Basics are working

Author: Trent Guillory

SnapToScrollDemo/SnapToScrollDemo.xcodeproj/project.pbxproj

@@ -7,6 +7,7 @@
 	objects = {
 
 /* Begin PBXBuildFile section */
+		84C99CD826D99BA100C1D5C4 /* Model.swift in Sources */ = {isa = PBXBuildFile; fileRef = 84C99CD726D99BA100C1D5C4 /* Model.swift */; };
 		84D9FA3626D9753600F87EF5 /* AppDelegate.swift in Sources */ = {isa = PBXBuildFile; fileRef = 84D9FA3526D9753600F87EF5 /* AppDelegate.swift */; };
 		84D9FA3826D9753600F87EF5 /* SceneDelegate.swift in Sources */ = {isa = PBXBuildFile; fileRef = 84D9FA3726D9753600F87EF5 /* SceneDelegate.swift */; };
 		84D9FA3A26D9753600F87EF5 /* ContentView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 84D9FA3926D9753600F87EF5 /* ContentView.swift */; };
@@ -17,6 +18,7 @@
 /* End PBXBuildFile section */
 
 /* Begin PBXFileReference section */
+		84C99CD726D99BA100C1D5C4 /* Model.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Model.swift; sourceTree = "<group>"; };
 		84D9FA3226D9753600F87EF5 /* SnapToScrollDemo.app */ = {isa = PBXFileReference; explicitFileType = wrapper.application; includeInIndex = 0; path = SnapToScrollDemo.app; sourceTree = BUILT_PRODUCTS_DIR; };
 		84D9FA3526D9753600F87EF5 /* AppDelegate.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AppDelegate.swift; sourceTree = "<group>"; };
 		84D9FA3726D9753600F87EF5 /* SceneDelegate.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SceneDelegate.swift; sourceTree = "<group>"; };
@@ -65,6 +67,7 @@
 				84D9FA3526D9753600F87EF5 /* AppDelegate.swift */,
 				84D9FA3726D9753600F87EF5 /* SceneDelegate.swift */,
 				84D9FA3926D9753600F87EF5 /* ContentView.swift */,
+				84C99CD726D99BA100C1D5C4 /* Model.swift */,
 			);
 			path = Sources;
 			sourceTree = "<group>";
@@ -171,6 +174,7 @@
 				84D9FA3626D9753600F87EF5 /* AppDelegate.swift in Sources */,
 				84D9FA3826D9753600F87EF5 /* SceneDelegate.swift in Sources */,
 				84D9FA3A26D9753600F87EF5 /* ContentView.swift in Sources */,
+				84C99CD826D99BA100C1D5C4 /* Model.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};

SnapToScrollDemo/Sources/ContentView.swift

@@ -4,10 +4,29 @@ import SwiftUI
 // MARK: - ContentView
 
 struct ContentView: View {
+    
+    @State var items = [("one", UUID()), ("two", UUID()), ("three", UUID()), ("four", UUID()), ("five", UUID()), ("six", UUID())]
+    
     var body: some View {
         VStack {
-            SnapHStack()
+            
+            HStackSnap {
+                
+                ForEach(items, id: \.1) { item in
+                    
+                    Text(item.0)
+                        .font(.largeTitle)
+                        .padding()
+                        .overlay(GeometryReaderOverlay(id: item.1))
+                }
+            }
         }
+        
+        /// SnapHStack {
+        ///      customForEach { item in
+        ///
+        ///      }
+        ///      }
     }
 }
 

SnapToScrollDemo/Sources/Model.swift

@@ -0,0 +1,9 @@
+
+//
+//import Foundation
+//
+//struct Model: Identifiable {
+//
+//    var systemImage: String
+//    var
+//}

