Imported from syncfusion/blazor-ui-components-skills (skills/syncfusion-blazor-diagram/SKILL.md). Install upstream with npx skills add syncfusion/blazor-ui-components-skills --skill syncfusion-blazor-diagram. Copyright stays with the author.

Implementing Syncfusion Blazor Diagram

A comprehensive skill for building interactive diagrams with the Syncfusion Blazor Diagram component — flowcharts, organizational charts, mind maps, BPMN process diagrams, UML sequence diagrams, network diagrams, and more.

When to Use This Skill

Use this skill when you need to:

• Create flowcharts, org charts, mind maps, or network diagrams in Blazor
• Work with SfDiagramComponent, nodes, connectors, or shapes
• Configure automatic layouts (hierarchical, radial, mind map, org chart, flowchart)
• Implement BPMN process diagrams with BPMN shapes
• Build swimlane diagrams for process modeling
• Add symbol palettes for drag-and-drop diagram building
• Bind diagram data from a collection or remote source
• Implement diagram interactions (selection, drag, resize, zoom, pan)
• Export diagrams to PNG/JPEG/SVG or print them
• Serialize and restore diagram state (save/load)
• Enable collaborative real-time editing
• Add UML sequence diagrams
• Handle diagram events, annotations, and ports

Important: API Verification Required

API Verification Required: Always verify API class names, properties, and signatures by reading reference files (references/*.md) BEFORE generating code examples. Do not assume or infer class names. ⚠️ Before writing ANY code, review the Common Mistakes section directly below to avoid known invalid APIs and properties.

Quick Start

@using Syncfusion.Blazor.Diagram

<SfDiagramComponent Width="100%" Height="600px" Nodes="@nodes" Connectors="@connectors" />

@code {
    DiagramObjectCollection<Node> nodes = new DiagramObjectCollection<Node>
    {
        new Node
        {
            ID = "node1", OffsetX = 150, OffsetY = 150,
            Width = 100, Height = 50,
            Style = new ShapeStyle { Fill = "#6BA5D7", StrokeColor = "white" },
            Annotations = new DiagramObjectCollection<ShapeAnnotation>
            {
                new ShapeAnnotation { Content = "Start" }
            }
        }
    };
    DiagramObjectCollection<Connector> connectors = new DiagramObjectCollection<Connector>
    {
        new Connector { ID = "conn1", SourceID = "node1", TargetID = "node2" }
    };
}

Common Patterns

Documentation and Navigation Guide

Getting Started

📄 Read: references/getting-started.md

• NuGet package installation (Syncfusion.Blazor.Diagram)
• Service registration and namespace imports
• Setup for Blazor Server, WebAssembly, MAUI
• CSS/theme configuration
• Minimal working diagram example

Nodes

📄 Read: references/nodes.md

• Creating and configuring nodes
• Node types: basic, flow shape, path, image, HTML, native
• Node positioning, sizing, z-order
• Node style (fill, stroke, opacity)
• Expand/collapse children
• Node events and interaction

Connectors

📄 Read: references/connectors.md

• Creating connectors between nodes or free-floating
• Segment types: straight, orthogonal, bezier
• Multiple segments per connector
• Arrows, line style, and decoration
• Connector interaction (bend, drag endpoints)
• Connector events

Shapes

📄 Read: references/shapes.md

• Built-in basic shapes (rectangle, ellipse, triangle, etc.)
• Flow shapes (process, decision, terminator, etc.)
• Path shapes (custom SVG paths)
• Image and HTML content shapes
• Native SVG shapes
• Choosing the right shape type

Annotations

📄 Read: references/annotations.md

• Adding text labels to nodes and connectors
• Annotation positioning and alignment
• Font, color, and style customization
• Inline editing of annotations
• Multiple annotations per element
• Annotation interaction events
• Interaction constraints: AnnotationConstraints flags, DragLimit (PathAnnotation)
• Hyperlinks with Hyperlink (Url, Content, OpenMode)
• Events: SelectionChanging/Changed, PositionChanging/Changed, SizeChanging/Changed, RotationChanging/Changed, TextChanging/Changed

Ports

📄 Read: references/ports.md

• Connection ports (fixed connection points on nodes)
• Dynamic ports (created at runtime)
• Port positioning (relative and absolute)
• Port appearance and visibility
• Restricting connections to specific ports

