Customize Function

Add customize formula functions

To add customize function, use the FormulaExtension class. The following example that adds a function to make given string uppercase.

unvell.ReoGrid.Formula.FormulaExtension.CustomFunctions["myUpper"] =
  (cell, args) =>
    if (args.Length == 0)
      // this function needs at least one argument
      return null;

    return Convert.ToString(args[0]).ToUpper();

Test this function, input the formula =myUpper("hello"): 169

Press enter, the cell value will be changed to uppercase. 170

About FormulaExtension

The FormulaExtension is an interface to add extensions during formula calculation.

In the ReoGrid Extension version with scription execution feature, the formula extension can be implementated by some ReoScript features. For applications use ReoGrid standard version, the FormulaExtension interface is more simple way to make formula extension features.


The CustomFunctions property is defined as:

Dictionary<string, Func<ReoGridCell, object[], object>> CustomFunctions

Simplest function example


FormulaExtension.CustomFunctions["myFunc"] = (cell, args) => {
  // function body goes here
  return null;


FormulaExtension.CustomFunctions("myFunc") = Function(cell, args)
    ' function body goes here
    Return Nothing
End Function

Using delegate function

It's also possible to use normal delegate function rather than lambda expression. To define a function:


static object MyFunc(ReoGridCell cell, params object[] arguments)
  return null;

To make this static method available in formula as customize function:


FormulaExtension.CustomFunctions["myFunc"] = MyFunc;

Shared Function MyFunc(cell As ReoGridCell, ParamArray args As Object()) As Object
  Return Nothing
End Function

To make this shared method available in formula as customize function:

FormulaExtension.CustomFunctions("myFunc") = AddressOf MyFunc

Cell instance

The first argument is the cell instance that is the owner of the formula, this function now is called from the formula, for example:

worksheet["A1"] = "=myFunc()";

The A1 cell has a formula that calls the customize function "myFunc", the function body in .NET code defined above will be invoked, the cell argument is the "A1" cell.

static object MyFunc(ReoGridCell cell, params object[] arguments)
  MessageBox.Show(cell.Position.ToAddress());   // output: A1
  return null;

Get worksheet instance from function

By getting the property Worksheet of cell instance to get worksheet instance, as well as the workbook instance from Workbook property of worksheet instance.

FormulaExtension.CustomFunctions["myFunc"] = (cell, args) => 
  var worksheet = cell.Worksheet; 
  var workbook = worksheet.Workbook;


  return null;

Limit the function scope only available in specified workbook or worksheet:

  var worksheet = cell.Worksheet; 
  var workbook = worksheet.Workbook;

  if (workbook != myWorkbook) 
    // not in valid workbook scope
    return null;

Get function arguments

The second argument is the arguments passed from caller in formula.

FormulaExtension.CustomFunctions["myFunc"] = (cell, args) => 
  if (args.Length < 2)
    // this function requires at least two arguments
    return null;

  return null;

Data type in formula

There are various types of data used during formula calculation:

  • Number (int, long, short, float, double)
  • String (string and StringBuffer)
  • Boolean
  • DateTime
  • Object

ReoGrid always use double as the number type in formula calculation. ReoGrid performs the following conversions before value passed into functions:

  • int, long, short, float will be converted into double
  • string and StringBuffer object will be converted into string

Numeric constants

Numeric constants used in formula will be initialized as double type, for example:

worksheet["A1"] = "=myFunc(10)";

The number 10 will be parsed and stored in memory as double type. The first argument in argument array will be double type.

FormulaExtension.CustomFunctions["myFunc"] = (cell, args) => 
  if (args.Length < 1 || !(args[0] is double))
    // this function requires a double value
    return null;

Numeric variables

When the numeric value was given from a cell, it will be converted into double type. Create the following function:

FormulaExtension.CustomFunctions["myFunc"] = (cell, args) =>
  double value = (double)args[0];
  return value \* 2;

Then use it in formula:

sheet["A1"] = (int)10;
sheet["B1"] = "=myFunc(A1)";

There will no data type conversion error happen. (But be careful the argument length)

References in function

Cell reference

ReoGrid will get the value from referenced cell that is used in formula automatically, like the example of 'Numeric variables'.

