Source code for CodeSlicing episode on debouncing user input in a property wrapper

DebounceStatePropertyWrapperDemo.swift

//
//  DebounceStatePropertyWrapperDemo.swift
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
//  of the Software, and to permit persons to whom the Software is furnished to do so,
//  subject to the following conditions:
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
//  INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
//  PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
//  COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
//  AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
//  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//
//  Copyright © 2022 Adam Fordyce. All rights reserved.
//

import SwiftUI
import PureSwiftUI
import Combine

@propertyWrapper
private struct DebouncedState<Value>: DynamicProperty {

    @StateObject private var backingState: BackingState
    
    init(wrappedValue: Value, delay: Double = 0.3) {
        self.init(initialValue: wrappedValue, delay: delay)
    }
    
    init(initialValue: Value, delay: Double = 0.3) {
        _backingState = StateObject(wrappedValue: BackingState(initialValue: initialValue, delay: delay))
    }
    
    var wrappedValue: Value {
        get {
            backingState.debouncedValue
        }
        nonmutating set {
            backingState.currentValue = newValue
        }
    }
    
    var projectedValue: Binding<Value> {
        $backingState.currentValue
    }
    
    private class BackingState: ObservableObject {
        
        @Published var currentValue: Value
        @Published var debouncedValue: Value

        init(initialValue: Value, delay: Double) {
            _currentValue = Published(initialValue: initialValue)
            _debouncedValue = Published(initialValue: initialValue)
            $currentValue
                .debounce(for: .seconds(delay), scheduler: RunLoop.main)
                .assign(to: &$debouncedValue)
        }
    }
}

struct DebounceStatePropertyWrapperDemo: View {
    
    @DebouncedState(delay: 0.5) private var filterText = ""
    @State private var counter = 0
    
    var body: some View {
        VStack(alignment: .leading) {
            Text("Input text:")
            TextEditor(text: $filterText)
                .textEditorStyle()
            
            Text("Debounced text:")
                .padding(.top, 15)
            Text(filterText)
                .textOutputStyle()
            
            ZStack {
                Text("\(counter)")
                    .customFont(50, .light)
            }
            .frame(100)
            .clipCircleWithStroke(.gray, lineWidth: 1, fill: .white)
            .greedyWidth()
            .yOffset(100)
        }
        .padding()
        .onChange(of: filterText) { newValue in
            counter += 1
        }
    }
}

private extension View {

    func textEditorStyle() -> some View {
        height(100)
        .textBoxBorder()
    }

    func textOutputStyle() -> some View {
        padding(5)
        .height(100, .top)
        .greedyWidth(.leading)
        .background(.white)
        .textBoxBorder()
    }

    func textBoxBorder() -> some View {
        clipRoundedRectangleWithStroke(5, .gray, lineWidth: 1)
    }
}

struct DebounceStatePropertyWrapperDemo_Previews: PreviewProvider {
    struct DebounceStatePropertyWrapperDemo_Harness: View {

        var body: some View {
            DebounceStatePropertyWrapperDemo()
                .greedyFrame()
                .background(LinearGradient([.white(0.8), .white(0.5)], to: .bottomTrailing))
                .ignoresSafeArea()
        }
    }

    static var previews: some View {
        DebounceStatePropertyWrapperDemo_Harness()
            .previewDevice(.iPhone_13_Pro_Max)
    }
}