SupportsPreviewControlAttribute Class


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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


Initializes a new instance of the SupportsPreviewControlAttribute class and sets the initial value of the SupportsPreviewControl property.


Gets a value indicating whether the control designer requires a temporary preview control at design time.


When implemented in a derived class, gets a unique identifier for this Attribute.(Inherited from Attribute.)


Determines whether the specified object represents the same preview attribute setting as the current instance of the SupportsPreviewControlAttribute class.(Overrides Attribute.Equals(Object).)


Returns the hash code for this instance of the SupportsPreviewControlAttribute class.(Overrides Attribute.GetHashCode().)


Gets the Type of the current instance.(Inherited from Object.)


Indicates whether the current instance of the SupportsPreviewControlAttribute class is set to the default preview attribute value.(Overrides Attribute.IsDefaultAttribute().)


When overridden in a derived class, returns a value that indicates whether this instance equals a specified object.(Inherited from Attribute.)


Returns a string that represents the current object.(Inherited from Object.)


Gets an instance of the SupportsPreviewControlAttribute class that is set to the default preview value. This field is read-only.

System_CAPS_pubinterfaceSystem_CAPS_privmethod_Attribute.GetIDsOfNames(Guid, IntPtr, UInt32, UInt32, IntPtr)

Maps a set of names to a corresponding set of dispatch identifiers.(Inherited from Attribute.)

System_CAPS_pubinterfaceSystem_CAPS_privmethod_Attribute.GetTypeInfo(UInt32, UInt32, IntPtr)

Retrieves the type information for an object, which can be used to get the type information for an interface.(Inherited from Attribute.)


Retrieves the number of type information interfaces that an object provides (either 0 or 1).(Inherited from Attribute.)

System_CAPS_pubinterfaceSystem_CAPS_privmethod_Attribute.Invoke(UInt32, Guid, UInt32, Int16, IntPtr, IntPtr, IntPtr, IntPtr)

Provides access to properties and methods exposed by an object.(Inherited from 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 stylesthat 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.

.NET Framework
Available since 2.0

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

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