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HtmlTextWriter.FilterAttributes Method

  • Reference

Definition

Namespace:
System.Web.UI
Assembly:
System.Web.dll

Removes all the markup and style attributes on all properties of the page or Web server control.

protected:
 virtual void FilterAttributes();
protected virtual void FilterAttributes ();
abstract member FilterAttributes : unit -> unit
override this.FilterAttributes : unit -> unit
Protected Overridable Sub FilterAttributes ()

Examples

The following code example shows how to use a custom class, derived from the HtmlTextWriter class, that overrides the FilterAttributes method. When called, the FilterAttributes override checks whether the text writer renders any <label> or <a> elements:

  • If a <label> element is being rendered, the FilterAttributes method checks whether a style attribute is rendered on the element and, if not, creates a style attribute and sets it to color: blue.

  • If an <a> element is being rendered, the FilterAttributes method determines whether an href attribute is included and, if not, adds an href to the URL http://www.cohowinery.com.

// Override the FilterAttributes method to check whether 
// <label> and <anchor> elements contain specific attributes. 
virtual void FilterAttributes() override
{
   // If the <label> element is rendered and a style
   // attribute is not defined, add a style attribute 
   // and set its value to blue.
   if ( TagKey == HtmlTextWriterTag::Label )
   {
      if (  !IsAttributeDefined( HtmlTextWriterAttribute::Style ) )
      {
         AddAttribute( "style", EncodeAttributeValue( "color:blue", true ) );
         Write( NewLine );
         Indent = 3;
         OutputTabs();
      }
   }

   // If an <anchor> element is rendered and an href
   // attribute has not been defined, call the AddAttribute
   // method to add an href attribute
   // and set it to http://www.cohowinery.com.
   // Use the EncodeUrl method to convert any spaces to %20.
   if ( TagKey == HtmlTextWriterTag::A )
   {
      if (  !IsAttributeDefined( HtmlTextWriterAttribute::Href ) )
      {
         AddAttribute( "href", EncodeUrl( "http://www.cohowinery.com" ) );
      }
   }

   // Call the FilterAttributes method of the base class.
   __super::FilterAttributes();
}

// Override the FilterAttributes method to check whether 
// <label> and <anchor> elements contain specific attributes.      
protected override void FilterAttributes()
{
    // If the <label> element is rendered and a style
    // attribute is not defined, add a style attribute 
    // and set its value to blue.
    if (TagKey == HtmlTextWriterTag.Label)
    {
        if (!IsAttributeDefined(HtmlTextWriterAttribute.Style))
        {
            AddAttribute("style", EncodeAttributeValue("color:blue", true));
            Write(NewLine);
            Indent = 3;
            OutputTabs();
        }
    }

    // If an <anchor> element is rendered and an href
    // attribute has not been defined, call the AddAttribute
    // method to add an href attribute
    // and set it to http://www.cohowinery.com.
    // Use the EncodeUrl method to convert any spaces to %20.
    if (TagKey == HtmlTextWriterTag.A)
    {
        if (!IsAttributeDefined(HtmlTextWriterAttribute.Href))
        {
            AddAttribute("href", EncodeUrl("http://www.cohowinery.com"));
        }
    }
    // Call the FilterAttributes method of the base class.
    base.FilterAttributes();
}

' Override the FilterAttributes method to check whether 
' <label> and <anchor> elements contain specific attributes.   
Protected Overrides Sub FilterAttributes()

    ' If the <label> element is rendered and a style
    ' attribute is not defined, add a style attribute 
    ' and set its value to blue.
    If TagKey = HtmlTextWriterTag.Label Then
        If Not IsAttributeDefined(HtmlTextWriterAttribute.Style) Then
            AddAttribute("style", EncodeAttributeValue("color:blue", True))
            Write(NewLine)
            Indent = 3
            OutputTabs()
        End If
    End If
    ' If an <anchor> element is rendered and an href
    ' attribute has not been defined, call the AddAttribute
    ' method to add an href attribute
    ' and set it to http://www.cohowinery.com.
    ' Use the EncodeUrl method to convert any spaces to %20.
    If TagKey = HtmlTextWriterTag.A Then
        If Not IsAttributeDefined(HtmlTextWriterAttribute.Href) Then
            AddAttribute("href", EncodeUrl("http://www.cohowinery.com"))
        End If
    End If

    ' Call the FilterAttributes method of the base class.
    MyBase.FilterAttributes()
End Sub

Remarks

Before attributes are rendered on a markup element, the FilterAttributes method is called. In turn, the FilterAttributes method calls the OnAttributeRender and OnStyleAttributeRender methods for each attribute and style to render.

Applies to

See also