Layout

📄 Read: references/layout.md

• Automatic layout overview and when to use each type
• Hierarchical tree layout (top-down, left-right)
• Organizational chart layout
• Mind map layout
• Radial tree layout
• Flowchart layout
• Force-directed tree layout
• Complex hierarchical layout
• Layout spacing, margin, and orientation settings
• Layout events and callbacks
• await DoLayoutAsync() — refresh layout at runtime after adding/removing nodes

Swimlane

📄 Read: references/swimlane.md

• Creating swimlane diagrams
• Adding lanes and configuring lane properties
• Phase configuration (vertical/horizontal phases)
• Swimlane symbol palette integration
• Swimlane interactions

<SfDiagramComponent Height="600px" Swimlanes="@swimlanes" />

@code {
    DiagramObjectCollection<Swimlane> swimlanes = new();

    protected override void OnInitialized()
    {
        swimlanes.Add(new Swimlane
        {
            ID = "swimlane1",
            OffsetX = 400, OffsetY = 300,
            Width = 600, Height = 200,
            Lanes = new DiagramObjectCollection<Lane>()
            {
                new Lane(){
                Height = 100,
                Header = new SwimlaneHeader(){
                    Width = 30,
                    Annotation = new ShapeAnnotation(){ Content = "Consumer" }
                },
                Children = new DiagramObjectCollection<Node>()
                {
                    new Node(){Height = 50, Width = 50, LaneOffsetX = 250, LaneOffsetY = 30},
                }
                },
            }
        });
    }
}

BPMN

📄 Read: references/bpmn.md

• BPMN shape types (events, activities, gateways, data)
• BPMN event types (start, end, intermediate, boundary)
• BPMN activity types (task, subprocess, call activity)
• BPMN gateway types (exclusive, parallel, inclusive, etc.)
• BPMN connectors (sequence flow, message flow, association)
• Data objects and data stores
• Expanded sub-process
• BPMN text annotation

// Exclusive gateway (XOR)
nodes.Add(new Node
{
    ID = "gateway1", OffsetX = 300, OffsetY = 200, Width = 50, Height = 50,
    Shape = new BpmnGateway
    {
        GatewayType = BpmnGatewayType.Exclusive
    }
});

Symbol Palette

📄 Read: references/symbol-palette.md

• Setting up SfSymbolPaletteComponent
• Defining palette groups and symbols
• Custom symbols and stencils
• Drag-and-drop from palette to diagram
• Palette search and customization

Data Binding

📄 Read: references/data-binding.md

• Binding diagram from a flat list or IEnumerable
• Hierarchical data binding (parent-child relationships)
• Remote data source integration
• Runtime CRUD: await ReadDataAsync(query?), await InsertDataAsync(data), await UpdateDataAsync(keyField, data), await DeleteDataAsync(keyField, value)
• await RefreshDataSourceAsync() — reload all data and rebuild layout
• Mapping data fields to node/connector properties

Interaction & Commands

📄 Read: references/interaction.md

• Selection: Select(collection, multipleSelection?), SelectAll(), UnSelect(obj), ClearSelection()
• Drag, resize, and rotate elements (user interaction + programmatic)
• Programmatic transforms: Drag(obj, tx, ty), Rotate(obj, angle, pivot?), Scale(obj, sx, sy, pivot)
• Zoom and pan: mouse wheel, toolbar, Zoom(factor, focusPoint), ResetZoom(), Pan(hOffset, vOffset, focusPoint?)
• BringIntoView(DiagramRect) — scroll viewport to show a region
• BringIntoCenter(DiagramRect) — scroll viewport to center a region
• FitToPage(FitOptions?) — fit content to viewport (sync; FitMode.Width/Height/Both, DiagramRegion.Content/PageSettings)
• Nudge(Direction, int?) — move selected elements by pixels; default 1px; Direction.Top/Bottom/Left/Right
• Z-Order: BringToFront(), BringForward(), SendBackward(), SendToBack() — must Select() first
• Clipboard: Copy(), Cut(), Paste(collection?), Delete(collection?)
• Group/Ungroup: Group(), Ungroup(), AddChildAsync(group, child), RemoveChild(group, child)
• Inline text editing: StartTextEdit(obj, annotationId?)
• Keyboard shortcuts (built-in table) and CommandManager (custom/override shortcuts via child component)
• CommandManager uses KeyboardCommand + KeyGesture (DiagramKeys + ModifierKeys) + CommandKeyArgs
• Snapping to grid or objects
• Alignment, spacing, and sizing commands (SetAlign, SetDistribute, SetSameSize — all sync)
• User handles (custom action buttons on selection)
• Undo/redo: Undo(), Redo() (sync); StartGroupAction() / EndGroupAction() for batched undo steps
• History: AddHistoryEntry(entry), ClearHistory()
• Utility: GetObject(id), GetPageBounds(x?, y?), Clear() (removes all elements)
• Batch updates: BeginUpdate() + await EndUpdateAsync() — group multiple changes into one render pass
• Add multiple elements: await AddDiagramElementsAsync(DiagramObjectCollection<NodeBase>)

