Autolayouts : How to create collapse/Expand dynamic view swift 3/4

问题

I have a problem that I can't create a view that can collapse it's contents that may be dynamic height , i know it's easy to collapse it with height constant = 0 , but i can't figure out how to make it expand again as the content of that view is dynamic and sub-itmes may be added later

I want that behavior

回答1:

Your answer has massively overcomplicated a very simple solution.

You should first create your zeroHeightConstraint as a property.

let zeroHeightConstraint: NSLayoutConstraint = dynamicView.heightAnchor.constraint(equalToConstant: 0)

You could do this as an outlet from the storyboard too if you wanted.

Now add your button action...

@IBAction func toggleCollapisbleView() {
    if animationRunning { return }

    let shouldCollapse = dynamicView.frame.height != 0

    animateView(isCollapse: shouldCollapse,
                buttonText: shouldCollapse ? "Expand" : "Collapse")
}

private func animateView(isCollapse: Bool, buttonText: String) {
    zeroHeightConstraint.isActive = isCollapse

    animationRunning = true

    UIView.animate(withDuration duration: 1, animations: {
        self.view.layoutIfNeeded()
    }, completion: { _ in
        self.animationRunning = false
        self.button.setTitle(buttonText, for: .normal)
    })
}

Always avoid using view.tag in your code. It should always be seen as "code smell". There is almost always a much more elegant way of doing what you are trying to do.

Regarding the bottom constraint. You should really be using a UIStackView to layout the contents of the inside of the view here. By doing that you no longer need to iterate the subviews of your contentView you can access the UIStackView directly. And do the same thing there. In fact... a much better way would be to create the bottomConstraint against the view using a priority less than 1000. e.g. 999.

By doing that you don't have to remove or add that constraint at all. When the zeroHeightConstraint is not active it will be there and work. When the zeroHeightConstraint is active it will override the bottom constraint automatically.

来源：https://stackoverflow.com/questions/48150004/autolayouts-how-to-create-collapse-expand-dynamic-view-swift-3-4

标签

ios

swift

swift3

autolayout