How to create a custom field type which is inherited the "Text" field type

Question

I am using sharepoint 2010. I would like to create a custom field type in Visual Studio which is inherited the "Text" field type. I never created a custom field type. Can someone tell me how to do this?

Answer 1

You can create your custom field with Visual studio which is inherited from SPFieldText.

For sample code:

public class EmailField : SPFieldText
    {
        public EmailField(SPFieldCollection fields, string fieldName)
            : base(fields, fieldName)
        {
        }
        public EmailField(SPFieldCollection fields, string typeName, string displayName)
            : base(fields, typeName, displayName)
        {
        }
        public override BaseFieldControl FieldRenderingControl
        {
            [SharePointPermission(SecurityAction.LinkDemand, ObjectModel = true)]
            get
            {
                BaseFieldControl fieldControl = new EmailFieldControl();
                fieldControl.FieldName = this.InternalName;
                return fieldControl;
            }
        }
        public override string GetValidatedString(object value)
        {
            if ((this.Required == true) && ((value == null)|| ((String)value == "")))
            {
                throw new SPFieldValidationException(this.Title + " must have a value.");
            }
            else
            {
                Email10ValidationRule rule = new Email10ValidationRule();
                ValidationResult result = rule.Validate(value, CultureInfo.InvariantCulture);
                if (!result.IsValid)
                {
                    throw new SPFieldValidationException((String)result.ErrorContent);
                }
                else
                {
                    return base.GetValidatedString(value);
                }
            }
        }
    }
}

You can find all steps mentioned below:

http://www.c-sharpcorner.com/uploadfile/Roji.Joy/creating-a-custom-field-type-for-sharepoint-2010-email-validation-field/

http://weblogs.asp.net/sreejukg/developing-custom-field-type-for-sharepoint-2010

Answer 2

You need to override the SPFieldText Class.

Add the required constructors.

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

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

Now you need to override the class in which you are providing your field's functionality.

Details could be found here.