Events

📄 Read: references/events.md

• Diagram-level events (Created, Click, Drop)
• Node events (NodeCreating, PositionChanged, SizeChanged)
• Connector events (ConnectionChanged, SegmentChanged)
• Selection events (SelectionChanged)
• History change events (HistoryChanged for undo/redo)
• Event argument types and usage patterns

Serialization

📄 Read: references/serialization.md

• Saving diagram state as JSON string
• Loading a diagram from saved JSON
• Custom serialization properties
• Partial diagram save and restore patterns

Export & Print

📄 Read: references/export-print.md

• Exporting to PNG, JPEG, SVG formats
• Export region options (diagram, page, content)
• Scale and margin settings
• Print configuration
• Custom page size and orientation
• Fit diagram to single page on print

Styling

📄 Read: references/styling.md

• CSS class customization (CssClass property)
• Built-in themes (Material, Bootstrap, Fluent, Tailwind)
• Node and connector style properties
• Selection and hover styles
• Theme Studio customization
• CSS variable overrides

UML Sequence Diagrams

📄 Read: references/uml-sequence.md

• UML sequence diagram setup
• Lifelines and activation boxes
• Message types (synchronous, asynchronous, return, create, destroy)
• UML interaction shapes and connectors
• await UpdateFromModelAsync() — refresh diagram after programmatic model changes

UML Class Diagram

📄 Read: references/uml-class-diagram.md

• Creating Class, Interface, and Enumeration nodes with attributes, methods, and members
• Visibility scopes, method parameters, separator rows
• Styling header, section headers (UmlSectionHeaderSettings), and row-level TextStyle
• Six relationship types: Association, Aggregation, Composition, Inheritance, Dependency, Realization
• Directional / bi-directional association flow; multiplicity labels
• Adding and removing members at runtime (Add, RemoveAt, Remove)
• CollectionChanging / CollectionChanged events; inline text editing (F2, StartTextEdit)
• Symbol Palette integration for drag-and-drop UML shapes

Collaborative Editing

📄 Read: references/collaborative-editing.md

• Setting up real-time collaborative diagram editing
• SignalR hub configuration
• Blazor Server and WASM app integration
• Handling real-time sync and conflict resolution
• Delta sync: GetDiagramUpdates(HistoryChangedEventArgs) + await SetDiagramUpdatesAsync(updates) — efficient change propagation

Overview Component

📄 Read: references/overview-component.md

• Adding SfDiagramOverviewComponent as a miniature thumbnail panel
• Linking the overview to the main diagram via SourceID / ID
• Controlling panel size with Width and Height
• Zoom and pan interactions (drag, resize, click, draw-region)
• Enabling or disabling interactions with DiagramOverviewConstraints
• Required @using Syncfusion.Blazor.Diagram.Overview namespace.

@using Syncfusion.Blazor.Diagram
@using Syncfusion.Blazor.Diagram.Overview
@using System.Collections.ObjectModel

<SfDiagramComponent ID="element"
                    Width="100%"
                    Height="500px">
</SfDiagramComponent>

<!-- Overview panel linked to the diagram above -->
<SfDiagramOverviewComponent Height="150px" SourceID="element" />

Advanced Features

📄 Read: references/advanced-features.md

• Context menu (built-in and custom items)
• Tooltips for nodes, connectors, ports, user handles
• Programmatic tooltips: await ShowTooltipAsync(obj) / await HideTooltipAsync(obj) — requires OpensOn = "Custom"
• Gridlines and rulers
• Scroll settings and page settings
• Container and group nodes
• Flip (horizontal/vertical)
• Constraints (restricting behavior per element)
• Localization (static text translation)
• Accessibility (WCAG 2.1, keyboard navigation)
• Migration from classic to native diagram

