VirtualizingPanel

Remarks

The items are the caller's and the rows are a pool. This control knows how many items there are and how tall a row is; it does not know what an item is. A hundred thousand of them is a hundred thousand of the caller's own objects and about thirty elements, rebound as the view scrolls — which is doc 09's claim about a data grid, made once here instead of again in each control that wants it.

⚠ Rows are positioned absolutely, at a fixed height. Virtualisation needs to know where row 40 000 is without having measured the 39 999 above it, and a fixed height makes that arithmetic instead of a walk. Variable heights need a running-sum index maintained as things change size; that is a different control and is owed rather than approximated.

⚠ Nothing has to call Realise. It runs on LayoutFinished, which is the only place that knows how tall the viewport ended up — so a panel resized without being scrolled realises against the size it actually has. That is the gap every explicit Refresh() in this library existed for, and the reason the callback was built.

Fields and properties (11)

• public const int Overscan

  How many rows are realised above and below the viewport.

• protected override string TagName

  The element name this type answers to when a caller does not choose one.

• protected override bool AcceptsFocus

  Whether the focus can rest on this kind of control at all.

• public ScrollView Scroller

  The scroller the rows live in.

• public IReadOnlyList<UiElement> Rows

  The rows that exist as elements, in pool order rather than in item order.

• public int FirstItem

  Which item the first row of the pool is showing.

• public float RowHeight

  How tall a row is, from --row-height.

• public int Count
• public Func<VirtualizingPanel, UiElement>? CreateRow

  Makes a row element. Called only when the pool has to grow.

• public Action<UiElement, int>? BindRow

  Puts an item's data on a row. Called whenever a row starts showing a different item.

• public static readonly UiPropertyKey CountProperty

  Identity for Count.

Methods (6)

• protected override void OnCreated()

  Builds whatever this element is made of, once, as it joins a document.

• protected override void OnRemoved()

  Called once, as the element leaves the document.

• public UiElement? RowOf(int item)

  The element showing an item, or null if it is not realised.

• public void ScrollIntoView(int item)

  Scrolls until an item is inside the viewport.

• public void Realise()

  Makes sure there is a row for every visible line of the viewport, and binds them.

• public void ClearCount()

  Unsets Count, so it takes its default or its ancestor's value again.

Used by (7)

• TreeViewVixen.Ui.Controls.Advanced
• VirtualizingGridVixen.Ui.Controls
• VirtualizingPanelTestsVixen.Ui.Controls.Tests
• ConsolePanelTestsVixen.Editor.App.Tests
• ConsoleViewVixen.Editor.Ui
• ConsoleViewTestsVixen.Editor.Ui.Tests
• MessageLogViewVixen.Editor.Ui