (extend the protocol as needed to interact with the Stack View). I believe this could be built in the library with the full supported API.

@objc protocol StackableView {
    var arrangedSubviews:[UIView] { get }
    func removeArrangedSubview(view:UIView)
    func layoutIfNeeded()
}
​
@available(iOS 9.0, *)
extension UIStackView: StackableView {

}
​
extension FDStackView: StackableView {

}
​
@IBOutlet var stackViewAnswers: StackableView!