.NET Tips and Tricks -Learn how Visual Studio implements intellisense for Web Forms

Learn how Visual Studio implements intellisense for Web Forms

In case you don't know, Visual Studio .NET uses XSD schemas to provide intellisense processing for the Web Forms HTML-View architecture. Some common schemas can be found in the following directories:

C:\Program Files\Microsoft Visual Studio .NET\Common7\Packages\schemas\html

Here are the schemas that can be found here:

ie3_2nav3_0.xsd - This schema includes defintions for Netscape Navigator 3.0 and Internet Explorer 3.2 markup.
nav4_0.xsd -This schema includes definitions for Netscape Navigator 4.0 markup.
ie5_0.xsd -This schema, which will probably be used more than any other, supports Internet Explorer 5.0 or later, as of now.

C:\Program Files\Microsoft Visual Studio .NET\Common7\Packages\schemas\xml

AddRotator.xsd - This is not an intellisense schema, but rather contains the definitions for the Advertisements XML file used by the AdRotator control.
asp.xsd - This schema contains all of the defintions for all ASP.NET server controls. Some of the attributes and elements contained are tagged with VS.NET tags to further extend intellisense support, such as displaying a color picker when setting a color attribute.
MobilePage.xsd - This schema defines a MobilePage, provided by the Mobile Internet Toolkit.
MobileForm.xsd - This schema defines a MobileForm, which must be added to a MobilePage. This schema also contains the defintions for the Mobile controls.
MobileUserControl.xsd - This schema contains defintions for implementing a Mobile User Controls. Mobile controls can be added to a Mobile user control.
MobileHtml32Template.xsd - This schema contains the defintions for HTML elements and attributes that are supported by Mobile Web Forms.
MobileChtmlTemplate.xsd - This schema contains the defintions for cHTML elements and attributes that are supported by Mobile Web Forms.
tdlschema.xsd - This schema is used by Visual Studio .NET for supporting enterprise templates. Enterprise templates are available with the Enterprise versions of Visual Studio .NET.
wshmeta.xsd - This schema contains definitions for the Windows Script Host.
xsdschema.xsd - This schema contains the definitions for the XSD schema.

Of the schemas listed above, we will only examine one, asp.xsd, as well as create new one for a custom ASP.NET control. For each ASP.NET server control available, there is a corresponding <xsd:element> definition in the schema; and for each property of a control, there is a corresponding <xsd:attribute> element.

Note: The above statement is not entirely correct, because some complex properties, such as collections, are also nested as elements.

Here is the schema defintion for an ASP.NET Button control:

<!-- <asp:Button> -->
<xsd:complexType name="ButtonDef" vs:noambientcontentmodel="true">
  <xsd:attribute name="CommandArgument" type="xsd:string" />
  <xsd:attribute name="CausesValidation" type="xsd:boolean" />
  <xsd:attribute name="Text" type="xsd:string" />
  <xsd:attribute name="CommandName" type="xsd:string" />
  <xsd:attribute name="OnCommand" vs:omtype="event" />
  <xsd:attribute name="OnClick" vs:omtype="event" />
  <xsd:attribute name="Enabled" type="xsd:boolean" />
  <xsd:attribute name="BorderWidth" type="ui4" />
  <xsd:attribute name="BorderColor" type="xsd:string" vs:builder="color" />
  <xsd:attribute name="BorderStyle" type="BorderStyle" />
  <xsd:attributeGroup ref="WebControlAttributes" />
</xsd:complexType>

The <xsd:complexType> tag defines a Button type. Therefore, anywhere through the schema document, <xsd:element> tags can be defined that are of type ButtonDef:

  <!-- valid top-level elements -->
  <xsd:element name="AdRotator" type="AdRotatorDef" />
  <xsd:element name="Label" type="LabelDef" />
  <xsd:element name="Button" type="ButtonDef" />

All <xsd:attribute> tags correspond with the properties of a Button control. The syntax is <xsd:attribute name="$name" type="$type" />, where $name represents the property name and $type represents the property's type. Note that these types do not have to match exactly with what the true types for the properties are. These types are simply used by schema validation and intellisense to validate values you set. Some of the attributes also have vs:attribute="value" markup. This vs attribute is a tag prefix for the Visual Studio .NET intellisense namespace, http://schemas.microsoft.com/Visual-Studio-Intellisense. Don't try to navigate to this link using a web browser; the norm for XML namespaces is to use URLs, since they are almost guaranteed to be unique. During schema processing, VS.NET searches everything that has a VS.NET namespace attribute applied, and performs processing based on the attribute name and value. Some common VS.NET markup is shown below:

Common VS.NET Intellisense Schema Annotations

Annotation

Used For

Valid Values

vs:builder

Specifies the builder to be used for editing a property's value. Builders are analagous to UITypeEditors in design-mode.

style, url, color

vs:friendlyname

Specifies the display name for the schema. This name is used in the TargetSchema property of the DOCUMENT, as well as in the Properties dialog of HTML and ASP.NET pages.

(any)

vs:iscasesensitive

Specifies whether the tags in the ASP.NET page are case-sensitive.

true, false

vs:ishtmlschema

Used at the root level and specifies whether the schema is an HTML document schema.

true, false

vs:nonbrowseable

Specifies that the attribute will not appear in statement completion in HTML View.

true, false

vs:readonly

Specifies that the attribute can not be modified in the Properties window in HTML View.

true, false

vs:requireattributequotes

Specifies that the attribute values in the ASP.NET page must have quotes when used in HTML View.

true, false

The MSDN documentation provides a complete set of the Visual Studio .NET schema annotations.

A Custom Control With Intellisense Support

To implement intellisense support for a control other than one of the ASP.NET controls or Mobile controls, you must provide your own schema for the control's defintion. A good thing to do is to use an Intellisense Generator, such as the one found in the Product's section of www.bluevisionsoftware.com. But for starters, you will simply create a new XSD schema and place it in the same directory as the asp.xsd schema. Once there, with all the defintions necessary, you need to apply the schema to the web form onto which your control will be placed. This is done by adding an xmlns atttribute to the <body> element, similar to what is done on a Mobile Web Forms page to enable intellisense support for Mobile controls. Here is the syntax:

<body xmlns:bv="urn:http://schemas.bluevisionsoftware.com/AspNet/WebControls">

The syntax above assumes that your custom controls will have a tag prefix of bv. Then, in HTML view of the page, you can add your custom controls, which will then be fully supported by the VS.NET Intellisense engine.

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