SwiftUI: Center Content in ScrollView - swiftui

Question

I'm trying to center a bunch of views in a VStack within a ScrollView in SwiftUI. To simplify things, I'm just trying to get it to work with a single Text view. Here's what I've come up with so far:
var body: some View {
ScrollView(alwaysBounceVertical: true){
HStack(alignment: .center) {
Spacer()
Text("This Is a Test")
Spacer()
} //HStack
.background(Color.green)
} //ScrollView
.background(Color.gray)
}
This results in this:
I want the text to be in the middle like this:
So the HStack should be full-width and the Text should be centered within it. It seems like this should be easy, but I don't get what I'm doing wrong. :)

Answer 1

Using GeometryReader, you can get information about the size of the containing view and use that to size your view.
var body: some View {
GeometryReader { geometry in <--- Added
ScrollView(alwaysBounceVertical: true){
HStack(alignment: .center) {
Spacer()
Text("This Is a Test")
Spacer()
} //HStack
.frame(width: geometry.size.width) <--- Added
.background(Color.green)
} //ScrollView
.background(Color.gray)
}
}
edit: after looking into this more, it seems that part of the problem is that you are using a ScrollView. If you remove that parent, the spacers in the HStack will automatically cause stretching to fill the view. I'm guessing the automatic stretching doesn't happen in ScrollViews because there's no finite limit to how big it can be, how much would it stretch? (because a ScrollView can scroll in any direction)

Answer 2

This seems to be a bug in Xcode 11.0 beta, ScrollView content wouldn't fill the scroll view. If you replace the ScrollView with a List it will work as expected. But if you have to use a scroll view, one workaround is to fix the scroll view's content width.
So your code will look something like this:
ScrollView(alwaysBounceVertical: true) {
HStack(alignment: .center) {
Spacer()
Text("This Is a Test")
Spacer()
} // HStack
.frame(width: UIScreen.main.bounds.width) // set a fixed width
.background(Color.green)
} // ScrollView
.background(Color.gray)
Result:

Answer 3

You should use the modifier frame and set its maxWidth: .infinity.
So it tells its parent: "the wider, the better" :)
var body: some View {
ScrollView(.vertical, showsIndicators: true){
HStack(alignment: .center) {
Spacer()
Text("This Is a Test")
.frame(maxWidth: .infinity) // <- this
Spacer()
} //HStack
.background(Color.green)
} //ScrollView
.background(Color.gray)
}
And this works regardless its parent.
Scrollview or whatever View it's set in.
Paul is doing a great job clarifying it to all of us here:
https://www.hackingwithswift.com/quick-start/swiftui/how-to-give-a-view-a-custom-frame
Answer compatible with Xcode 12.1 (12A7403)
I hope this helps 👍
dsa