Regular Expression Validation Custom Field Type

I have been reading Todd Bleekers book Developers Guide To Windows SharePoint Services 3.0 and came across a great implementation in creating a custom field type in WSS 3.0. This custom field type is a Regular Expression Validation Custom Field Type. I love this implementation as it can be used for many situations…anywhere you want to validate input using regular expressions.

• Emails
  

• Telephone numbers
  

• Address
  

• Numbers only
  

• Letters only
  

• Alphanumeric only
  

If you are after a regular expression to validate input then this is one of the best sites to use.

Here are a couple of screen shots that displays the objective.

A Custom Field Type is a class that is complied into an assembly, so the first thing to do is open VS.NET 2005 and create a new Class Library project.

• Provide a meaningful project name
  

• You need to add an assembly reference to Windows SharePoint Services 12.0.0.0 in the .Net project.
  

• Rename the default class Class1.cs to RegExTextField.cs. (VS.NET will refactor the project to update the related references to the new class name)
  

• Add two directives to the top of the class.
  

  • using Microsoft.SharePoint
    

  • using System.Text.RegularExpressions
    

• You need to now inherit functionality so it behaves like a CFT. There are many different CFT classes you can inherit from to get different behaviour, but we want to inherit the SPFiledText as this most resembles our CFT. So the declaration will look like the following
  

  • public class RegExTextField : SPFieldText
    

• WSS v3 will call into one of two constructors so the class must implement both of them even though they don’t implement any code.
  

  • public RegExTextField(SPFieldCollection fields, string fieldName)
    : base(fields, fieldName)
    { }
    

  • public RegExTextField(SPFieldCollection fields, string typeName, string displayName)
    : base(fields, typeName, displayName)
    { }
    

• The GetValidatedString method converts the field type value into a validated serialised string. We can use this method to create our own custom validation from the value entered. Insert this after the second constructor.
  

  public override string GetValidatedString(object value)
  {
      string textValue = value.ToString();
  

    //Only compare RegEx if a value is present
    if (textValue.Length > 0)
    {
        //setup regex based on custom property
        Regex reg = new Regex(GetCustomProperty(“RegularExpression”).ToString(), RegexOptions.IgnoreCase);

        //if the value entered does not match
        if (!reg.IsMatch(textValue))
        {
            throw new SPFieldValidationException(GetCustomProperty(“ExceptionMessage”).ToString());
        }
        else
        {
            return textValue;
        }
    }
    else
    {
        return textValue;
    }
}

• Sign the assembly so it can be deployed to the GAC. You can sign the assembly by navigating to the Class Library project properties and click the Signing tab. Build the project to produce the assembly and deploy to the GAC.
  

Now you need to define what elements you want displayed when the CFT is used in the Create Column and Additional Columns Settings.

• In the same Class Library project choose Add àNew Item and select XML File.
  
• In the Name field type fldtypes_RegExTextField.xml. (The name of the file is important as CFTs must begin with fldtypes)
  
• Add the following code to your .xml file
  

  <?xml version=”1.0″ encoding=”utf-8″ ?>
  <FieldTypes>
      <FieldType>
          <Field Name=”TypeName”>RegExTextField</Field>
          <Field Name=”ParentType”>Text</Field>
          <Field Name=”TypeDisplayName”>
              Single line of text (with RegEx validation)
          </Field>
          <Field Name=”FieldTypeClass”>
              CustomFieldTypes.RegExValidation.RegExTextField,
              CustomFieldTypes.RegExValidation, Version=1.0.0.0,
              Culture=neutral, PublicKeyToken=d7f772d26282eb60
          </Field>
          <PropertySchema>
              <Fields>
                  <Field Name=”RegularExpression” DisplayName=”Regular Expression” MaxLength=”255″ DisplaySize=”35″ Type=”Text”>
                      <Default></Default>
                  </Field>
                  <Field Name=”ExceptionMessage” DisplayName=”Exception Message” MaxLength=”255″ DisplaySize=”35″ Type=”Text”>
                      <Default></Default>
                  </Field>
              </Fields>
          </PropertySchema>
      </FieldType>
  </FieldTypes> 

  • The FieldType elements define the attributes associated with the CFT when it appears in the Name and Type section of the Create Column page.
    
  • The PropertySchema elements define the attributes associated when it appears in the Additional Column Settings (after you select the CFT radio button)
    

  

• CFT have two scopes, Farm or List.
  
  • Farm: fldtypes*.xml files reside in the ..\12\Template\XML folder.
    
  • List: The schema.xml file that defines a list template can include CFTs.
    
• Because this CFT will be useful across the farm we will copy it to the ..\12\Template\XML folder In Windows Explorer copy the fldtypes_RegExTextField.xml to ..\12\Template\XML.
  
• Now all you have to do is perform an application pool recycle, then go to any WSS 3.0 list and add a new column and you will see your CFT.
  

Now you can use your new WSS 3.0 RegEx Validation CFT in many situations.