programmatically list validation

Question

I'm looking for a way to implement programmatically vallidation for NewListItems/EditListItems.

One way I found was: to use the ListEvents and Validate on ItemAdding / ItemEditing. But instead of a clean Errormessage I just get a Server Error Page.

public override void ItemAdding(SPItemEventProperties properties)
       {
          base.ItemAdding(properties);

          if (properties.AfterProperties["a"].ToString() == properties.AfterProperties["v"].ToString())
          {
                  properties.Status = SPEventReceiverStatus.CancelWithError;
                  properties.Cancel = true;
                  properties.ErrorMessage = "Error-Message";
          }
       }

Perhabs someone has en idea how to solve this problem. Thanks a lot.

Answer 1

Perhaps you see server error because your web.config file is set up for enable debugging. Try to set <customErrors mode="On" /> and CallStack="false" and verify error message.
Some more info here (Enabling Debugging)

Answer 2

I've solved the problem by using custom fields.

http://msdn.microsoft.com/en-us/library/ms446361.aspx

So I have a custom field definition located under Layouts\XML. The Name has to start with "fldtypes_":

<FieldTypes>
  <FieldType>
    <Field Name="TypeName">TestFieldType</Field>
    <Field Name="ParentType">Text</Field>
    <Field Name="TypeDisplayName">TestCode</Field>
    <Field Name="TypeShortDescription">Test</Field>
    <Field Name="UserCreatable">TRUE</Field>
    <Field Name="FieldTypeClass">CustomFieldTypes.TestFieldType, $SharePoint.Project.AssemblyFullName$</Field>
  </FieldType>
</FieldTypes>

FieldTypeClass references a class:

public  class TestFieldType:SPFieldText
    {



        public TestFieldType(SPFieldCollection fields, string fName): base(fields, fName)
        {

        }

        public TestFieldType(SPFieldCollection fields, string tName, string dName)
            : base(fields, tName, dName)
        {

        }


        public override string DefaultValue
        {
            get
            {
                return "ttt05";
            }
        }


        public override string GetValidatedString(object value)
        {

            if (!value.ToString().StartsWith("CP"))
            {
               throw new SPFieldValidationException("Product code must start with 'CP' for Contoso Products");
            }

            if (value.ToString().Length != 6)
            {
                throw new SPFieldValidationException("Product code must be 6 characters long");
            }

           return value.ToString().ToUpper();
        }
    }

This way can be used to validate programmatically or get access to the behaviour of controls.