怎样实现“撤消”功能

[wangsanxia]

我是个初学者，在编记事本和画图。不知道在这两个程序中怎样分别实现菜单中“撤消”选项的功能，允许用户撤消上次的操作。

[lhxtx]

RichTextBox.Undo

[wangsanxia]

RichTextBox中没有Undo方法啊

[chenke_ikari]

Private Sub CmdUndo_Click()
Select Case CurrentTextBox
Case "TxtCompany":
TxtCompany(CurrentLine).SetFocus
SendKeys Chr(27) '发送"撤销"命令到当前输入框
Case "TxtProducer":
TxtProducer(CurrentLine).SetFocus
SendKeys Chr(27)
Case "TxtProduct":
TxtProduct(CurrentLine).SetFocus
SendKeys Chr(27)
Case "TxtModel":
TxtModel(CurrentLine).SetFocus
SendKeys Chr(27)
Case "TxtPrice":
TxtPrice(CurrentLine).SetFocus
SendKeys Chr(27)
Case "TxtTime":
TxtTime(CurrentLine).SetFocus
SendKeys Chr(27)
Case "TxtComment":
TxtComment(CurrentLine).SetFocus
SendKeys Chr(27)
End Select
End Sub

SendKeys Chr(27)即Windows中的Ctrl+Z

[hisofty]

可以直接发送wm_undo消息

[bydisplay]

Declare Function SendMessage Lib"user"(ByVal hWnd As Integer,ByVal wMsg As Integer,wParam As Integer,lparam As Any) As Long
Global Const WM_USER=&h400
Global Const EM_UNDO=WM_USER+23
UndoResult=SendMessage(myControl.hWnd,EM_UNDO,0,0)

[wangsanxia]

在记事本程序中，发送发送wm_undo消息会将所有的字符消除，而且莫名其妙的出现字符0，我想每次撤消只清楚上次的操作。

[lwzlemon]

mark