Building Dynamic Forms - ASP.NET Dynamic Data - page 370

NOTE
Remember that by using the UIHintAttribute , you add presentation logic to the busi-
ness layer of your application. Although placing business logic code in the code-behind
files of a web application clearly is undesirable as it quickly leads to code duplication
and makes automated testing difficult, combining presentation and business models is
not necessarily a bad idea. You could argue that consistently using a UIHint instead of
a DataType annotation helps to clarify your design intent in the model—a tangible
benefit. However, every time you use the UIHint annotation, more and more of the
presentation logic is mixed in with the business logic, making the model more complex.
Use this as an opportunity to stop and consider whether creating a custom page or
template for the given entity and separating the presentation logic from the business
model would make the overall design simpler and easier to maintain.
Specifying Field Template Parameters
As discussed in Chapter 10, DynamicControl can initialize custom properties of field
templates using matching attributes specified in markup. As an example, the built-in
Text_Edit field template was extended with a custom Columns property that can be used
to set the Columns property of the TextBox control it contains. If you had created a custom
entity or page template for the Employee entity, you could make the Address text box
wider and accommodate longer addresses by using the following markup:
<asp:DynamicControl runat=”server” DataField=”Address” Columns=”65” />
The UIHintAttribute also supports custom property values. They are exposed for
consumption via its ControlParameters property, which returns an IDictionary<string,
object> , and have to be specified as a sequence of names and values in the
UIHintAttribute constructor, following the hint and presentation layer parameters. It is
easier to explain this with an example; following is how you could specify the Columns
parameter for the Address property in the metadata:
[MetadataType(typeof(Metadata))]
partial class Employee
{
private abstract class Metadata
{
[UIHint(“Text”, “WebForms”, “Columns”, 65)]
public object Address { get; set; }
}
}
In this example, “ Text ” is the hint, the name of a field template; “ WebForms ” is the name
of the presentation layer for which the UIHint is intended; and “ Columns ” is the name of
the first control parameter followed by 65 , its value. The UIHintAttribute constructor has