Common Mistakes

Annotation Editing

⚠️ AllowEditing does NOT exist on ShapeAnnotation or PathAnnotation.
Inline editing is on by default — no property is needed to enable it.
To disable editing, set Constraints = AnnotationConstraints.ReadOnly:

// ❌ Wrong — CS0117: AllowEditing does not exist
new ShapeAnnotation { Content = "Label", AllowEditing = false }

// ✅ Correct — use AnnotationConstraints.ReadOnly to disable editing
new ShapeAnnotation { Content = "Label", Constraints = AnnotationConstraints.ReadOnly }

EndUpdateAsync Method

⚠️ Always use EndUpdateAsync() (async) — EndUpdate() (sync, non-async) does NOT exist and will cause a compile error.
Use BeginUpdate()/EndUpdateAsync() when changing multiple properties at once — await is required:

// ❌ Wrong — EndUpdate() does not exist
diagram.BeginUpdate();
// ... changes ...
diagram.EndUpdate();

// ✅ Correct — EndUpdateAsync is async
diagram.BeginUpdate();
// ... changes ...
await diagram.EndUpdateAsync();

Click Event

⚠️ ClickEventArgs name collision: If your page also uses @using Syncfusion.Blazor.Navigations (or Buttons),
ClickEventArgs becomes ambiguous. Always qualify it:

// ✅ Use the fully qualified type in the handler signature
private void OnClick(Syncfusion.Blazor.Diagram.ClickEventArgs args) { }

⚠️ args.Count is NOT an int field — it is a method that returns an int.
Do NOT compare it directly with == inline without storing the result first:

// ❌ Wrong — CS0019: Operator '==' cannot be applied to operands of type 'method group' and 'int'
if (args.Count == 2)

// ✅ Correct — store result then compare
int clickCount = args.Count;
if (clickCount == 2) { /* double-click */ }

SizeChanged Event

⚠️ SizeChangedEventArgs.Element is typed as DiagramSelectionSettings, not Node.
Pattern-matching args.Element is Node n always fails with CS8121.
Cast to DiagramSelectionSettings and read .Nodes[0] to get the resized node:

// ❌ Wrong — CS8121: DiagramSelectionSettings cannot match Node
if (args.Element is Node n) { }

// ✅ Correct — Element is DiagramSelectionSettings
if (args.Element is DiagramSelectionSettings sel && sel.Nodes.Count > 0)
{
    var node = sel.Nodes[0];
    double w = args.NewValue.Width;
    double h = args.NewValue.Height;
}

⚠️ args.NewValue.Width and args.NewValue.Height are plain double, not double?.
Using ?? on them causes CS0019. Assign them directly:

// ❌ Wrong — CS0019
double w = args.NewValue.Width ?? 0;

// ✅ Correct
double w = args.NewValue.Width;

Selection Changed Event

⚠️ SelectionChangedEventArgs name collision: If your page also uses @using Syncfusion.Blazor.Buttons
(or other Syncfusion packages), SelectionChangedEventArgs becomes ambiguous. Always qualify it:

// ✅ Fully qualified
private void OnSelectionChanged(Syncfusion.Blazor.Diagram.SelectionChangedEventArgs args) { }

⚠️ args.NewValue is a DiagramSelectionSettings object — NOT a Node, NOT a collection:

• Pattern-matching args.NewValue is Node always fails with CS8121
• Iterating args.NewValue as a collection fails — it is a single settings object
• The only correct approach is to read _diagram.SelectionSettings.Nodes / .Connectors:

// ❌ Wrong — CS8121: DiagramSelectionSettings cannot match Node
if (args.NewValue is Node n) { }

// ❌ Wrong — DiagramSelectionSettings is not IEnumerable
foreach (var item in args.NewValue) { }

// ✅ Correct — use SelectionSettings on the diagram reference
foreach (var node in _diagram.SelectionSettings.Nodes)
    Console.WriteLine(node.ID);
foreach (var conn in _diagram.SelectionSettings.Connectors)
    Console.WriteLine(conn.ID);

Text Changed Event

⚠️ TextChangedEventArgs does NOT exist — using it causes CS0246.
The correct event args type is TextChangeEventArgs (no d):

// ❌ Wrong — CS0246: TextChangedEventArgs not found
private void OnTextChanged(TextChangedEventArgs args) { }

// ✅ Correct
private void OnTextChanged(TextChangeEventArgs args) { }

Drag Start Event

⚠️ DragStartEventArgs is ambiguous when Syncfusion.Blazor.Popups (or other packages that expose DragStartEventArgs) is also referenced.
Always qualify it as Syncfusion.Blazor.Diagram.DragStartEventArgs:

