CommandManager

Undo/redo system using the command pattern. Provides unlimited history for graph operations.

Overview

CommandManager automatically tracks graph operations and provides undo/redo functionality. All node and edge operations are recorded.

Properties

Property	Type	Description
Graph	FlowGraph	Associated graph
UndoCount	int	Number of operations in undo stack
RedoCount	int	Number of operations in redo stack

Methods

UndoAsync

Undoes the last operation.

Signature: ValueTask UndoAsync()

await graph.CommandManager.UndoAsync();

RedoAsync

Redoes the last undone operation.

Signature: ValueTask RedoAsync()

await graph.CommandManager.RedoAsync();

ClearStacks

Clears the undo and redo stacks.

Signature: void ClearStacks()

graph.CommandManager.ClearStacks();

Events

UndoRedoStackChanged

Fired when the undo/redo stacks change.

Type: EventHandler<EventArgs>

graph.CommandManager.UndoRedoStackChanged += (sender, e) =>
{
    UpdateUI();
};

Automatic Tracking

Commands are automatically tracked for:

Node creation
Node removal
Edge creation
Edge removal

// These operations are automatically tracked:
await graph.CreateNodeAsync<MyNode>(100, 100, []);  // Tracked
await graph.RemoveNodeAsync(nodeId);                // Tracked
await graph.ConnectAsync(from, to, "Out", "In");   // Tracked
await graph.RemoveEdgeAsync(edgeId);                // Tracked

UI Integration

Undo/Redo Buttons

<button @onclick="Undo" 
        disabled="@(graph.CommandManager.UndoCount == 0)">
    ↶ Undo (@graph.CommandManager.UndoCount)
</button>

<button @onclick="Redo" 
        disabled="@(graph.CommandManager.RedoCount == 0)">
    ↷ Redo (@graph.CommandManager.RedoCount)
</button>

@code {
    async Task Undo()
    {
        await graph.CommandManager.UndoAsync();
    }

    async Task Redo()
    {
        await graph.CommandManager.RedoAsync();
    }
}

Keyboard Shortcuts

FlowCanvas automatically handles Ctrl+Z / Ctrl+Y:

// Built-in keyboard shortcuts:
// Ctrl+Z or Cmd+Z → Undo
// Ctrl+Y or Cmd+Shift+Z → Redo

Custom keyboard handling:

<FlowCanvas Graph="graph" OnKeyDown="HandleKeyDown">
    ...
</FlowCanvas>

@code {
    async Task HandleKeyDown(KeyboardEventArgs e)
    {
        if (e.CtrlKey || e.MetaKey)
        {
            if (e.Key == "z" && !e.ShiftKey)
            {
                await graph.CommandManager.UndoAsync();
            }
            else if (e.Key == "y" || (e.Key == "z" && e.ShiftKey))
            {
                await graph.CommandManager.RedoAsync();
            }
        }
    }
}

Complete Example

@using FlowState.Components
@using FlowState.Models

<div class="toolbar">
    <button class="toolbar-btn" 
            @onclick="Undo"
            disabled="@(!CanUndo)">
        ↶ Undo
    </button>
    
    <button class="toolbar-btn" 
            @onclick="Redo"
            disabled="@(!CanRedo)">
        ↷ Redo
    </button>
    
    <div class="history-info">
        History: @graph.CommandManager.UndoCount operations
    </div>
</div>

<FlowCanvas Graph="graph" Height="calc(100vh - 60px)" Width="100vw">
    <BackgroundContent>
        <FlowBackground class="grid-bg"/>
    </BackgroundContent>
</FlowCanvas>

@code {
    FlowGraph graph = new();
    
    bool CanUndo => graph.CommandManager.UndoCount > 0;
    bool CanRedo => graph.CommandManager.RedoCount > 0;

    protected override void OnInitialized()
    {
        // Subscribe to stack changes to update UI
        graph.CommandManager.UndoRedoStackChanged += (s, e) =>
        {
            StateHasChanged();
        };
        
        graph.RegisterNode<MyNode>();
    }

    async Task Undo()
    {
        if (CanUndo)
        {
            await graph.CommandManager.UndoAsync();
        }
    }

    async Task Redo()
    {
        if (CanRedo)
        {
            await graph.CommandManager.RedoAsync();
        }
    }
}

Read-Only Mode

Commands are not tracked in read-only mode:

await canvas.SetReadOnlyAsync(true);

// Operations in read-only mode are not tracked
// Undo/redo are disabled

Clearing History

Clear the command history when appropriate:

// After loading a new graph
await graph.DeserializeAsync(json);
graph.CommandManager.ClearStacks();

// After clearing the canvas
await graph.ClearAsync();
// Stacks are automatically cleared

Stack Limits

There is no built-in limit to the undo/redo stacks. For memory-constrained scenarios, you might want to implement a custom limit.

Suppressing Commands

Operations can suppress command tracking:

// Internal use - normally not needed in user code
await graph.CreateNodeAsync<MyNode>(
    100, 100, 
    [], 
    suppressEvent: false,
    suppressAddingToCommandStack: true  // Don't track
);

Command Types

The following command types are automatically tracked:

NodeAddedCommand - Node creation
NodeRemovedCommand - Node deletion (includes connected edges)
EdgeAddedCommand - Edge creation
EdgeRemovedCommand - Edge deletion