Field Templates - ASP.NET Dynamic Data - page 87

Code-behind files perform most of the work required to make the generated web pages
dynamic. In this simplest example, the template overrides the DataControl property defined
by the base class. Entity templates (see Chapter 4, “Entity Templates”) use this property
when dynamically generating entity forms, to associate each field template with a matching
Label control.
Field Value Display Format
In addition to the FieldValueString property, the FieldTemplateUserControl class also
provides another property called FieldValue , which returns the raw value object. At a
cursory glance, the FieldValue property could be used to bind the Literal control as
well. However, it is important to use the FieldValueString property as it automatically
takes into account additional display format properties when converting the raw field
value to a string:
. DataFormatString specifies a .NET format string that will be passed to the
String.Format method to convert the field value to a display string.
. NullDisplayText specifies a replacement string that will be used when the raw field
value is null.
. ConvertEmptyStringToNull is a Boolean value that determines whether an empty
string value should treated as null and if the NullDisplayText will be used as a
replacement for empty strings as well as null values. This property is true by default.
. HtmlEncode is a Boolean value that determines whether any special HTML symbols
in the raw field value, such as '<' or '>' , will be encoded using escape sequences,
such as &lt; and &gt; . This property is true by default.
Display format properties can be specified in the data model by applying the
DataTypeAttribute or the DisplayFormatAttribute to a particular column, as shown in
Listing 3.3. The DisplayFormatAttribute , applied to the OrderDate column, specifies a
long date {0:D} format string. The DataTypeAttribute , applied to the RequiredDate
column, does not have its own DataFormatString property. Instead, it offers the
DisplayFormat property, which gets a default DisplayFormatAttribute generated, based
on the specified data type. For DataType.Date, the default data format string will be a
short date {0:d} .
LISTING 3.3 Specifying Display Format Using Data Annotations
using System.ComponentModel.DataAnnotations;
namespace DataModel
{
[MetadataType (typeof(Order.Metadata))]
partial class Order
{