FarPoint Spread, "INDIRECTCELL" custom function similar with Excel "INDIRECT".

FpSpread_InDirectCell.cs

using System.Windows.Forms;
using FarPoint.CalcEngine;
using FarPoint.Win.Spread.Model;

namespace WindowsFormsApplication1 {
    public partial class Form1 : Form {
        // this is only behind code.
        // put Spread in form designer.
        // run and edit A1 cell. values appear in D3, D4 and E3 cells.

        public Form1() {
            InitializeComponent();

            var fs = fpSpread1_Sheet1.Models.Data as ICustomFunctionSupport;
            var indirect = fs.GetCustomFunction("indirectCell");
            if (indirect == null) {
                fs.AddCustomFunction(new InDirectCell(fpSpread1_Sheet1.Models.Data as DefaultSheetDataModel));
            }

            fpSpread1_Sheet1.SetFormula(3, 2, "indirectCell(ADDRESS(1,1))");
            fpSpread1_Sheet1.SetFormula(3, 3, "indirectCell(A1)");
            fpSpread1_Sheet1.SetFormula(4, 2, "indirectCell(\"A1\")");
        }
    }

    public class InDirectCell : FunctionInfo {

        DefaultSheetDataModel model;
        public InDirectCell(DefaultSheetDataModel model)
        {
            this.model = model;
        }
        public override bool IsVolatile() {
            // need accept string "A1". I don't know why.
            return true;
        }
        public override object Evaluate(object[] args) {
            if(args[0] == null) return null;

            if (args[0] is CalcReference) {
                bool? a1RefType = true;
                if (args.Length > 1) {
                    a1RefType = args[1] as bool?;
                    if (a1RefType == null) {
                        a1RefType = true;
                    }
                }
                var range = (CalcReference) args[0];
                
                return range.GetValue(range.Row, range.Column);
            }
            CellExpression expression = model.ParseFormula(0, 0, args[0].ToString()) as CellExpression;
            if (expression == null) return null;
            return model.GetValue(expression.Row, expression.Column);
        }

        public override bool AcceptsReference(int i) {
            return i == 0;
        }

        public override int MaxArgs {
            get { return 2; }
        }

        public override int MinArgs {
            get { return 1; }
        }

        public override string Name {
            get { return "INDIRECTCELL"; }
        }
    }
}

R1C1 not test yet