How to make a SwiftUI List scroll automatically?
Update: In iOS 14 there is now a native way to do this. I am doing it as such
ScrollViewReader { scrollView in
ScrollView(.vertical) {
LazyVStack {
ForEach(notes, id: \.self) { note in
MessageView(note: note)
}
}
.onAppear {
scrollView.scrollTo(notes[notes.endIndex - 1])
}
}
}
For iOS 13 and below you can try:
I found that flipping the views seemed to work quite nicely for me. This starts the ScrollView at the bottom and when adding new data to it automatically scrolls the view down.
- Rotate the outermost view 180
.rotationEffect(.radians(.pi)) - Flip it across the vertical plane
.scaleEffect(x: -1, y: 1, anchor: .center)
You will have to do this to your inner views as well, as now they will all be rotated and flipped. To flip them back do the same thing above.
If you need this many places it might be worth having a custom view for this.
You can try something like the following:
List(chatController.messages, id: \.self) { message in
MessageView(message.text, message.isMe)
.rotationEffect(.radians(.pi))
.scaleEffect(x: -1, y: 1, anchor: .center)
}
.rotationEffect(.radians(.pi))
.scaleEffect(x: -1, y: 1, anchor: .center)
Here's a View extension to flip it
extension View {
public func flip() -> some View {
return self
.rotationEffect(.radians(.pi))
.scaleEffect(x: -1, y: 1, anchor: .center)
}
}
As there is no built-in such feature for now (neither for List nor for ScrollView), Xcode 11.2, so I needed to code custom ScrollView with ScrollToEnd behaviour
!!! Inspired by this article.
Here is a result of my experiments, hope one finds it helpful as well. Of course there are more parameters, which might be configurable, like colors, etc., but it appears trivial and out of scope.
import SwiftUI
struct ContentView: View {
@State private var objects = ["0", "1"]
var body: some View {
NavigationView {
VStack {
CustomScrollView(scrollToEnd: true) {
ForEach(self.objects, id: \.self) { object in
VStack {
Text("Row \(object)").padding().background(Color.yellow)
NavigationLink(destination: Text("Details for \(object)")) {
Text("Link")
}
Divider()
}.overlay(RoundedRectangle(cornerRadius: 8).stroke())
}
}
.navigationBarTitle("ScrollToEnd", displayMode: .inline)
// CustomScrollView(reversed: true) {
// ForEach(self.objects, id: \.self) { object in
// VStack {
// Text("Row \(object)").padding().background(Color.yellow)
// NavigationLink(destination: Text("Details for \(object)")) {
// Image(systemName: "chevron.right.circle")
// }
// Divider()
// }.overlay(RoundedRectangle(cornerRadius: 8).stroke())
// }
// }
// .navigationBarTitle("Reverse", displayMode: .inline)
HStack {
Button(action: {
self.objects.append("\(self.objects.count)")
}) {
Text("Add")
}
Button(action: {
if !self.objects.isEmpty {
self.objects.removeLast()
}
}) {
Text("Remove")
}
}
}
}
}
}
struct CustomScrollView<Content>: View where Content: View {
var axes: Axis.Set = .vertical
var reversed: Bool = false
var scrollToEnd: Bool = false
var content: () -> Content
@State private var contentHeight: CGFloat = .zero
@State private var contentOffset: CGFloat = .zero
@State private var scrollOffset: CGFloat = .zero
var body: some View {
GeometryReader { geometry in
if self.axes == .vertical {
self.vertical(geometry: geometry)
} else {
// implement same for horizontal orientation
}
}
.clipped()
}
private func vertical(geometry: GeometryProxy) -> some View {
VStack {
content()
}
.modifier(ViewHeightKey())
.onPreferenceChange(ViewHeightKey.self) {
self.updateHeight(with: $0, outerHeight: geometry.size.height)
}
.frame(height: geometry.size.height, alignment: (reversed ? .bottom : .top))
.offset(y: contentOffset + scrollOffset)
.animation(.easeInOut)
.background(Color.white)
.gesture(DragGesture()
.onChanged { self.onDragChanged($0) }
.onEnded { self.onDragEnded($0, outerHeight: geometry.size.height) }
)
}
private func onDragChanged(_ value: DragGesture.Value) {
self.scrollOffset = value.location.y - value.startLocation.y
}
private func onDragEnded(_ value: DragGesture.Value, outerHeight: CGFloat) {
let scrollOffset = value.predictedEndLocation.y - value.startLocation.y
self.updateOffset(with: scrollOffset, outerHeight: outerHeight)
self.scrollOffset = 0
}
private func updateHeight(with height: CGFloat, outerHeight: CGFloat) {
let delta = self.contentHeight - height
self.contentHeight = height
if scrollToEnd {
self.contentOffset = self.reversed ? height - outerHeight - delta : outerHeight - height
}
if abs(self.contentOffset) > .zero {
self.updateOffset(with: delta, outerHeight: outerHeight)
}
}
private func updateOffset(with delta: CGFloat, outerHeight: CGFloat) {
let topLimit = self.contentHeight - outerHeight
if topLimit < .zero {
self.contentOffset = .zero
} else {
var proposedOffset = self.contentOffset + delta
if (self.reversed ? proposedOffset : -proposedOffset) < .zero {
proposedOffset = 0
} else if (self.reversed ? proposedOffset : -proposedOffset) > topLimit {
proposedOffset = (self.reversed ? topLimit : -topLimit)
}
self.contentOffset = proposedOffset
}
}
}
struct ViewHeightKey: PreferenceKey {
static var defaultValue: CGFloat { 0 }
static func reduce(value: inout Value, nextValue: () -> Value) {
value = value + nextValue()
}
}
extension ViewHeightKey: ViewModifier {
func body(content: Content) -> some View {
return content.background(GeometryReader { proxy in
Color.clear.preference(key: Self.self, value: proxy.size.height)
})
}
}
#if DEBUG
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
#endif
You can do this now, since Xcode 12, with the all new ScrollViewProxy, here's example code:
You can update the code below with your chatController.messages and the call scrollViewProxy.scrollTo(chatController.messages.count-1).
