History

The RadDocument class can track the history of any actions taken against its content. In this way it allows an undo and redo functionality to be easily implemented. The history is implemented via the DocumentHistory class and the RadDocument exposes the History property of this type. The RadRichTextBox control automatically adds and removes items from the history, when its API methods get called, but you are allowed to manually work with the history as well.

To learn more about the DocumentHistory API, read here.

This topic will explain you how to:

• Enable/Disable History
• Clear History
• Undo/Redo Actions
• Change History Depth
• Preserve History Using RadDocumentEditor
• UndoGroup

Enable/Disable History

You can enable or disable the history for the RadDocument via the Enabled property of the DocumentHistory.

Disable history

this.radRichTextBox.Document.History.Enabled = false; 

Me.radRichTextBox.Document.History.Enabled = False 

Clear History

To clear the history you just have to call the Clear method of the DocumentHistory class.

Clearing the history

this.radRichTextBox.Document.History.Clear(); 

Me.radRichTextBox.Document.History.Clear() 

Undo/Redo Actions

To undo and redo some actions, you can call the Undo and Redo methods of RadRichTextBox.

Using the Redo and Undo methods of RadRichTextBox

private void UndoAction() 
{ 
    this.radRichTextBox.Undo(); 
} 
private void RedoAction() 
{ 
    this.radRichTextBox.Redo(); 
} 

Private Sub UndoAction() 
 Me.radRichTextBox.Undo() 
End Sub 
Private Sub RedoAction() 
 Me.radRichTextBox.Redo() 
End Sub 

Change History Depth

To change the history capacity you have to set the desired value of the Depth property of the DocumentHistory. The default one is 1000.

Changing the history depth

this.radRichTextBox.Document.History.Depth = 500; 

Me.radRichTextBox.Document.History.Depth = 500 

Preserve History Using RadDocumentEditor

The methods of the RadDocument class do not register in the undo/redo stack. Once a method is invoked, the history stack will be cleared and the users will no longer be able to undo/redo previous actions. Due to this and for some other factors, the RadDocumentEditor class was introduced. You can find detailed information about it here.

UndoGroup

The RadDocumentEditor control allows you to group several methods so that they are added to the Undo/Redo stack as a single item. To do so, you can use the BeginUndoGroup and EndUndoGroup methods.

Using the BeginUndoGroup and EndUndoGroup methods

documentEditor.BeginUndoGroup();  
 
if (documentEditor.Document.CaretPosition.IsPositionInsideTable)  
{  
    documentEditor.InsertTableRow();  
    documentEditor.InsertTableRow();  
    documentEditor.InsertTableRow();  
    documentEditor.Document.Selection.Clear();  
}  
 
documentEditor.EndUndoGroup("Insert three table rows");  

documentEditor.BeginUndoGroup()  
 
If documentEditor.Document.CaretPosition.IsPositionInsideTable Then  
    documentEditor.InsertTableRow()  
    documentEditor.InsertTableRow()  
    documentEditor.InsertTableRow()  
    documentEditor.Document.Selection.Clear()  
End If  
 
documentEditor.EndUndoGroup("Insert three table rows")  

To cancel the execution of the undo group and prevent it from being recorded to the history, you can use the CancelUndoGroup method.

Using the CancelUndoGroup method

documentEditor.BeginUndoGroup();  
 
if (documentEditor.Document.CaretPosition.IsPositionInsideTable)  
{  
    documentEditor.InsertTableRow();  
    documentEditor.InsertTableRow();  
    documentEditor.InsertTableRow();  
    documentEditor.Document.Selection.Clear();  
}  
 
documentEditor.CancelUndoGroup();  

documentEditor.BeginUndoGroup()  
 
If documentEditor.Document.CaretPosition.IsPositionInsideTable Then  
    documentEditor.InsertTableRow()  
    documentEditor.InsertTableRow()  
    documentEditor.InsertTableRow()  
    documentEditor.Document.Selection.Clear()  
End If  
 
documentEditor.CancelUndoGroup()  

One thing to note here is that it is not possible to remove some actions from the undo history altogether, i.e. you cannot perform an action without it getting registered in the Undo/Redo stack. In most cases, however, this is sufficient, as you can group the operations that you do not want to name and show explicitly to the end user with the ones that have been user-initiated and are expected by the person modifying the content of RadRichTextBox.

See Also

• Selection
• Positioning