Undoing Text Operations

Every edit control maintains an undo flag that indicates whether an application can reverse (undo) the most recent operation on the edit control (to undo a text deletion, for example). The edit control sets the undo flag to indicate that the operation can be undone and resets it to indicate that the operation cannot be undone. An application can determine the setting of the undo flag by sending the control an EM_CANUNDO message.

An application can undo the most recent operation by sending the control an EM_UNDO message. An operation can be undone provided no other edit control operation occurs first. For example, the user can delete text, replace the text (undo the deletion), and then delete the text again (undo the replacement). The EM_UNDO message applies to both single-line and multiline edit controls and always works for single-line edit controls.

An application can reset an edit control's undo flag by sending the control an EM_EMPTYUNDOBUFFER message. Windows automatically resets the undo flag whenever an edit control receives an EM_SETHANDLE or WM_SETTEXT message. The SetDlgItemText function sends a WM_SETTEXT message.

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