DesktopTreeViewLibrary API

Overview

DesktopTreeViewLibrary provides a pixel-scrolling TreeView for Xojo Desktop. It consists of:

• DesktopTreeViewCntrl (ContainerControl): owns scrollbar and layout
• XojoTreeView (Canvas-based control): owns rendering, hit-testing, row rebuilding, and scroll physics

This file documents the current cleaned API only.

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Public API (v1.0)

XojoTreeView

BeginUse(rootTree As Dictionary, levelSpec As Dictionary, host As Object)

Bind the tree view to its data and host. This is a one-time operation.

Update()

Call after mutating the bound tree structure to rebuild rows and refresh display.

SetScrollY(y As Integer)

Set vertical scroll position in pixels. Value is clamped internally.

MaxScrollY() As Integer

Returns the maximum legal scroll position in pixels for the current content.

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Callbacks

ScrollChanged

Emitted when the tree scroll position changes (mouse wheel, drag, expand/collapse).

• payload: current scroll position in pixels (string form)

The host is expected to:

• update scrollbar MaximumValue using MaxScrollY
• clamp scrollbar Value
• guard against feedback loops

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Visibility Notes

• Fire(...) is Protected
  • prevents external event spoofing
  • allows subclasses to emit legitimate notifications

All rendering, layout, and rebuild helpers are Private.

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Scrolling Model

• Pixel-based scrolling
• Scrollbar.Value == mScrollY
• Scrollbar.MaximumValue == MaxScrollY
• Scrollbar.PageStep == viewport height

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Expand / Collapse Contract

When a disclosure triangle is clicked:

1. Toggle _Expanded
2. Rebuild visible rows immediately
3. Clamp scroll
4. Refresh view
5. Emit ScrollChanged

This guarantees scrollbar and mouse wheel never desync.

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Tree Node Dictionary Keys

Reserved keys:

• _Key : String (unique id)
• _Value : display value
• _Expanded : Boolean
• _Children : Dictionary (child nodes)

Additional domain-specific keys are allowed.

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Minimal Usage

Bind once: XTree.BeginUse(rootDict, levelSpec, Self)

After tree mutation: XTree.Update

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API frozen for v1.0.