Handling UIView/UIScrollView With Unknown Size (AutoLayout/Swift) [closed]

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I have a view in my app that is structured like so;

UIViewController (self)
- UIView (self.view)
  - UIScrollView (scrollView)
    - UIView (contentView)
      - UIView (subviewA)
      - UIView (subviewB)
      - UIView (subviewC)

After reading a variety of posts on UIScrollView (see here and here), I now have a UIScrollView that looks properly, but doesn't actually scroll. I believe this is because my three subviews (subviewA, subviewB, and subviewC) are all built with AutoLayout.

My contentView has a bottom constraint of contentView.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor).isActive = true

Ideally, I'd like my contentView's bottom anchor to actually be at the bottom of subviewC, but since subviewC is built with AutoLayout, it doesn't have a defined size when it is added to to contentView, and thus, the scrollView doesn't actually scroll.

Can anyone advise why my scroll does does not scroll vertically? It does appear that the subviews are all being added, but the lowest subview is well off-screen and doesn't actually allow me to scroll.

(There's a little bit more to this, such as how I'd like contentView to have a border that surrounds subviewA, subviewB, and subviewC, but I feel resolving the scroll issue will probably lead me down the right path on that).

@mag_zbc Updated for clarity. Specifically, my UIScrollView does not scroll vertically, even though all of my subviews are being added. I suspect this is due to the subviews not having a physical size as they are all built with autolayout. — ZbadhabitZ
– ZbadhabitZ, Commented May 20, 2019 at 15:16
Autolayout is perfectly fine to use in scroll view contents, as long as its done in such a way that the scroll view can calculate its content's height precisely. See my answer below. — NRitH
– NRitH, Commented May 20, 2019 at 15:25
@RajeshKumarR - They are all a variety of components; UILabels, UIViews, UITextField, etc. They do have defined constants in terms of their placement and size, but the views themselves (subviewA, subviewB, subviewC) do not have defined sizes. — ZbadhabitZ
– ZbadhabitZ, Commented May 20, 2019 at 15:48

NRitH · Accepted Answer · 2019-05-20 15:35:08Z

1

A scroll view has to be able to calculate the size of its contents, so yes, your contentView's top constraint should match subviewA's top, and contentView's bottom should match subviewC's bottom. It's perfectly fine that all the subviews use constraints, as long as the subviews' tops and bottoms are constrained.

Once your contentView is constrained to its subviews, constrain all 4 of its edges to the scrollView's edges. (If you don't want it to scroll horizontally, then also constrain the contentView's width to be equal to the scrollView's.)

edited May 20, 2019 at 15:35

answered May 20, 2019 at 15:24

NRitH

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8 Comments

ZbadhabitZ Over a year ago

I'm struggling to understand how I can add subviewC to contentView and have it pinned to the bottom of contentView when I actually want the bottom of contentView pinned to the bottom of subviewC. How do I force contentView's bottom anchor to be the bottom of subviewC when subviewC is its child? PS Thank you for the screenshot!

NRitH Over a year ago

subviewC does not have to have an explicit height constraint; it can be a UILabel with 0 lines (meaning it can have any number of lines, which is what I have in my example screenshot). Of course, it can have an explicit height if it's a UIView or other kind of view that doesn't have a "natural" height.

NRitH Over a year ago

"How do I force contentView's bottom anchor to be the bottom of subviewC when subviewC is its child?" I don't understand why this is a problem--just control-drag from subviewC to contentView, and select the bottom constraint.

ZbadhabitZ Over a year ago

Wouldn't this make the bottom constraint of subviewC equal to that of contentView's bottom constraint? Since contentView was added first, and its bottom constraint is equal that of scrollView, I guess I'm confused how pinning the bottom of subviewC will somehow make contentView taller (which seems to be why the scroll view isn't scrolling).

ZbadhabitZ Over a year ago

I think my confusion is coming from; if I add subviews to contentView, doesn't contentView already have to have its constraints set? How can I add subviewA to contentView without defining the constraints of contentView already?

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RajeshKumar R · Accepted Answer · 2019-05-20 16:30:46Z

0

For scrollview add Top, Leading, Trailing, Bottom constraints to its superview with 0 constant.

For ContentView add Top, Leading, Trailing, Bottom constraints to its superview scrollview with 0 constant. And add equal width to the scrollview, then add equal height to the scrollview with priority 999.

Now add Top, Leading, Trailing, Bottom constraints for the subviewA, subviewB, subviewC views.

Then add Top, Leading, Trailing, Bottom, height constraints to the subviews of subviewA, subviewB, subviewC views.

answered May 20, 2019 at 16:30

RajeshKumar R

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