Thread Task

//This example requires the 'Xamarin.Android GUI' option to be enabled
//This is a calculator using Mono.CSharp.Evaluator to evaluate expressions

//+ref=Mono.CSharp.dll
using System;
using System.Text.RegularExpressions;
using System.IO;
using Mono.CSharp;
using Android.Widget;
using Android.Content;
using Android.Views.InputMethods;
using System.Threading.Tasks;
using NativeUiLib; //This adds the UI controls

namespace CSharp_Shell
{

    public static class Program
    {
        static Evaluator evaluator;
        static StringWriter sw; //Results and errors are printed here
        static string evalCodeStart = "public static class Calc { public static void Eval(){ result=";
        static EditText txtDisplay; //calculator display/result line
        static TextView lblError; //calculator evaluation error line
        static LinearLayout layNumpad;
        static LinearLayout layArithmetics;

        public static void Main()
        {
           var layMain = new LinearLayout(); //Primary layout
           layMain.Orientation = Orientation.Vertical;
           txtDisplay = layMain.AddEditText(true);
           txtDisplay.Click += txtDisplay_Click;
           lblError = layMain.AddTextView(true);
           var hpx = Ui.Context.Resources.DisplayMetrics.HeightPixels * 0.1;
           txtDisplay.SetMinHeight((int)hpx);


           var layHor = new LinearLayout(); //This layout will contains 2 others
           layHor.Orientation = Orientation.Horizontal;
           layMain.AddView(layHor); //Add to primary layout

           layNumpad = GenerateNumpad();
           layArithmetics = GenerateArithmetics();

           layHor.AddView(layNumpad);
           layHor.AddView(layArithmetics);


           //Set layNumpad and layArithmetics to take up a specific percantage of space
           var np= new LinearLayout.LayoutParams(0, LinearLayout.LayoutParams.WrapContent);
           np.Weight = 0.85f;//Take up 85% of parent layout (parent layout is width=fill_parent)
           layNumpad.LayoutParameters = np;

           var ap= new LinearLayout.LayoutParams(0, LinearLayout.LayoutParams.WrapContent);
           ap.Weight = 0.25f; //Take up 25% of parent layout
           layArithmetics.LayoutParameters = ap;


           layMain.Show(); //Show primary layout
           txtDisplay_Click(null, null);//Hide keyboard popup

        }

        //Hide the keyboard on click
        private static async void txtDisplay_Click(object sender, EventArgs args)
        {
            var im = ((InputMethodManager)Ui.Context.GetSystemService(Context.InputMethodService));
            await Task.Delay(10); //Hiding keyboard doesn't work without a delay
            im.HideSoftInputFromWindow(txtDisplay.WindowToken, Android.Views.InputMethods.HideSoftInputFlags.None);
        }

        private static LinearLayout GenerateNumpad()
        {
            //This layout is basically a table with 6 rows and 3 columns
            var linNum = new LinearLayout();
            linNum.Orientation = Orientation.Vertical;

            var linRow1 = new LinearLayout();
            linRow1.Orientation = Orientation.Horizontal;
            linRow1.AddView(NewCalcButton("1"));
            linRow1.AddView(NewCalcButton("2"));
            linRow1.AddView(NewCalcButton("3"));

            var linRow2 = new LinearLayout();
            linRow2.Orientation = Orientation.Horizontal;
            linRow2.AddView(NewCalcButton("4"));
            linRow2.AddView(NewCalcButton("5"));
            linRow2.AddView(NewCalcButton("6"));

            var linRow3 = new LinearLayout();
            linRow3.Orientation = Orientation.Horizontal;
            linRow3.AddView(NewCalcButton("7"));
            linRow3.AddView(NewCalcButton("8"));
            linRow3.AddView(NewCalcButton("9"));

            var linRow4 = new LinearLayout();
            linRow4.Orientation = Orientation.Horizontal;
            linRow4.AddView(NewCalcButton("0"));
            linRow4.AddView(NewCalcButton("."));
            linRow4.AddView(NewCalcButton("="));

            var linRow5 = new LinearLayout();
            linRow5.Orientation = Orientation.Horizontal;
            linRow5.AddView(NewCalcButton("("));
            linRow5.AddView(NewCalcButton(")"));
            linRow5.AddView(NewCalcButton("%"));

            var linRow6 = new LinearLayout();
            linRow6.Orientation = Orientation.Horizontal;
            linRow6.AddView(NewCalcButton("sqrt"));
            linRow6.AddView(NewCalcButton("pow"));
            linRow6.AddView(NewCalcButton("mod"));

