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SupportsPreviewControlAttribute Class

Indicates whether a control designer requires a preview instance of the control at design time. This class cannot be inherited.

Namespace:  System.Web.UI.Design
Assembly:  System.Design (in System.Design.dll)

public sealed class SupportsPreviewControlAttribute : Attribute

Apply the SupportsPreviewControlAttribute attribute to a control designer class to indicate the type of preview control that is supported by the control designer. Use this attribute to change a preview control for design-time rendering without affecting the actual persisted instance of the associated control.

Typically, you specify the SupportsPreviewControlAttribute when declaring a custom designer class that is derived from the ControlDesigner class. The value of the SupportsPreviewControl property for the SupportsPreviewControlAttribute attribute determines the behavior for the UsePreviewControl and ViewControl members in the base ControlDesigner class.

Set the SupportsPreviewControl property to true to indicate that the designer uses a temporary copy of the associated control to generate the design-time HTML. Changes to the temporary control are not persisted.

Set the SupportsPreviewControl property to false to indicate that the designer returns the control instance, specifically the Component property, from the ViewControl method. Changes to the control object are persisted.

For example, the CalendarDesigner class is marked with the SupportsPreviewControlAttribute set to true. The designer uses the preview control with the automatic style formatting task, which allows the user to preview various autoformat styles that can be applied to the calendar. As the user selects different autoformat styles in the user interface, the selected style scheme is applied to the preview control. Applying a new style to the preview control does not change the scheme that is applied to the instance of the Calendar control in the designer.

If the SupportsPreviewControlAttribute is not specified in the control designer declaration, the ControlDesigner behavior is equivalent to specifying the SupportsPreviewControl as false.


Designer classes derived from the ControlDesigner class can override the UsePreviewControl and ViewControl members, and ignore the SupportsPreviewControlAttribute attribute. To determine the expected behavior for ViewControl and UsePreviewControl, see the reference documentation for the derived control designer class.

For general information about using attributes, see Attributes Overview and Extending Metadata Using Attributes. For more information about design-time attributes, see Attributes and Design-Time Support.

The following code example demonstrates how to mark a control designer with the SupportsPreviewControlAttribute attribute. The code example derives an ASP.NET server control from the Label class and associates the ASP.NET server control with a custom control designer implementation. The control designer class declaration is marked with the SupportsPreviewControl attribute set to true. The control designer overrides the GetDesignTimeHtml method and encloses the design-time HTML for the control in italic tags.

using System;
using System.ComponentModel;
using System.ComponentModel.Design;
using System.Web.UI;
using System.Web.UI.Design;
using System.Web.UI.Design.WebControls;
using System.Web.UI.WebControls;
using System.Reflection;

namespace ControlDesignerSamples.CS
    // Define a simple designer associated with a  
    // simple text web control. 
    // Mark the designer with the SupportsPreviewControlAttribute set 
    // to true.  This means the base.UsePreviewControl returns true, 
    // and base.ViewControl returns a temporary preview copy of the control.
    public class SimpleTextControlDesigner : TextControlDesigner
        // Override the base GetDesignTimeHtml method to display  
        // the design time text in italics. 
        public override string GetDesignTimeHtml()
            string html = String.Empty;

                // Initialize the return string to the default 
                // design time html of the base TextControlDesigner.
                html = base.GetDesignTimeHtml();

                // Get the ViewControl for the associated control.
                Label ctrl = (Label)ViewControl;

                ctrl.Style.Add(HtmlTextWriterStyle.FontStyle, "Italic");
                html = base.GetDesignTimeHtml();

            catch (System.Exception e)
               if (String.IsNullOrEmpty(html))
                   html = GetErrorDesignTimeHtml(e);

            return html;


    // Derive a simple Web control from Label to render a text string. 
    // Associate this control with the SimpleTextControlDesigner.
    ToolboxData("<{0}:MyLabelControl Runat=\"Server\"><{0}:MyLabelControl>")]
    public class MyLabelControl : Label
        // Use the Label control implementation, but associate 
        // the derived class with the custom control designer.


Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0