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Exposing ASP.Net Webcontrol Attributes via Markup

   Words by CRM Consultancy

   on 24/08/2016 18:00:00

The following brief article describes how we make an attribute available in ASPX Markup, as opposed to be set in the Server Code-behind:




So if we have an existing Webcontrol that is available within the Markup:


[ParseChildren(true, "")]


[ToolboxData("<{0}:DocumentList runat=server></{0}:DocumentList>")]

public class DocumentsList : WebControl


NOTE: The ParseChildren and PersistChildren are important here, as this informs .NET to process the Markup instead our control – as well as the Markup that starts our Control.


So allowing:

<asp:DropDownList ID="documentRecordSelector" AutoPostBack="true" runat="server" Height="24px" Width="240px" OnSelectedIndexChanged="documentRecordSelector_onChange">

    <asp:ListItem Text="For Case" Value="case"></asp:ListItem>             



Over a single line statement in mark-up such as:

<asp:DropDownList ID="documentRecordSelector" AutoPostBack="true" runat="server" Height="24px" Width="240px" OnSelectedIndexChanged="documentRecordSelector_onChange" />


First of all, we need to specify our code to use the relevant supporting library, in this case System.ComponentModel:


using System.ComponentModel;


We can then view an attribute in the code for this Webcontrol:


public ListDefinition ListDefinition




             return this._listDefinition;




             this._listDefinition = value;




This attribute could be a simple attribute – such as a String, Int or Decimal.


Or could (as above) be a complex typed object.


[Category("Documents List")]


[Description("The definition for how the Document List will be presented")]



public ListDefinition ListDefinition




             return this._listDefinition;




             this._listDefinition = value;




If we are using this type of complex object, then we must ensure that the Object Type is permissible to be used as a Markup Component – so in our example above for the ListDefintion Class, checking the definition of this class:



[ParseChildren(true, "Columns")]


[ToolboxData("<{0}:ListDefinition runat=\"server\"> </{0}:ListDefinition>")]

public class ListDefinition : IListDefinition


This should then allow us to refer to the Attribute from within the Markup, as opposed to being forced to populate via the Code-behind:


ASPX Markup

<crmcs:DocumentsList ID="documentsList" runat="server" TableCssClass="simpleTable" IsClient="true" IsSupplier="false" ShowDocumentDescriptionOnly="true" Width="100%">

    <ListDefinition DefinitionType="FixdColumns" ShowImage="true" FilterMode="true" />



Allowing this way of defining the List Definition as an object-in-an-object in the Markup, rather than the traditional code-behind approach:


C# Code-behind

documentsList.ListDefinition.PrefilterColumns = "'" + SpecificDocumentCategory + "','',''";

documentsList.ListDefinition.FilterMode = true;

documentsList.ListDefinition.sScrollY = 480;


This can be useful when working on ASP.Net Webform Projects – as provides a good separation of Code-behind Business Logic vs Presentation Layer Markup; and so helps keep a tighter tiered design of our Web Application.


Which, whilst not strict separation of concerns between Business Logic and Presentation (as attributes defined in Mark-up could help drive Business Logic) it does layer our solution better and so make for more transparent easy to maintain code.


Further Reading

DesignerSerializationVisibilityAttribute Class (MSDN)

ASP.Net User Controls Overview (MSDN)

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