TextBoxBase.ClearUndo Method ()
Clears information about the most recent operation from the undo buffer of the text box.
Assembly: System.Windows.Forms (in System.Windows.Forms.dll)
You can use this method to prevent an undo operation from repeating, based on the state of your application.
The following code example uses TextBox, a derived class. It provides Click event handlers for MenuItem objects that perform Cut, Copy, Paste, and Undo operations. This example requires that a TextBox control named textBox1 has been created.
Private Sub Menu_Copy(sender As System.Object, e As System.EventArgs) ' Ensure that text is selected in the text box. If textBox1.SelectionLength > 0 Then ' Copy the selected text to the Clipboard. textBox1.Copy() End If End Sub Private Sub Menu_Cut(sender As System.Object, e As System.EventArgs) ' Ensure that text is currently selected in the text box. If textBox1.SelectedText <> "" Then ' Cut the selected text in the control and paste it into the Clipboard. textBox1.Cut() End If End Sub Private Sub Menu_Paste(sender As System.Object, e As System.EventArgs) ' Determine if there is any text in the Clipboard to paste into the text box. If Clipboard.GetDataObject().GetDataPresent(DataFormats.Text) = True Then ' Determine if any text is selected in the text box. If textBox1.SelectionLength > 0 Then ' Ask user if they want to paste over currently selected text. If MessageBox.Show("Do you want to paste over current selection?", _ "Cut Example", MessageBoxButtons.YesNo) = DialogResult.No Then ' Move selection to the point after the current selection and paste. textBox1.SelectionStart = textBox1.SelectionStart + _ textBox1.SelectionLength End If End If ' Paste current text in Clipboard into text box. textBox1.Paste() End If End Sub Private Sub Menu_Undo(sender As System.Object, e As System.EventArgs) ' Determine if last operation can be undone in text box. If textBox1.CanUndo = True Then ' Undo the last operation. textBox1.Undo() ' Clear the undo buffer to prevent last action from being redone. textBox1.ClearUndo() End If End Sub
Available since 1.1