            linNum.AddView(linRow1);
            linNum.AddView(linRow2);
            linNum.AddView(linRow3);
            linNum.AddView(linRow4);
            linNum.AddView(linRow5);
            linNum.AddView(linRow6);

            return linNum;
        }

        private static LinearLayout GenerateArithmetics()
        {
            var linArth = new LinearLayout();
            linArth.Orientation = Orientation.Vertical;

            linArth.AddView(NewCalcButton("+"));
            linArth.AddView(NewCalcButton("-"));
            linArth.AddView(NewCalcButton("*"));
            linArth.AddView(NewCalcButton("/"));
            linArth.AddView(NewCalcButton("DEL"));
            linArth.AddView(NewCalcButton("CLR"));
            return linArth;
        }

        //Helper method for adding buttons to the calculator
        private static Button NewCalcButton(string text)
        {
           var btn = new Button();
           btn.Text = text;
           btn.Click += PerformButtonAction;
           return btn;
        }


        //Decide what to do when a button is pressed
        private static void PerformButtonAction(object sender, EventArgs args)
        {
            var btn = (Button)sender;
            if (btn.Text == "=") Task.Run(()=> Calculate(txtDisplay.Text));
            else if (btn.Text == "CLR")
            {
                txtDisplay.Text = string.Empty;
                lblError.Text=string.Empty;
            }
            else if (btn.Text == "DEL") //Remove character at cursor
            {
                if (txtDisplay.Text.Length == 0) return;
                var ind = txtDisplay.SelectionStart;
                txtDisplay.Text = txtDisplay.Text.Remove(ind - 1, 1);
                txtDisplay.SetSelection(--ind);
            }
            else
            {
                var text = btn.Text;
                var ind = txtDisplay.SelectionStart;
                if (text == "pow") text = "pow(,)";
                else if (text == "sqrt") text = "sqrt()";
                else if (text == "mod") text = "mod()";

                txtDisplay.Text = txtDisplay.Text.Insert(ind, text);
                txtDisplay.SetSelection(ind + text.Length);
            }
        }


        private static void Calculate(string expr)
        {
            try
            {
                InitEvaluator();

                //Convert shorthand pseudo-methods into real ones
                expr = expr.Split('=')[0];
                expr = expr.Replace("pow", "Math.Pow");
                expr = expr.Replace("sqrt", "Math.Sqrt");
                expr = expr.Replace("mod", "Math.Abs");

                var ok = evaluator.Run(evalCodeStart + expr + ";}}"); //Create evaluation class
                if (!ok) throw new ApplicationException(sw.ToString());
                ok = evaluator.Run("Calc.Eval()"); //Start evaluatuion
                if (!ok || !string.IsNullOrWhiteSpace(sw.ToString()))
                {
                    //throw exception due to evaluation error.
                    throw new ApplicationException(sw.ToString());
                }
                //Show the result
                Ui.RunOnUiThread(()=>
                {
                  txtDisplay.Text = txtDisplay.Text.Split('=')[0] + "=" + GetEvalResult();
                  txtDisplay.SetSelection(txtDisplay.Text.Length);
                  lblError.Text = string.Empty;
                });
            }
            catch(Exception ex)
            {
                //Show the exception message
                Ui.RunOnUiThread(()=>
                {
                    lblError.Text = ex.Message;
                    if (ex.InnerException != null)
                    {
                       lblError.Text +=  ex.InnerException.Message;
                    }
                });
            }
        }

        //Get evaluator result variable and process it for display
        private static string GetEvalResult()
        {
            var errorRegex = @"\((\d*),\s*(\d*)\):(.*)";
            var res = evaluator.GetVars().Replace("object result = ", string.Empty).Trim();
            if (Regex.IsMatch(res,  errorRegex))
            {
                var offset = evalCodeStart.Length +  "using System;\nobject result;".Length;
                var matches = Regex.Matches(res, errorRegex);
                res = string.Empty;
                foreach (Match match in matches)
                {
                    var pos = int.Parse(match.Groups[2].Value) - offset;
                    var error = match.Groups[3].Value;
                    res += $"{pos}: {error}";
                }
            }

            return res;
        }

        private static void InitEvaluator()
        {
           sw = new StringWriter();
           var setting = new CompilerSettings();
           var pr = new ConsoleReportPrinter(sw);
           var ctx = new CompilerContext(setting, pr);
           evaluator = new Evaluator(ctx);

           evaluator.Run("using System;"); //We probably need this
           evaluator.Run("object result;"); //Result variable, very important.
        }
    }
}