Class DiagramHistoryManager

Represents the manager that handles undo and redo operations for a diagram, notifying when changes are reverted or restored.

Inheritance

System.Object

DiagramHistoryManager

Namespace: Syncfusion.Blazor.Diagram

Assembly: Syncfusion.Blazor.dll

Syntax

public class DiagramHistoryManager : ComponentBase

Remarks

The DiagramHistoryManager is crucial for maintaining the state of a diagram by allowing users to undo and redo changes.

Constructors

DiagramHistoryManager()

Initializes a new instance of the DiagramHistoryManager class.

Declaration

public DiagramHistoryManager()

Properties

CanRedo

Gets or sets a value indicating whether the history entry can be redone.

Declaration

public bool CanRedo { get; set; }

Property Value

Type
System.Boolean

Remarks

When set to true, the history manager enables reapplying the last undone action, facilitating the reinstatement of changes that were reversed, thus enhancing the flexibility of the undo-redo workflow.

CanUndo

Gets or sets a value indicating whether the history entry can be undone.

Declaration

public bool CanUndo { get; set; }

Property Value

Type
System.Boolean

Remarks

Setting this property to true allows the history manager to revert the most recent action, ensuring that accidental changes can be easily undone to restore previous states.

ChildContent

Gets or sets the child content for the history manager.

Declaration

public RenderFragment ChildContent { get; set; }

Property Value

Type
Microsoft.AspNetCore.Components.RenderFragment

Remarks

Allows customization of the history manager's content using render fragments, enabling dynamic and flexible UI updates within the diagram component. It supports customization of the user interface by defining children elements that are rendered dynamically.

CurrentEntry

Gets or sets the current entry object.

Declaration

public HistoryEntryBase CurrentEntry { get; set; }

Property Value

Type
HistoryEntryBase

Remarks

Represents the specific history entry currently active within the diagram's history stack, allowing users to query or modify the current state of the undo and redo operations.

HistoryAdding

Gets or sets a callback that occurs determining if changes should be stored in the history.

Declaration

public EventCallback<HistoryAddingEventArgs> HistoryAdding { get; set; }

Property Value

Type
Microsoft.AspNetCore.Components.EventCallback<HistoryAddingEventArgs>

Remarks

This event is triggered before a change is added to the history, allowing you to decide whether it should be committed.

Examples

<SfDiagramComponent Width="800px" Height="800px">
    <DiagramHistoryManager HistoryAdding="OnHistoryAdding"></DiagramHistoryManager>
</SfDiagramComponent>
@code
{
    private void OnHistoryAdding(HistoryAddingEventArgs args)
    {
        args.Cancel = true;
    }
}

Redo

Gets or sets the callback method that is invoked when a custom entry is in the redo stage.

Declaration

public EventCallback<HistoryEntryBase> Redo { get; set; }

Property Value

Type
Microsoft.AspNetCore.Components.EventCallback<HistoryEntryBase>

Remarks

Allows integration of custom logic during the redo operation within the diagram component, enhancing the flexibility and control over redo actions.

Examples

<SfDiagramComponent Width="800px" Height="800px">
    <DiagramHistoryManager Redo="onCustomRedo"></DiagramHistoryManager>
</SfDiagramComponent>
@code
{
    private void onCustomRedo(HistoryEntryBase entry)
    {
        Node current = entry.UndoObject.Clone() as Node;
        (entry.UndoObject as Node).AdditionalInfo[(entry.UndoObject as Node).ID] = "Description";
        entry.RedoObject = current;
    }
}

StackLimit

Gets or sets the number of history entries that can be stored on the history list to limit undo, redo stack.

Declaration

public int StackLimit { get; set; }

Property Value

Type	Description
System.Int32	An System.Int32 representing the maximum number of history entries. The default value is 0.

Remarks

This property helps control memory usage by limiting the number of actions stored in the history list for undo and redo operations.

Examples

<SfDiagramComponent Height="900px">
    <DiagramHistoryManager StackLimit="@stack" ></DiagramHistoryManager>
</SfDiagramComponent>

Undo

Gets or sets the callback method that is invoked when a custom entry is in the undo stage.

Declaration

public EventCallback<HistoryEntryBase> Undo { get; set; }

Property Value

Type
Microsoft.AspNetCore.Components.EventCallback<HistoryEntryBase>

Remarks

Allows integration of custom logic during the undo operation within the diagram component, enhancing the flexibility and control over undo actions.

Examples

<SfDiagramComponent Width="800px" Height="800px">
    <DiagramHistoryManager Undo="onCustomUndo"></DiagramHistoryManager>
</SfDiagramComponent >
@code
{
    private void onCustomUndo(HistoryEntryBase entry)
    {
        (entry.RedoObject) = entry.UndoObject.Clone() as Node;
        (entry.UndoObject as Node).AdditionalInfo[(entry.UndoObject as Node).ID] = "Start";
    }
}

Methods

BuildRenderTree(RenderTreeBuilder)

Declaration

protected override void BuildRenderTree(RenderTreeBuilder __builder)

Parameters

Type	Name	Description
Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder	__builder

Dispose()

This method releasing all unmanaged resources.

Declaration

public void Dispose()

EndGroupAction()

Ends a group action which encapsulates multiple changes for combined undo/redo operations within the Syncfusion.Blazor.Diagram.DiagramHistoryManager.Diagram.

Declaration

public void EndGroupAction()

Remarks

This method finalizes the grouping of changes, allowing them to be treated as a single action in the undo/redo sequence, thus enhancing the user's control over multiple related modifications.

Examples

// End the grouping of changes
diagram.EndGroupAction();

OnAfterRenderAsync(Boolean)

Method invoked after each time the component has been rendered.

Declaration

protected override Task OnAfterRenderAsync(bool firstRender)

Parameters

Type	Name	Description
System.Boolean	firstRender	Set to true for the first time component rendering, otherwise gets false.

Returns

Type	Description
System.Threading.Tasks.Task	A System.Threading.Tasks.Task representing any asynchronous operation.

OnInitializedAsync()

This method is invoked when the component is ready to start.

Declaration

protected override Task OnInitializedAsync()

Returns

Type
System.Threading.Tasks.Task

OnParametersSetAsync()

Method invoked when any changes in component state occur.

Declaration

protected override Task OnParametersSetAsync()

Returns

Type	Description
System.Threading.Tasks.Task	="Task".

StartGroupAction()

Initiates a group action allowing you to revert or restore multiple changes through a single undo/redo command within the Syncfusion.Blazor.Diagram.DiagramHistoryManager.Diagram.

Declaration

public void StartGroupAction()

Remarks

This method starts the grouping of changes, which is useful for managing multiple related modifications in a unified manner using undo/redo functionality.

Examples

// Start the grouping of changes 
diagram.StartGroupAction();