avaloniaProject/ViewModels/CalculatorViewModel.cs

using Avalonia.Controls;
using avaloniaPr.Models;
using ReactiveUI;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace avaloniaPr.ViewModels
{
    public class CalculatorViewModel : ViewModelBase
    {
        string textCalculator = "Выберите арифметическую операцию:";
        string textButton = "Вычислить";
        string selectItem = "";
        double result;
        double oneNum;
        double twoNum;

        public string TextCalculator
        {
            get => textCalculator;
            set => this.RaiseAndSetIfChanged(ref textCalculator, value);
        }
        public string TextButton
        {
            get => textButton;
            set => this.RaiseAndSetIfChanged(ref textButton, value);
        }
        public List<string> ListItem
        {
            get => Models.ItemsOperation.Items;
        }
        public string SV
        {
            get => selectItem;
            set
            {
                if (value == "Сумма")
                {
                    this.RaiseAndSetIfChanged(ref selectItem, "+");
                }
                else if (value == "Разность")
                {
                    this.RaiseAndSetIfChanged(ref selectItem, "-");
                }
                else if (value == "Умножение")
                {
                    this.RaiseAndSetIfChanged(ref selectItem, "*");
                }
                else if (value == "Деление")
                {
                    this.RaiseAndSetIfChanged(ref selectItem, "/");
                }
            }
        }
        public double OneNum
        {
            get => oneNum;
            set
            {
                this.RaiseAndSetIfChanged(ref oneNum, value);
            }
        }
        public double TwoNum
        {
            get => twoNum;
            set
            {
                this.RaiseAndSetIfChanged(ref twoNum, value);
            }
        }
        public void CommandCalculator()
        {
            switch (SV) 
            {
                case "+":
                    {
                        result = OneNum + TwoNum;
                        Result++;
                        Result--;
                    }
                    break;
                case "-":
                    {
                        result = OneNum - TwoNum;
                        Result++;
                        Result--;
                    }
                    break;
                case "*":
                    {
                        result = OneNum * TwoNum;
                        Result++;
                        Result--;
                    }
                    break;
                case "/":
                    {
                        result = OneNum / TwoNum;
                        Result++;
                        Result--;
                    }
                    break;
            }
        }
        public double Result
        {
            get => result;
            set
            {
                this.RaiseAndSetIfChanged(ref result, value);
            }
        }
    }
}