SwiftUI 2.0 增加了滚动定位功能，已经可以较轻松的适应大多数场景的应用。实现手段完全不同于之前民间的各种解决方案，并不是通过设置具体的 offset 来进行定位，而是使用 id 来进行位置标记。
基本用法——实现从右向左滚动
Swift
struct ScrollReaderTest: View {
var body: some View {
ScrollView(.horizontal) {
//类似 GeometryReader 的使用方式，设定滚动定位区域
ScrollViewReader{ proxy in
Rectangle()
.fill(LinearGradient(
gradient: Gradient(colors: [.blue,.red]),
startPoint: .leading,
endPoint: .trailing))
.frame(width: 1000, height: 300, alignment: .center)
.id("rec") //为 ScrollView 中需要定位的 View 设置 id
.onAppear {
//滚动到指定 id 的位置，按照 anchor 的设置来对齐
proxy.scrollTo("rec",anchor:.trailing)
}
}
}
}
}通过按钮来滚动到指定位置
Swift
import SwiftUI
struct ScrollReadeTest: View {
private var list = ScrollItem.items(300)
@State private var position:Int = 0
var body: some View {
NavigationView{
ScrollView{
ScrollViewReader{ proxy in
LazyVStack{
ForEach(list,id:\.id){ item in
Text(item.title).id(item.id)
}
}
.onChange(of: position) { positon in
switch position{
case 1:
let id = list.first!.id
withAnimation(Animation.easeInOut){
proxy.scrollTo(id,anchor:.top)
}
case 2:
let id = list[Int(list.count / 2)].id
withAnimation(Animation.easeInOut){
proxy.scrollTo(id,anchor:.center)
}
case 3:
let id = list.last!.id
withAnimation(Animation.easeInOut){
proxy.scrollTo(id,anchor:.bottom)
}
default:
break
}
}
}
}
.navigationTitle("滚动定位")
.toolbar {
ToolbarItem(placement:.automatic) {
HStack{
Button("top"){
position = 1
}
Button("mid"){
position = 2
}
Button("end"){
position = 3
}
}
}
}
}
}
}
struct ScrollItem:Identifiable{
var id = UUID()
var title:String
static func items(_ count:Int) -> [ScrollItem]{
var result:[ScrollItem] = []
for i in 0..<count{
result.append(ScrollItem(title:String("index:\(i) title:\(Int.random(in: 1000...5000))")))
}
return result
}
}
遗憾
没有简单的手段记录当前的滚动位置。