// ❌ Wrong — CS0104: ambiguous reference between Diagram and Popups
private void OnDragStart(DragStartEventArgs args) { }

// ✅ Correct — fully qualified
private void OnDragStart(Syncfusion.Blazor.Diagram.DragStartEventArgs args) { }

⚠️ DragEnterEventArgs does NOT exist in Syncfusion.Blazor.Diagram.
There is no DragEnter event on SfDiagramComponent that receives a DragEnterEventArgs.
The available drag events on SfDiagramComponent are: DragStart, Dragging, DragLeave, DragDrop — all for SymbolPalette drag-and-drop only.
For tracking when a node is being moved (internal drag), use PositionChanged:

// ❌ Wrong — DragEnterEventArgs does not exist
private void OnDragEnter(DragEnterEventArgs args) { }

// ❌ Wrong — OnPositionChange does not exist on SfDiagramComponent
<SfDiagramComponent OnPositionChange="OnPositionChange" />

// ✅ Correct — use PositionChanged
<SfDiagramComponent PositionChanged="OnPositionChanged" />

private void OnPositionChanged(PositionChangedEventArgs args)
{
    if (args.Element is Node n)
        Console.WriteLine($"Node {n.ID} moved to ({n.OffsetX}, {n.OffsetY})");
}

Snap Distance

⚠️ SnapObjectDistance does NOT exist on SnapSettings — using it causes InvalidOperationException: does not have a property matching the name 'SnapObjectDistance'.
The correct property name is SnapDistance:

@* ❌ Wrong — SnapObjectDistance does not exist *@
<SnapSettings SnapObjectDistance="5" />

@* ✅ Correct *@
<SnapSettings Constraints="SnapConstraints.SnapToObject" SnapDistance="5" />

Styling

⚠️ CssClass does NOT exist on SfDiagramComponent — using it causes
InvalidOperationException: Object of type 'SfDiagramComponent' does not have a property matching the name 'CssClass'.
Wrap the component in a <div> with a scoping class instead:

@* ❌ Wrong — CssClass does not exist on SfDiagramComponent *@
<SfDiagramComponent CssClass="my-diagram" />

@* ✅ Correct — use a wrapper div *@
<div class="my-diagram">
    <SfDiagramComponent ... />
</div>

Phase Offset Property

⚠️ Phase.Offset does NOT exist — using it causes a compile error.
Use Phase.Width to set the size of a phase in a swimlane:

// ❌ Wrong — Offset does not exist on Phase
new Phase { ID = "ph1", Offset = 220 }

// ✅ Correct — use Width
new Phase { ID = "ph1", Width = 220 }

Lane Constraints Property

⚠️ Lane.Constraints does NOT exist and LaneConstraints enum does NOT exist.
Individual lanes cannot have constraints set via a Constraints property.
To restrict swimlane-level interactions, use SwimlaneConstraints on the Swimlane object itself:

// ❌ Wrong — Lane.Constraints and LaneConstraints do not exist
lane.Constraints = LaneConstraints.Default & ~LaneConstraints.ResizeEntries;

// ✅ Correct — set constraints on the Swimlane object
swimlane.Constraints = SwimlaneConstraints.Default & ~SwimlaneConstraints.Interaction;

FitMode.Page Value

⚠️ FitMode.Page does NOT exist — using it causes CS0117.
The correct values for FitMode are FitMode.Width and FitMode.Height:

// ❌ Wrong — FitMode.Page does not exist
new FitOptions { Mode = FitMode.Page }

// ✅ Correct — use FitMode.Width or FitMode.Height
new FitOptions { Mode = FitMode.Width, Region = DiagramRegion.Content }

LoadDiagram Method

⚠️ SfDiagramComponent.LoadDiagram() does NOT exist — using it causes a compile error.
Use the async version LoadDiagramAsync() instead:

// ❌ Wrong — LoadDiagram() does not exist
diagram.LoadDiagram(savedJson);

// ✅ Correct — use LoadDiagramAsync
await diagram.LoadDiagramAsync(savedJson);

FitToPageAsync Method

⚠️ SfDiagramComponent.FitToPageAsync() does NOT exist — using it causes a compile error.
Use the non-async overload FitToPage() instead:

