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HtmlTextWriter.IsAttributeDefined Method (HtmlTextWriterAttribute)

Determines whether the specified markup attribute and its value are rendered during the next call to the RenderBeginTag method.

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

protected bool IsAttributeDefined(
	HtmlTextWriterAttribute key


Type: System.Web.UI.HtmlTextWriterAttribute
The HtmlTextWriterAttribute associated with the markup attribute.

Return Value

Type: System.Boolean
true if the attribute is rendered during the next call to the RenderBeginTag method; otherwise, false.

To obtain the value to be assigned to the HtmlTextWriterAttribute object, use the IsAttributeDefined(HtmlTextWriterAttribute, String) overload instead of this one.

The following code example shows how to use an override of the RenderBeginTag method in a class that inherits from the HtmlTextWriter class. The RenderBeginTag override checks whether a <font> markup element will be rendered. If so, the override calls the IsAttributeDefined method to check whether the <font> element contains a Size attribute. If not, the AddAttribute method calls the GetAttributeKey method, which defines the Size attribute and sets its value to 30pt.

// If the tagKey parameter is set to a <font> element
// but a size attribute is not defined on the element,
// the AddStyleAttribute method adds a size attribute
// and sets it to 30 point. 
if (tagKey == HtmlTextWriterTag.Font)
    if (!IsAttributeDefined(HtmlTextWriterAttribute.Size))
        AddAttribute(GetAttributeKey("size"), "30pt");

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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