* MultiSelect Treeview

[PWagner1]

Multi-select TreeView (KryptonMultiSelectTreeView)

Closes #3837

Summary

Adds KryptonMultiSelectTreeView to Krypton.Toolkit.Utilities, a KryptonTreeView derivative with ListView-style extended selection for hierarchical data. The control exposes a SelectedNodes collection and supports Ctrl+click toggle, Shift+click range selection, rubber-band drag selection, and optional check-box selection that stays in sync with SelectedNodes.

A small, backward-compatible extension to core KryptonTreeView adds protected virtual IsNodeMultiSelected(TreeNode) so additional selected nodes paint with the existing StateMultiSelect palette styling.

Motivation

WinForms TreeView is single-select at the OS level. Issue #3837 requested a Krypton-styled control with:

• Ctrl+click discrete selection
• Shift+click range selection (visible flat order)
• Click-drag rubber-band selection
• Check-box selection
• A SelectedNodes return type / collection API

KryptonTreeView already had partial checkbox-toggle multi-select via MultiSelect; this PR delivers the full feature set as a dedicated Utilities control scoped for V110.

Changes

New: KryptonMultiSelectTreeView (Krypton.Toolkit.Utilities)

Area	Details
Control	Components/KryptonMultiSelectTreeView/Controls Toolkit/KryptonMultiSelectTreeView.cs

Public API

• SelectedNodes — ReadOnlyCollection<TreeNode>
• SelectedNodesChanged — default event
• EnableRubberBandSelection (default true)
• SyncCheckBoxesToSelection (default true)
• SetSelectedNodes(IEnumerable<TreeNode>)
• ClearSelectedNodes()
• SelectAllVisibleNodes()

Base KryptonTreeView.MultiSelect is hidden; this control manages its own selection model.

Core: KryptonTreeView

• Added protected virtual bool IsNodeMultiSelected(TreeNode node) (default false)
• Owner-draw path treats multi-selected nodes as selected for row highlight, images, and StateMultiSelect / StateCheckedMultiSelect palette overrides

No breaking changes to existing KryptonTreeView consumers.

TestForm

• MultiSelectTreeViewExample — demo form with sample hierarchy, live selection label, Clear / Select All buttons
• Start screen entry: Multi-Select TreeView

Changelog

• V110 nightly entry under #3837

Behaviour notes

Interaction	Behaviour
Plain click	Selects a single node; updates SelectedNodes and check boxes (when enabled)

Rubber-band overlay is painted on the outer KryptonMultiSelectTreeView (not inner TreeView.Paint) because Krypton uses a custom WmPaint path on the hosted tree.

Implementation details

• 64-bit TVM_GETITEMRECT: HTREEITEM is passed via Marshal.WriteIntPtr into the first pointer-sized field of RECT (matches WinForms TreeNode.Bounds), with fallback to TopNode / NextVisibleNode layout
• Rubber-band vs modifiers: Mouse-down defers plain clicks when rubber-banding is enabled so drag does not fight single-select; Ctrl/Shift clicks are handled immediately in BeforeSelect
• Check-box sync: All nodes in the tree are updated inside BeginUpdate/EndUpdate; sync runs after focus changes and on selection no-op paths so Shift+click range keeps check states aligned

Test plan

Manual validation via TestForm → Multi-Select TreeView:

• Plain click selects one node; label shows SelectedNodes; check box checks
• Ctrl+click toggles multiple non-contiguous nodes on/off (highlight + check boxes)
• Click node A, Shift+click node C — range A–C selected and checked; nodes outside range unchecked
• Drag rubber band across several rows — band visible, nodes on release selected (Ctrl+drag extends)
• Select All / Clear Selection buttons
• Theme switch — multi-select highlights use Krypton palette (StateMultiSelect)
• Build: Krypton.Toolkit.Utilities and TestForm on net48 and net11.0-windows

Packaging

Ships in the Krypton.Toolkit.Utilities assembly (same NuGet surface as other Utilities controls, e.g. KryptonCircularProgressBar, KryptonTreeComboBox).