SwiftUI View.onChange(of:perform:) reimplementation for iOS 13

ViewOnChangeValue.swift

import SwiftUI

private struct ViewOnChangeValueObserver<Content: View, Value: Equatable>: View {
    let content: Content
    let value: Value
    let action: (Value) -> Void

    @State private var oldValue: Value

    init(
        value: Value,
        action: @escaping (Value) -> Void,
        content: Content
    ) {
        self.value = value
        self.action = action
        self.content = content
        self._oldValue = State(initialValue: value)
    }

    var body: some View {
        if oldValue != value {
            DispatchQueue.main.async {
                oldValue = value
                action(value)
            }
        }
        return content
    }
}

extension View {
    func onChangeValue<Value>(
        of value: Value,
        perform action: @escaping (Value) -> Void
    ) -> some View where Value: Equatable {
        ViewOnChangeValueObserver(value: value, action: action, content: self)
    }
}