// ❌ Wrong — FitToPageAsync does not exist
await diagram.FitToPageAsync(new FitOptions { Mode = FitMode.Width });

// ✅ Correct — use FitToPage (synchronous)
diagram.FitToPage(new FitOptions { Mode = FitMode.Width, Region = DiagramRegion.Content });

BasicShapes Enum

⚠️ BasicShapes does NOT exist — use NodeBasicShapes instead:

// ❌ Wrong
new BasicShape { Shape = BasicShapes.Rectangle }

// ✅ Correct
new BasicShape { Shape = NodeBasicShapes.Rectangle }

DiagramThickness Constructor

⚠️ DiagramThickness does NOT have a 4-argument constructor — using it causes CS1729: does not contain a constructor that takes 4 arguments.
Use the object initializer syntax with named properties instead:

// ❌ Wrong — CS1729: no 4-argument constructor
new DiagramThickness(20, 50, 20, 20)

// ✅ Correct — use object initializer with named properties
new DiagramThickness { Left = 20, Top = 50, Right = 20, Bottom = 20 }

// ✅ Correct — set only the sides you need
new DiagramThickness { Top = 50 }

PathAnnotation DragLimit Type

⚠️ PathAnnotation.DragLimit type is DiagramThickness — NOT Margin.
Using new Margin { ... } causes a type mismatch compile error (CS0029).
Always use new DiagramThickness { ... } for DragLimit:

// ❌ Wrong — CS0029: Margin cannot be assigned to DiagramThickness
new PathAnnotation
{
    Constraints = AnnotationConstraints.Interaction,
    DragLimit   = new Margin { Left = 40, Right = 40, Top = 20, Bottom = 20 }
}

// ✅ Correct — DiagramThickness with object initializer
new PathAnnotation
{
    Constraints = AnnotationConstraints.Interaction,
    DragLimit   = new DiagramThickness { Left = 40, Right = 40, Top = 20, Bottom = 20 }
}

ScrollSettings EnableAutoScroll Property

⚠️ CanAutoScroll does NOT exist on ScrollSettings — using it causes InvalidOperationException: does not have a property matching the name 'CanAutoScroll'.
The correct property name is EnableAutoScroll:

@* ❌ Wrong — CanAutoScroll does not exist *@
<ScrollSettings CanAutoScroll="true" />

@* ✅ Correct *@
<ScrollSettings EnableAutoScroll="true" />

Zoom, Undo, and Redo Methods

⚠️ ZoomAsync(), UndoAsync(), and RedoAsync() do NOT exist — using them causes a compile error.
Use the non-async overloads Zoom(), Undo(), and Redo() instead:

// ❌ Wrong — ZoomAsync, UndoAsync, RedoAsync do not exist
await _diagram.ZoomAsync(1.2, new DiagramPoint { X = 300, Y = 300 });
await _diagram.UndoAsync();
await _diagram.RedoAsync();

// ✅ Correct — use non-async overloads
_diagram.Zoom(1.2, new DiagramPoint { X = 300, Y = 300 });
_diagram.Undo();
_diagram.Redo();

Overview Component Namespace

⚠️ SfDiagramOverviewComponent requires an additional @using — it lives in Syncfusion.Blazor.Diagram.Overview, NOT in Syncfusion.Blazor.Diagram. Forgetting it causes CS0246:

@* ❌ Wrong — SfDiagramOverviewComponent not found without the Overview namespace *@
@using Syncfusion.Blazor.Diagram

@* ✅ Correct — both namespaces required *@
@using Syncfusion.Blazor.Diagram
@using Syncfusion.Blazor.Diagram.Overview

⚠️ SourceID must exactly match the ID set on SfDiagramComponent — the ID is NOT auto-generated; you must set it explicitly. A mismatch (including case) renders the overview empty:

@* ❌ Wrong — ID not set on the diagram; SourceID has nothing to link to *@
<SfDiagramComponent Width="100%" Height="500px" Nodes="@_nodes" />
<SfDiagramOverviewComponent SourceID="myDiagram" Height="150px" />

@* ✅ Correct — ID set on diagram, SourceID matches exactly *@
<SfDiagramComponent ID="myDiagram" Width="100%" Height="500px" Nodes="@_nodes" />
<SfDiagramOverviewComponent SourceID="myDiagram" Height="150px" />

⚠️ Do NOT nest SfDiagramOverviewComponent inside SfDiagramComponent — the overview is a sibling component rendered outside the diagram markup.