SwiftUI - Restricting drag of a rectangle inside a view

Question

Below is the code I wrote for dragging a rectangle. I would like to restrict its dragging to be within the border of the view given. ie if the user tries to move the rectangle outside the border of the view, it should stay within the border edges. I tried using GeometryReader to get the rect of both the rectangle and the outer view, but I am unable to restrict the drag. Please help.

import SwiftUI

struct DragView: View {
    @State private var currentPosition: CGSize = .zero
    @State private var newPosition: CGSize = .zero
    @State private var parentRect: CGRect = .zero
    @State private var childRect: CGRect = .zero

    var body: some View {
            VStack {
                Rectangle().frame(width: 100, height: 100, alignment: .top)
                    .foregroundColor(.blue)
                    .offset(x: self.currentPosition.width, y: self.currentPosition.height)
                    .background(GeometryGetter(rect: $childRect))

                .gesture(
                    DragGesture(minimumDistance: 0, coordinateSpace: .global)
                        .onChanged { value in
                            self.currentPosition = CGSize(width: value.translation.width + self.newPosition.width, height: value.translation.height + self.newPosition.height)
                        }
                        .onEnded { value in
                            self.currentPosition = CGSize(width: value.translation.width + self.newPosition.width, height: value.translation.height + self.newPosition.height)
                            self.newPosition = self.currentPosition
                        }
                )
            }
            .frame(width: 300, height: 500, alignment: .center)
            .border(Color.black, width: 1)
            .background(GeometryGetter(rect: $parentRect))
    }
}

struct GeometryGetter: View {
    @Binding var rect: CGRect

    var body: some View {
        GeometryReader { geometry in
            Group { () -> AnyView in
                DispatchQueue.main.async {
                    self.rect = geometry.frame(in: .global)
                }
                return AnyView(Color.clear)
            }
        }
    }
}

Chris · Accepted Answer · 2020-04-01 16:41:24Z

check this out:

struct ContentView: View {
    @State private var currentPosition: CGSize = .zero
    @State private var newPosition: CGSize = .zero
    @State private var parentRect: CGRect = .zero
    @State private var childRect: CGRect = .zero

    func correctPostion() {
        print(self.currentPosition)
        if self.currentPosition.width > 100 {
            self.currentPosition.width = 100
        }
        if self.currentPosition.height > 200 {
            self.currentPosition.height = 200
        }
        if self.currentPosition.width < -100 {
            self.currentPosition.width = -100
        }
        if self.currentPosition.height < -200 {
            self.currentPosition.height = -200
        }
    }

    var body: some View {
            VStack {
                Rectangle().frame(width: 100, height: 100, alignment: .top)
                    .foregroundColor(.blue)
                    .offset(x: self.currentPosition.width, y: self.currentPosition.height)
                    .background(GeometryGetter(rect: $childRect))

                .gesture(
                    DragGesture(minimumDistance: 0, coordinateSpace: .global)
                        .onChanged { value in
                            self.currentPosition = CGSize(width: value.translation.width + self.newPosition.width, height: value.translation.height + self.newPosition.height)

                            self.correctPostion()
                        }
                        .onEnded { value in
                            self.currentPosition = CGSize(width: value.translation.width + self.newPosition.width, height: value.translation.height + self.newPosition.height)

                            self.correctPostion()

                            self.newPosition = self.currentPosition
                        }
                )
            }
            .frame(width: 300, height: 500, alignment: .center)
            .border(Color.black, width: 1)
            .background(GeometryGetter(rect: $parentRect))
    }
}

struct GeometryGetter: View {
    @Binding var rect: CGRect

    var body: some View {
        GeometryReader { geometry in
            Group { () -> AnyView in
                DispatchQueue.main.async {
                    self.rect = geometry.frame(in: .global)
                }
                return AnyView(Color.clear)
            }
        }
    }
}

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