Virtual Elements

From PowerUI
Revision as of 23:27, 3 April 2017 by 151.229.136.200 (talk) (Accessing virtual elements)
Jump to: navigation, search

Virtual elements are created whenever CSS requires an element to be rendered but must not pollute the DOM. Importantly, virtual elements are ordered. For example, the virtual element created by ::after shows up after the 'real' element has been drawn. PowerUI handles this by storing all virtual elements in a SortedDictionary, indexed by a priority value. It's unique and constant for any given type of virtual element.

Accessing virtual elements

There's a web API for doing this which is supported - specifically the element.getComputedStyle("after") method:

// Get the computed style for the '::after' selector:
var after = element.getComputedStyle("after");

// (Then use e.g. after.Element)

For more advanced uses, you can directly access the set of virtual elements here:

// Get the virtuals set for 'element' (A HtmlElement):
Css.VirtualElements virtuals=element.Style.Computed.Virtuals;

Note that it's null if there aren't any.

The priority value

You'll notice that the virtuals set uses those arbitrary priority values. In order to obtain a particular virtual element, you'll need to know what its priority is - fortunately, they're constant for any given type of element:

Virtual Element Priority (C# const) See Also
Horizontal scrollbar ComputedStyle.HorizontalScrollPriority Styling scrollbars
Vertical scrollbar ComputedStyle.VerticalScrollPriority Styling scrollbars
Textarea/ input field caret HtmlCaretElement.Priority Styling the caret
Select menu dropdown HtmlDropdownElement.Priority It's a virtual <dropdown> element (style it by selecting that).
Select menu down arrow HtmlSelectButtonElement.Priority It's a virtual <selectbutton> element (style it by selecting that).
 ::before BeforeSelector.Priority
 ::after AfterSelector.Priority
 ::marker MarkerSelector.Priority

What can I do with them?

They're completely ordinary elements which act exactly the same as a child of the element they're on. Essentially, you can do whatever you can normally do to elements to them too (The element itself is accessed from ComputedStyle.Element).