How to Correctly Do Up an Adjustable Split View in Swiftui

How to correctly do up an adjustable split view in SwiftUI?

From what I have observed, the issue seems to be coming from the handle being repositioned while being dragged along. To counteract that I have set an inverse offset on the handle, so it stays in place. I have tried to cover up the persistent handle position as best as I can, by hiding it beneath the other views (zIndex).

I hope somebody else got a better solution to this question. For now, this is all that I have got:

import PlaygroundSupport
import SwiftUI

struct SplitView<PrimaryView: View, SecondaryView: View>: View {

    // MARK: Props

    @GestureState private var offset: CGFloat = 0
    @State private var storedOffset: CGFloat = 0

    let primaryView: PrimaryView
    let secondaryView: SecondaryView

    // MARK: Initilization

    init(
        @ViewBuilder top: @escaping () -> PrimaryView,
        @ViewBuilder bottom: @escaping () -> SecondaryView)
    {
        self.primaryView = top()
        self.secondaryView = bottom()
    }

    // MARK: Body

    var body: some View {
        GeometryReader { proxy in
            VStack(spacing: 0) {
                self.primaryView
                    .frame(height: (proxy.size.height / 2) + self.totalOffset)
                    .zIndex(1)

                self.handle
                    .gesture(
                        DragGesture()
                            .updating(self.$offset, body: { value, state, _ in
                                state = value.translation.height
                            })
                            .onEnded { value in
                                self.storedOffset += value.translation.height
                            }
                    )
                    .offset(y: -self.offset)
                    .zIndex(0)

                self.secondaryView.zIndex(1)
            }
        }
    }

    // MARK: Computed Props

    var handle: some View {
        RoundedRectangle(cornerRadius: 5)
            .frame(width: 40, height: 3)
            .foregroundColor(Color.gray)
            .padding(2)
    }

    var totalOffset: CGFloat {
        storedOffset + offset
    }
}

// MARK: - Playground

let splitView = SplitView(top: {
    Rectangle().foregroundColor(.red)
}, bottom: {
    Rectangle().foregroundColor(.green)
})

PlaygroundPage.current.setLiveView(splitView)

Just paste the code inside XCode Playground / Swift Playgrounds

If you found a way to improve my code please let me know.

Increase/Decrease the size of a view horizontally by dragging the edges of it

import SwiftUI

struct ContentView: View {
    let minWidth: CGFloat = 100
    @State var width: CGFloat?

    var body: some View {
        HStack(alignment: .center) {
            Spacer()
            RedRectangle(width: width ?? minWidth)
            Resizer()
                .gesture(
                    DragGesture()
                        .onChanged { value in
                            width = max(minWidth, width! + value.translation.width)
                        }
                )
            Spacer()
        }
        .onAppear {
            width = minWidth
        }
    }
}

struct RedRectangle: View {
    let width: CGFloat

    var body: some View {
        Rectangle()
            .fill(Color.red)
            .frame(width: width, height: 100)
    }
}

struct Resizer: View {
    var body: some View {
        Rectangle()
            .fill(Color.blue)
            .frame(width: 8, height: 75)
            .cornerRadius(10)
    }
}

How to change the height of the object by using DragGesture in SwiftUI?

The correct calculation is

.gesture(
    DragGesture()
        .onChanged { value in
            height = max(MIN_HEIGHT, height + value.translation.height)
        }
)

Also, remove the infinite width. It's invalid.

.frame(minHeight: 0, maxHeight: height)

or 

.frame(minWidth: 0, maxWidth: .infinity, minHeight: 0, maxHeight: height)

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