# Using a Required Field Validator

Learn how to use the Required Field Validator to specify that a cell requires a value in your .NET application.

## Content

You can use the required field validator to specify that the cell requires a value.
A validation error occurs if the value is not valid. You can also create an action, such as adding a backcolor to the cell, that lets the user know the value is invalid.
Use the **RequiredFieldValidator** class to create the validator. Specify a notification type such as [CellStyleNotify](/spreadnet/api/latest/online-win/FarPoint.Win.Spread/FarPoint.Win.Spread.CellStyleNotify.html). Then use the [AddValidators](/spreadnet/api/latest/online-win/FarPoint.Win.Spread/FarPoint.Win.Spread.SheetView.AddValidators.html) method to add the validator to a cell range.
The following image displays a cell with an invalid, empty value.
![Required Fill Validator](https://cdn.mescius.io/document-site-files/images/2238e618-a1fb-45a6-9ce5-9a4157bd2931/images/requiredvalid.png)

## Using Code

The following example displays the invalid color if the value is deleted from the cell.

```csharp
//Cell 1,1 requires a value
FarPoint.Win.Spread.CellStyleNotify cnotify = new FarPoint.Win.Spread.CellStyleNotify();
cnotify.InvalidCellStyle.BackColor = Color.Fuchsia;
FarPoint.Win.Spread.RequiredFieldValidator requiredv = new FarPoint.Win.Spread.RequiredFieldValidator();
requiredv.Actions.Add(cnotify);
fpSpread1.Sheets[0].AddValidators(new FarPoint.Win.Spread.Model.CellRange(1, 1, 1, 1), requiredv);
fpSpread1.Sheets[0].Cells[1, 1].Text = "Value";
```

```vbnet
'Cell 1,1 requires a value
Dim cnotify As New FarPoint.Win.Spread.CellStyleNotify()
cnotify.InvalidCellStyle.BackColor = Color.Fuchsia
Dim requiredv As New FarPoint.Win.Spread.RequiredFieldValidator()
requiredv.Actions.Add(cnotify)
fpSpread1.Sheets(0).AddValidators(New FarPoint.Win.Spread.Model.CellRange(1, 1, 1, 1), requiredv)
fpSpread1.Sheets(0).Cells(1, 1).Text = "Value"
```

## See Also

[Using a Cell Comparison Validator](/spreadnet/docs/latest/online-win/overview/spwin-devguide/spwin-interactcell/spwin-cellvalid/spwin-cellvalidation/spwin-cellcomparevalidator)
[Using a Character Format Validator](/spreadnet/docs/latest/online-win/overview/spwin-devguide/spwin-interactcell/spwin-cellvalid/spwin-cellvalidation/spwin-cellcharformatv)
[Using a String Comparison Validator](/spreadnet/docs/latest/online-win/overview/spwin-devguide/spwin-interactcell/spwin-cellvalid/spwin-cellvalidation/spwin-cellcomparestring)
[Using a Value Comparison Validator](/spreadnet/docs/latest/online-win/overview/spwin-devguide/spwin-interactcell/spwin-cellvalid/spwin-cellvalidation/spwin-cellcomparevalue)
[Using an Encoding Validator](/spreadnet/docs/latest/online-win/overview/spwin-devguide/spwin-interactcell/spwin-cellvalid/spwin-cellvalidation/spwin-cellencodingvalid)
[Using the Exclude List Validator](/spreadnet/docs/latest/online-win/overview/spwin-devguide/spwin-interactcell/spwin-cellvalid/spwin-cellvalidation/spwin-cellexcludevalidator)
[Using the Include List Validator](/spreadnet/docs/latest/online-win/overview/spwin-devguide/spwin-interactcell/spwin-cellvalid/spwin-cellvalidation/spwin-cellincludevalidate)
[Using a Pair Validator](/spreadnet/docs/latest/online-win/overview/spwin-devguide/spwin-interactcell/spwin-cellvalid/spwin-cellvalidation/spwin-cellpairvalidate)
[Using the Range Validator](/spreadnet/docs/latest/online-win/overview/spwin-devguide/spwin-interactcell/spwin-cellvalid/spwin-cellvalidation/spwin-cellrangevalidator)
[Using a Regular Expression Validator](/spreadnet/docs/latest/online-win/overview/spwin-devguide/spwin-interactcell/spwin-cellvalid/spwin-cellvalidation/spwin-cellregexpression)
[Using a Required Type Validator](/spreadnet/docs/latest/online-win/overview/spwin-devguide/spwin-interactcell/spwin-cellvalid/spwin-cellvalidation/spwin-cellrequiretypev)
[Using a Surrogate Character Validator](/spreadnet/docs/latest/online-win/overview/spwin-devguide/spwin-interactcell/spwin-cellvalid/spwin-cellvalidation/spwin-cellsurrogate)
[Using a Text Length Validator](/spreadnet/docs/latest/online-win/overview/spwin-devguide/spwin-interactcell/spwin-cellvalid/spwin-cellvalidation/spwin-celltextlvalid)