doc(TreeView): update sample code prevent page not avaliable

[ArgoZhang]

Link issues

fixes #7827

Summary By Copilot

Regression?

• Yes
• No

Risk

• High
• Medium
• Low

Verification

• Manual (required)
• Automated

Packaging changes reviewed?

• Yes
• No
• N/A

☑️ Self Check before Merge

⚠️ Please check all items below before review. ⚠️

• Doc is updated/provided or not needed
• Demo is updated/provided or not needed
• Merge the latest code from the main branch

Summary by Sourcery

Ensure TreeView draggable sample uses an instance-level data source instead of shared static state to avoid cross-page interference.

Bug Fixes:

• Prevent TreeView draggable demo from sharing drag source data across pages by using an instance-local item collection as the data source.

Enhancements:

• Simplify TreeView sample data initialization and make IconItems instance-scoped for consistency with other demo item collections.

[sourcery-ai]

Reviewer's Guide

Refactors the TreeView drag-and-drop demo to use an instance-scoped source list and non-static icon items, ensuring consistent state updates when dragging nodes while simplifying the draggable item factory method.

Sequence diagram for updated TreeView drag-and-drop handling

sequenceDiagram
    actor User
    participant TreeViewComponent
    participant TreeViews
    participant DraggableSourceItems

    User->>TreeViewComponent: drag node and drop on target
    TreeViewComponent->>TreeViews: OnDragItemEndAsync(context)
    activate TreeViews

    TreeViews->>DraggableSourceItems: find source by context.Source.Value.Id
    DraggableSourceItems-->>TreeViews: source TreeFoo

    TreeViews->>DraggableSourceItems: find target by context.Target.Value.Id
    DraggableSourceItems-->>TreeViews: target TreeFoo

    TreeViews->>TreeViews: update source.ParentId and ordering
    TreeViews->>TreeViews: DraggableItems = TreeFoo.CascadingTree(DraggableSourceItems, callback)

    TreeViews-->>TreeViewComponent: updated DraggableItems
    deactivate TreeViews

    TreeViewComponent-->>User: render updated TreeView

Loading

File-Level Changes

Change	Details	Files
Refactor draggable TreeView sample to use an instance-level source list instead of recreating or caching static data.	Introduce DraggableSourceItems as an instance property initialized from GetDraggableItems() Update OnInitialized to build DraggableItems from DraggableSourceItems instead of a freshly created list Update OnDragItemEndAsync to find and manipulate source/target nodes within DraggableSourceItems Rebuild DraggableItems from DraggableSourceItems after drag operations while preserving expansion logic	src/BootstrapBlazor.Server/Components/Samples/TreeViews.razor.cs
Align TreeView sample properties and helpers with instance-based patterns and simplify the draggable item factory.	Change IconItems from static settable property to an instance get-only property initialized via TreeFoo.GetTreeItems() Replace the previously cached static _dragItems pattern with a simple static GetDraggableItems() method that returns a new list literal of TreeFoo items	src/BootstrapBlazor.Server/Components/Samples/TreeViews.razor.cs

Assessment against linked issues

Issue	Objective	Addressed	Explanation
#7827	Update the TreeView sample component code so that the draggable TreeView no longer causes a 'page not available' or runtime error (by fixing how the draggable data source is managed).	✅
#7827	Ensure the TreeView sample/demo code is valid and reflects the correct usage pattern for draggable items and icon items in the documentation/site.	✅

Possibly linked issues

• doc(TreeView): update sample code prevent page not avaliable #7827: PR updates TreeView draggable sample code, matching the issue’s request to prevent page not available.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (b133314) to head (7b6082d).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #7828   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          764       764           
  Lines        34142     34142           
  Branches      4701      4701           
=========================================
  Hits         34142     34142           

Flag	Coverage Δ
BB	100.00% <ø> (?)

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[Copilot]

Pull request overview

Updates the TreeView sample component to avoid shared/static state in the draggable TreeView demo, which can lead to invalid demo data and navigation failures (“page not available”) across sessions.

Changes:

• Introduces a per-component DraggableSourceItems data source and reuses it during drag operations.
• Removes the previously cached static draggable items list and makes IconItems instance-scoped.

Comments suppressed due to low confidence (2)

src/BootstrapBlazor.Server/Components/Samples/TreeViews.razor.cs:96

• DraggableItems[0] is accessed unconditionally. If CascadingTree(DraggableSourceItems) ever returns an empty list (e.g., source data ends up with no root nodes), this will throw and break the sample page. Guard with if (DraggableItems.Count > 0) before indexing, and apply the same pattern to the subsequent [1]/[2] expansions.

        DraggableItems = TreeFoo.CascadingTree(DraggableSourceItems);
        DraggableItems[0].IsExpand = true;
        if (DraggableItems.Count > 1)
        {
            DraggableItems[1].IsExpand = true;
        }

src/BootstrapBlazor.Server/Components/Samples/TreeViews.razor.cs:140

• After rebuilding DraggableItems, the code indexes DraggableItems[0] without checking Count. A drag operation can potentially result in a hierarchy with no root nodes, making CascadingTree return an empty list and causing an IndexOutOfRangeException. Add a Count > 0 guard (and keep the existing Count > 1/2 checks) before setting IsExpand.

        DraggableItems = TreeFoo.CascadingTree(DraggableSourceItems, cb);
        DraggableItems[0].IsExpand = true;
        if (DraggableItems.Count > 1)
        {
            DraggableItems[1].IsExpand = true;
        }

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