ProgrammaticScrollView

ProgrammaticScrollView.swift

import SwiftUI
import Foundation
struct ProgrammaticScrollView<Content: View>: View {
  @Binding private var scrollID: Int?
  let content: () -> Content
  init(scrollID: Binding<Int?>, @ViewBuilder content: @escaping () -> Content) {
    self._scrollID = scrollID
    self.content = content
  }
  
  var body: some View {
    ScrollView {
      content()
        .padding(.horizontal)
        .background {
          VStack {
            ForEach(1..<101) { num in
              VStack {
                Text("\(num)").frame(maxWidth: .infinity, alignment: .leading)
                  .id(num)
                  .opacity(0.0)
                Spacer()
              }
            }
          }
        }
    }
    .scrollPosition(id: $scrollID, anchor: .top)
    .animation(.default, value: self.scrollID)
    
    .task(id: "autoscroll") {
      scrollID = 1
      await scroll(by: 1, every: .seconds(1))
    }
    .safeAreaInset(edge: .bottom) {
      if scrollID != 1 {
        Button("Scroll to top", systemImage: "arrow.up") {
          scrollID = 1
        }
        .containerRelativeFrame(.horizontal, alignment: .leading)
        .labelStyle(.iconOnly)
        .buttonStyle(CircleButton(background: .blue))
        .padding(.leading)
      }
      
      if scrollID != 100 {
        Button("Scroll to bottom", systemImage: "arrow.down") {
          scrollID = 100
        }
        .containerRelativeFrame(.horizontal, alignment: .trailing)
        .labelStyle(.iconOnly)
        .buttonStyle(CircleButton(background: .blue))
        .padding(.trailing)
      }
    }
    
  }
  
  // this function demonstrates how your model can scroll the view to any position it wants at any time.
  @MainActor
  func scroll(by percentage: Int, every duration: ContinuousClock.Instant.Duration) async {
    while true {
      guard let oldValue = scrollID else { scrollID = 0; continue }
      switch oldValue {
        case Int.min..<0: scrollID = 0
        case 0..<100: scrollID = oldValue + percentage
        case 100..<Int.max: scrollID = 100
        default: scrollID = 0
      }
      _ = try? await Task.sleep(for: duration)
    }
  }
}

struct CircleButton<Background: ShapeStyle>: ButtonStyle {
  let background: Background
  
  func makeBody(configuration: Configuration) -> some View {
    configuration.label
      .padding()
      .background(background, in: .circle)
  }
}

struct ExampleView: View {
  @State private var scrollPercentage: Int? = 1
  @State private var picker = 34
  var body: some View {
    ProgrammaticScrollView(scrollID: $scrollPercentage) {
      Text(verbatim: whosOnFirst)
    }
      .safeAreaInset(edge: .bottom) {
        bottomBar
      }
  }
  
  @ViewBuilder var bottomBar: some View {
    VStack {
      HStack {
        Picker("Select a number", selection: $picker) {
          ForEach(0..<100) { num in
            Text("\(num)").id(num)
          }
        }
        Button("Scroll to \(picker)%") { scrollPercentage = picker }
      }
      LabeledContent("scrollPercentage", value: "\(scrollPercentage)") // useful for debugging
    }
    .padding(.horizontal)
    .background(.thinMaterial, ignoresSafeAreaEdges: .bottom)
  }
}