When to do it? Maybe on the SwiftUI's new onChange!
struct ContentView: View {
let itemCount: Int = 100
var body: some View {
ScrollViewReader { scrollViewProxy in
VStack {
Button("Scroll to top") {
scrollViewProxy.scrollTo(0)
}
Button("Scroll to buttom") {
scrollViewProxy.scrollTo(itemCount-1)
}
ScrollView {
LazyVStack {
ForEach(0 ..< itemCount) { i in
Text("Item \(i)")
.frame(height: 50)
.id(i)
}
}
}
}
}
}
}
SwiftUI 2.0 - iOS 14
this is the one: (wrapping it in a ScrollViewReader)
scrollView.scrollTo(rowID)
With the release of SwiftUI 2.0, you can embed any scrollable in the ScrollViewReader and then you can access to the exact element location you need to scroll.
Here is a full demo app:
// A simple list of messages
struct MessageListView: View {
var messages = (1...100).map { "Message number: \($0)" }
var body: some View {
ScrollView {
LazyVStack {
ForEach(messages, id:\.self) { message in
Text(message)
Divider()
}
}
}
}
}
struct ContentView: View {
@State var search: String = ""
var body: some View {
ScrollViewReader { scrollView in
VStack {
MessageListView()
Divider()
HStack {
TextField("Number to search", text: $search)
Button("Go") {
withAnimation {
scrollView.scrollTo("Message number: \(search)")
}
}
}.padding(.horizontal, 16)
}
}
}
}
Preview
This can be accomplished on macOS by wrapping an NSScrollView inside an NSViewControllerRepresentable object (and I assume the same thing work on iOS using UIScrollView and UIViewControllerRepresentable.) I am thinking this may be a little more reliable than the other answer here since the OS would still be managing much of the control's function.
I just now got this working, and I plan on trying to get some more things to work, such as getting the position of certain lines within my content, but here is my code so far:
import SwiftUI
struct ScrollableView<Content:View>: NSViewControllerRepresentable {
typealias NSViewControllerType = NSScrollViewController<Content>
var scrollPosition : Binding<CGPoint?>
var hasScrollbars : Bool
var content: () -> Content
init(hasScrollbars: Bool = true, scrollTo: Binding<CGPoint?>, @ViewBuilder content: @escaping () -> Content) {
self.scrollPosition = scrollTo
self.hasScrollbars = hasScrollbars
self.content = content
}
func makeNSViewController(context: NSViewControllerRepresentableContext<Self>) -> NSViewControllerType {
let scrollViewController = NSScrollViewController(rootView: self.content())
scrollViewController.scrollView.hasVerticalScroller = hasScrollbars
scrollViewController.scrollView.hasHorizontalScroller = hasScrollbars
return scrollViewController
}
func updateNSViewController(_ viewController: NSViewControllerType, context: NSViewControllerRepresentableContext<Self>) {
viewController.hostingController.rootView = self.content()
if let scrollPosition = self.scrollPosition.wrappedValue {
viewController.scrollView.contentView.scroll(scrollPosition)
DispatchQueue.main.async(execute: {self.scrollPosition.wrappedValue = nil})
}
viewController.hostingController.view.frame.size = viewController.hostingController.view.intrinsicContentSize
}
}
class NSScrollViewController<Content: View> : NSViewController, ObservableObject {
var scrollView = NSScrollView()
var scrollPosition : Binding<CGPoint>? = nil
var hostingController : NSHostingController<Content>! = nil
@Published var scrollTo : CGFloat? = nil
override func loadView() {
scrollView.documentView = hostingController.view
view = scrollView
}
init(rootView: Content) {
self.hostingController = NSHostingController<Content>(rootView: rootView)
super.init(nibName: nil, bundle: nil)
}
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
override func viewDidLoad() {
super.viewDidLoad()
}
}
struct ScrollableViewTest: View {
@State var scrollTo : CGPoint? = nil
var body: some View {
ScrollableView(scrollTo: $scrollTo)
{
Text("Scroll to bottom").onTapGesture {
self.$scrollTo.wrappedValue = CGPoint(x: 0,y: 1000)
}
ForEach(1...50, id: \.self) { (i : Int) in
Text("Test \(i)")
}
Text("Scroll to top").onTapGesture {
self.$scrollTo.wrappedValue = CGPoint(x: 0,y: 0)
}
}
}
}