如果设置了锚点，如何获取视图的高度

Question

I am currently trying to access the height of a view which I previously set anchors for. So for example, I set the left, right, top, and bottom anchors of searchTable using the following in my ViewController:

searchTable.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
searchTable.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
searchTable.widthAnchor.constraint(equalTo: view.widthAnchor).isActive = true
searchTable.bottomAnchor.constraint(equalTo: menuBar.topAnchor).isActive = true

searchTable is an object of a class that I created that inherits from UIView and has a UIImageView in it. I constrain the UIImageView by using the following in the init function:

imageView.topAnchor.constraint(equalTo: topContainer.topAnchor, constant: 10).isActive = true
imageView.leftAnchor.constraint(equalTo: topContainer.leftAnchor, constant: 10).isActive = true
imageView.heightAnchor.constraint(equalTo: self.heightAnchor, multiplier: topContainerMultiplier * imageProfileMultiplier).isActive = true
imageView.widthAnchor.constraint(equalTo: self.heightAnchor, multiplier: topContainerMultiplier * imageProfileMultiplier).isActive = true

where:

let topContainerMultipler: Double = 1 / 7
let imageProfileMultipler: Double = 1 / 5

Inside the init function of searchTable , I try want to be able to set the corner radius to be half the image size. I tried to use self.frame.height , self.frame.size.height , self.bounds.height and also getting the .constant value of the self.heightAnchor constraint, but all returns 0.

I would think that there is a solution to get around this, but I haven't been able to find it.

Answer 1

You are querying the height of your view's frame after defining your constraints, but before layout has actually resolved those constraints into a frame rectangle. One approach would be to call layoutIfNeeded to force layout to happen immediately, then use view.frame.size.height . The init method is probably not an appropriate place to do this, as opposed to perhaps inside viewDidLoad on the controller. Or you might do this in viewDidLayoutSubviews to recalculate the corner radius every time your view's layout is updated (in which case you won't need layoutIfNeeded ).

Answer 2

Don't use a height constraint if you already use top, bottom, leading, and trailing.

Try to visually debug your view by adding a background color, or using the debug view hierarchy button.

To get the height of a view you should use view.frame.size.height

EDIT (OP question edited)

Your problem is that you try to access the object height when it's just initialized but not displayed yet. You should create a function that update your UI and call it after your view is loaded.