Range reference

If a range literal used in formula, ReoGrid will pass RangePosition struct into function, for example:

worksheet["G2:K3"] = new object[] { 1, 2, 5, 7, 8, 10, 12, 15, 16, 19};
worksheet["L2"] = "=CountEvenNumber(G2:K3)";

There is a range reference (G2:K3) that was used in the formula, it's necessary to handle it manually inside customize function body. Following example function that counts the even numbers from given range:

FormulaExtension.CustomFunctions["CountEvenNumber"] = (cell, args) =>
  if (args.Length < 1 || !(args[0] is RangePosition))
    return null; // we need a range reference

  RangePosition range = (RangePosition)args[0];

  int count = 0;

  // iterate over cells inside a range
  cell.Worksheet.IterateCells(range, (r, c, inCell) => {
    double value;

    // try get a number from cell data
    if (ReoGridCellUtility.TryGetNumberData(inCell.Data, out value) {
      if ((value % 2) == 0) {
    // continue iterate
    return true;

  return count;

Name reference

Name to cell

If a name reference to a cell, the cell's value will be get and passed into the function automatically.

worksheet.DefineNamedRange("r1", "A1");
sheet["r1"] = (int)20;
sheet["B1"] = "=myFunc(r1)";

Name to range

If a name reference to a range used in formula, ReoGrid will find the range by the name firstly, then pass the RangePosition struct object, it could be handled like range reference.

worksheet.DefineNamedRange("evenRange", "G2:K3");
worksheet["evenRange"] = new object[] { 1, 2, 4, 6, 9, 11, 13, 14, 15, 17 };
worksheet["I2"] = "=CountEvenNumber(evenRange)";
AssertSame(worksheet["I2"], 4);

Customize name reference provider

It's possible to add constant value that is used in formula but provided by .NET program. The following example adds two names that return different two constant values:

unvell.ReoGrid.Formula.FormulaExtension.NameReferenceProvider = 
  (cell, name) =>
    if (name == "myName1")
      return 10;
    else if (name == "myName2")
      return 20;
      return null;

The NameReferenceProvider is defined as:

Func<ReoGridCell, string, object> NameReferenceProvider { get; set; }

Test the name 1, input =myName1 in cell: 171

The name returns value 10: 172

Input =myName2 in cell: 173

The name returns value 20: 174

Add mathematical constants

By using the customize name reference provider, it's also possible to add some constants such as mathematical numbers, the following code defines a constant provider:


Shared Function MathConstantProvider(cell As ReoGridCell, name As String) As Object
  Select Case (name)
    Case "PI"
      Return Math.PI

    Case "E"
      Return Math.E

    Case "MyConst"
      Return 1.23456
  End Select

  Return Nothing
End Function

Apply this name reference provider:

FormulaExtension.NameReferenceProvider = AddressOf MathConstantProvider

And use the constant in formula:

worksheet("A1") = "=MyConst"

Result: 181

Combine customize function and customize name provider

Using customize name provider in a customize function is also supported. The name will be converted into value and passed into functions.

FormulaExtension.NameReferenceProvider = (cell, name) =>
  switch (name)
    case "Pi": return Math.PI;
    case "E": return Math.E;
    default: return null;

Use the name Pi in customize function:

worksheet["D3"] = "=Div100(Pi)";
AssertSame(worksheet["D3"], Math.PI / 100);

Add ReoScript language customize function

When the ReoScript module extension is enable, ReoScript script language could be used to handle the cell's data, style, border, data formats and etc, it's similar to the VBA in Excel. ReoScript supports that make .NET extension for script language, including call .NET functions in script.

ReoGrid supports that invoke ReoScript customize extension functions:

ReoScript language extension is only available in Full release package.


Add ReoScript function in C#

Add customize function to extend control:

workbook.Srm["sqrt"] = new NativeFunctionObject("sqrt", (ctx, owner, args) =>
    if (args.Length < 1)
        return NaNValue.Value;
        return Math.Sqrt(ScriptRunningMachine.GetDoubleValue(args[0], 0));


var worksheet = workbook.CurrentWorksheet;

worksheet[2, 1] = "=sqrt(400)";


Double click on cell to view its formula: 43

Customize function can also be used in script.

Customize functions in ReoScript context

Object 'workbook' is the global object which is available in both formula and script. (same as 'window' in JavaScript) Custom Function

Run the code above once and use it in formula. Using Custom Function

Press 'enter': View Result of Custom Function

Run Script to add functions in C#

It is also possible to run the script to create ReoScript functions in C#, below is the ReoScript lambda expression used to create new function.

grid.RunScript("script.myfunc = data => '[' + data + ']';");

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