Sources/HStackSnap.swift

@@ -0,0 +1,102 @@
+import Foundation
+import SwiftUI
+
+public struct HStackSnap<Content: View>: View {
+
+    // MARK: Lifecycle
+
+    public init(@ViewBuilder content: @escaping () -> Content) {
+
+        self.content = content
+    }
+
+    // MARK: Public
+
+    public var body: some View {
+
+        GeometryReader { geometry in
+            ScrollView(.horizontal) {
+
+                HStack(content: content)
+                    .frame(maxWidth: .infinity)
+                    .offset(x: scrollOffset, y: .zero)
+            }
+            .onPreferenceChange(ContentPreferenceKey.self, perform: { preferences in
+
+                for pref in preferences {
+
+                    itemFrames[pref.id] = pref
+//                        print(pref.rect.minX)
+                }
+            })
+            .coordinateSpace(name: ContentPreferenceKey.coordinateSpace)
+            .disabled(true)
+            .gesture(
+
+                DragGesture()
+                    .onChanged { gesture in
+
+                        self.scrollOffset = gesture.translation.width + prevScrollOffset
+
+                    }.onEnded { event in
+
+//                    scrollOffset += event.translation.width
+//                    dragOffset = 0
+
+                        guard var closestFrame: ContentPreferenceData = itemFrames.first?.value else { return }
+
+                        func distanceToFrame(x: CGFloat, absolute: Bool) -> CGFloat {
+
+                            if absolute {
+                                return abs(targetOffset - x)
+                            } else {
+                                return targetOffset - x
+                            }
+                        }
+
+                        for (key, value) in itemFrames {
+
+                            let currDistance = distanceToFrame(
+                                x: closestFrame.rect.minX,
+                                absolute: true)
+                            let newDistance = distanceToFrame(x: value.rect.minX, absolute: true)
+
+                            print("~~ \(value.rect.maxX)")
+
+                            if newDistance < currDistance {
+
+                                closestFrame = value
+                            }
+                        }
+
+                        withAnimation {
+
+                            print(distanceToFrame(x: closestFrame.rect.minX, absolute: false))
+
+                            scrollOffset += distanceToFrame(
+                                x: closestFrame.rect.minX,
+                                absolute: false)
+                        }
+
+                    })
+            .onTapGesture {
+
+                scrollOffset = 0
+                prevScrollOffset = 0
+            }
+        }
+    }
+
+    // MARK: Internal
+
+    var content: () -> Content
+
+    // MARK: Private
+
+    @State private var scrollOffset: CGFloat = 0
+    @State private var prevScrollOffset: CGFloat = 0
+
+    @State private var targetOffset: CGFloat = 0
+
+    @State private var itemFrames: [UUID: ContentPreferenceData] = [:]
+}

Sources/Model/ContentPreferenceKey.swift

@@ -0,0 +1,30 @@
+import Foundation
+import SwiftUI
+
+// MARK: - ExerciseEditorCellPreferenceData
+
+struct ContentPreferenceData: Equatable {
+
+    let id: UUID
+    let rect: CGRect
+}
+
+// MARK: - ExerciseEditorCellPreferenceKey
+
+struct ContentPreferenceKey: PreferenceKey {
+
+    typealias Value = [ContentPreferenceData]
+
+    // MARK: Internal
+
+    static var defaultValue: [ContentPreferenceData] = []
+
+    static var coordinateSpace: String = "ContentPreferenceKey"
+
+    static func reduce(
+        value: inout Value,
+        nextValue: () -> Value) {
+
+            value.append(contentsOf: nextValue())
+    }
+}

Sources/SnapHStack.swift

@@ -0,0 +1,25 @@
+import Foundation
+import SwiftUI
+
+public struct GeometryReaderOverlay: View {
+
+    let id: UUID
+    
+    public init(id: UUID) {
+        
+        self.id = id
+    }
+    
+    public var body: some View {
+        
+        GeometryReader { geometry in
+            
+            Rectangle().fill(Color.blue.opacity(0.5))
+                .preference(
+                    key: ContentPreferenceKey.self,
+                    value: [ContentPreferenceData(
+                        id: id,
+                        rect: geometry.frame(in: .named(ContentPreferenceKey.coordinateSpace)))])
+        }
+    }
+}