#Preview {
  ExampleView()
}

let whosOnFirst = """
“WHO'S ON FIRST?”
The text of Abbott & Costello's classic routine.
Abbott: Well, Costello, I'm going to New York with you. Bucky Harris the Yankee's manager gave me a job as
coach for as long as you're on the team.
Costello: Look Abbott, if you're the coach, you must know all the players.
Abbott: I certainly do.
Costello: Well you know I've never met the guys. So you'll have to tell me their names, and then I'll know who's
playing on the team.
Abbott: Oh, I'll tell you their names, but you know it seems to me they give these ball players now-a-days very
peculiar names.
Costello: You mean funny names?
Abbott: Strange names, pet names...like Dizzy Dean...
Costello: His brother Daffy
Abbott: Daffy Dean...
Costello: And their French cousin.
Abbott: French?
Costello: Goofe'
Abbott: Goofe' Dean. Well, let's see, we have on the bags, Who's on first, What's on second, I Don't Know is on
third...
Costello: That's what I want to find out.
Abbott: I say Who's on first, What's on second, I Don't Know's on third.
Costello: Are you the manager?
Abbott: Yes.
Costello: You gonna be the coach too?
Abbott: Yes.
Costello: And you don't know the fellows' names.
Abbott: Well I should.
Costello: Well then who's on first?
Abbott: Yes.
Costello: I mean the fellow's name.
Abbott: Who.
Costello: The guy on first.
Abbott: Who.
Costello: The first baseman.
Abbott: Who.
Costello: The guy playing...
Abbott: Who is on first!
Costello: I'm asking you who's on first.
Abbott: That's the man's name.
Costello: That's who's name?
Abbott: Yes.
Costello: Well go ahead and tell me.
Abbott: That's it.
Costello: That's who?
Abbott: Yes. PAUSE
Costello: Look, you gotta first baseman?
Abbott: Certainly.
Costello: Who's playing first?
Abbott: That's right.
Costello: When you pay off the first baseman every month, who gets the money?
Abbott: Every dollar of it.
Costello: All I'm trying to find out is the fellow's name on first base.
Abbott: Who.
Costello: The guy that gets...
Abbott: That's it.
Costello: Who gets the money...
Abbott: He does, every dollar of it. Sometimes his wife comes down and collects it.
Costello: Who's wife?
Abbott: Yes. PAUSE
Abbott: What's wrong with that?
Costello: I wanna know is when you sign up the first baseman, how does he sign his name?
Abbott: Who.
Costello: The guy.
Abbott: Who.
Costello: How does he sign...
Abbott: That's how he signs it.
Costello: Who?
Abbott: Yes. PAUSE
Costello: All I'm trying to find out is what's the guys name on first base.
Abbott: No. What is on second base.
Costello: I'm not asking you who's on second.
Abbott: Who's on first.
Costello: One base at a time!
Abbott: Well, don't change the players around.
Costello: I'm not changing nobody!
Abbott: Take it easy, buddy.
Costello: I'm only asking you, who's the guy on first base?
Abbott: That's right.
Costello: OK.
Abbott: Alright. PAUSE
Costello: What's the guy's name on first base?
Abbott: No. What is on second.
Costello: I'm not asking you who's on second.
Abbott: Who's on first.
Costello: I don't know.
Abbott: He's on third, we're not talking about him.
Costello: Now how did I get on third base?
Abbott: Why you mentioned his name.
Costello: If I mentioned the third baseman's name, who did I say is playing third?
Abbott: No. Who's playing first.
Costello: What's on base?
Abbott: What's on second.
Costello: I don't know.
Abbott: He's on third.
Costello: There I go, back on third again! PAUSE
Costello: Would you just stay on third base and don't go off it.
Abbott: Alright, what do you want to know?
Costello: Now who's playing third base?
Abbott: Why do you insist on putting Who on third base?
Costello: What am I putting on third.
Abbott: No. What is on second.
Costello: You don't want who on second?
Abbott: Who is on first.
Costello: I don't know. Together: Third base! PAUSE
Costello: Look, you gotta outfield?
Abbott: Sure.
Costello: The left fielder's name?
Abbott: Why.
Costello: I just thought I'd ask you.
Abbott: Well, I just thought I'd tell ya.
Costello: Then tell me who's playing left field.
Abbott: Who's playing first.
Costello: I'm not...stay out of the infield!!! I want to know what's the guy's name in left field?
Abbott: No, What is on second.
Costello: I'm not asking you who's on second.
Abbott: Who's on first!
Costello: I don't know. Together: Third base! PAUSE
Costello: The left fielder's name?
Abbott: Why.
Costello: Because!
Abbott: Oh, he's center field. PAUSE
Costello: Look, You gotta pitcher on this team?
Abbott: Sure.
Costello: The pitcher's name?
Abbott: Tomorrow.
Costello: You don't want to tell me today?
Abbott: I'm telling you now.
Costello: Then go ahead.
Abbott: Tomorrow!
Costello: What time?
Abbott: What time what?
Costello: What time tomorrow are you gonna tell me who's pitching?
Abbott: Now listen. Who is not pitching.
Costello: I'll break you're arm if you say who's on first!!! I want to know what's the pitcher's name?
Abbott: What's on second.
Costello: I don't know. Together: Third base! PAUSE
Costello: Gotta a catcher?
Abbott: Certainly.
Costello: The catcher's name?
Abbott: Today.
Costello: Today, and tomorrow's pitching.
Abbott: Now you've got it.
Costello: All we got is a couple of days on the team. PAUSE
Costello: You know I'm a catcher too.
Abbott: So they tell me.
Costello: I get behind the plate to do some fancy catching, Tomorrow's pitching on my team and a heavy hitter
gets up. Now the heavy hitter bunts the ball. When he bunts the ball, me, being a good catcher, I'm gonna throw
the guy out at first. So I pick up the ball and throw it to who?
Abbott: Now that's the first thing you've said right.
Costello: I don't even know what I'm talking about! PAUSE
Abbott: That's all you have to do.
Costello: Is to throw the ball to first base.
Abbott: Yes!
Costello: Now who's got it?
Abbott: Naturally. PAUSE
Costello: Look, if I throw the ball to first base, somebody's gotta get it. Now who has it?
Abbott: Naturally.
Costello: Who?
Abbott: Naturally.
Costello: Naturally?
Abbott: Naturally.
Costello: So I pick up the ball and I throw it to Naturally.
Abbott: No you don't you throw the ball to Who.
Costello: Naturally.
Abbott: That's different.
Costello: That's what I said.
Abbott: you're not saying it...
Costello: I throw the ball to Naturally.
Abbott: You throw it to Who.
Costello: Naturally.
Abbott: That's it.
Costello: That's what I said!
Abbott: You ask me.
Costello: I throw the ball to who?
Abbott: Naturally.
Costello: Now you ask me.
Abbott: You throw the ball to Who?
Costello: Naturally.
Abbott: That's it.
Costello: Same as you! Same as YOU!!! I throw the ball to who. Whoever it is drops the ball and the guy runs to
second. Who picks up the ball and throws it to What. What throws it to I Don't Know. I Don't Know throws it back
to Tomorrow, Triple play. Another guy gets up and hits a long fly ball to Because. Why? I don't know! He's on third
and I don't give a darn!
Abbott: What?
Costello: I said I don't give a darn!
Abbott: Oh, that's our shortstop.
Costello: (makes screaming sound)
"""