Validates and converts the field value into a serialized form.
Assembly: Microsoft.SharePoint (in Microsoft.SharePoint.dll)
Available in Sandboxed Solutions: Yes
Available in SharePoint Online
This method is used for data serialization logic and for field validation logic that is specific to a custom field type.
In a custom type-specific class, override this method to define the following kinds of logic:
Data-validation; for example, to throw an exception in server-side code if the field is required.
Pre-update data processing; for example, to filter out bad data but not fail validation.
Serialization; for example, to convert a field value object into string format.