我们知道Rich text或Word 或VB的程式撰写环境，可以将Mouse移到Select起来的文字
按Mouse左键做拖曳移动的功能，後来想，TextBox能不能做呢？这可真的吃了不少苦头
，这个程式模拟其做法，但主要的精神是在於对TextBox的了解。

　　首先，TextBox中当选取一段文字之後，我们只要按Mosue，便使Select的区域失效，且
可能进入另外的一个Select域，故第一件事是如何在有Select的区域时，使这动作失效；
的作法是在MouseUp时Check一下有没有选取文字，如果有，就使用SubClass的技术，拦截
Mouse的左键，所以当我们按左键时，不会再有选取文字又不见了的情况。

　　第二，我们没有按下Mouse，那如何得知Mouse所在的地方到底是TextBox的哪个字呢，所幸
有EM_CHARFROMPOS这个讯息可Send给textBox，其传回值的HiWord 得该字元是在第几行
0为base，LowWord是该字元在TextBox中的位置(含换行与LineFeed)，因而我们可以单
由MouseMove便得知何时Mouse要是箭号，何时是内定I形的Mouse。当然想得知Mouse所在
可以透过Mouse Event的X, Y座标，但是它们是以Twips为单位，而另外也可以用GetCursorPos()
来得知Mouse的位置，但这是相对於萤幕者，EMCHARFROMPOS的讯息需要的是相对於TextBox
的座标，有许多种方法可以完成这转换，但我选ScreenToClient()这个API，比较直接。

　　第叁，Caret如何隐藏呢？使用HideCaret可完成，但这个Function只能呼叫一次，以便
下回 ShowCaret()时可以将Caret Show出来，这是因为呼叫2次的HideCaret时，也要呼
叫2次的ShowCaret才能使Caret出现。另设定Caret的SetCaretPos() API只是令Caret出现
在什麽地，但如果您KeyIn任何字时，仍出现在原来之地方，而不是方才设定之处，而
要用EM_SETSEL的Message才能设定KeyIn的位置是Caret的位置。

　　另有一个取得textbox中第charindex个字元，在textbox中Mouse的位置(textbox的左上角为原点)
pos = SendMessage(hwnd, EM_POSFROMCHAR, charindex, 0)
my = pos \ 2 ^ 16 'Y座标
mx = pos Mod 2 ^ 16 'X座标

　　这个程式的重点便是上面所写的，其他是苦功

'以下在.Bas
'注:本程式之所以要用一个变数来存Caret是否被隐藏，原因是：当HideCaret()呼叫N次
'便得呼叫N次 ShowCaret()来复原，反之亦然，所以程式中，用一个变数来确认Hide/Show
'的动作只做一次
Option Explicit

Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" _
  (ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA" _
  (ByVal hwnd As Long, ByVal nIndex As Long) As Long
Declare Function CallWindowProc Lib "user32" Alias "CallWindowProcA" _
  (ByVal lpPrevWndFunc As Long, ByVal hwnd As Long, ByVal Msg As Long, _
   ByVal wParam As Long, ByVal lParam As Long) As Long

Public Const GWL_WNDPROC = (-4)
Public Const WM_MOUSEMOVE = &H200
Public Const WM_RBUTTONDOWN = &H204
Public Const WM_LBUTTONDOWN = &H201
Public Const WM_CUT = &H300
Public Const WM_PASTE = &H302
Public Const EM_POSFROMCHAR = 214
Public Const EM_CHARFROMPOS = 215
Public Const EM_SETSEL = &HB1
Public Const EM_GETSEL = &HB0
Public Const EM_SCROLL = &HB5
Public Const EM_LINEFROMCHAR = &HC9
Public Const EM_LINEINDEX = &HBB
Public Const EM_LINESCROLL = &HB6

Public Const SB_LINEDOWN = 1
Public Const SB_LINEUP = 0

Type POINTAPI
        X As Long
        Y As Long
End Type
Type RECT
        Left As Long
        Top As Long
        Right As Long
        Bottom As Long
End Type
Declare Function GetWindowRect Lib "user32" (ByVal hwnd As Long, lpRect As RECT) As Long
Declare Function GetClientRect Lib "user32" (ByVal hwnd As Long, lpRect As RECT) As Long


Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
Declare Function HideCaret Lib "user32" (ByVal hwnd As Long) As Long
Declare Function ShowCaret Lib "user32" (ByVal hwnd As Long) As Long
Declare Function SetCaretPos Lib "user32" (ByVal X As Long, ByVal Y As Long) As Long
Declare Function GetCursorPos Lib "user32" (lpPoint As POINTAPI) As Long
Declare Function ScreenToClient Lib "user32" (ByVal hwnd As Long, lpPoint As POINTAPI) As Long


Private SelEnd As Long '存TextBox Mark起来的起点
Private SelST As Long  '存textBix Mark起来的终点
Private CaretHide As Boolean '存Caret是否被隐藏
Private CanPaste As Boolean '存是否处於可以Paste的状态
Public preWinProc As Long
'取得Mouse所在的字元在TextBox中的位置
Public Function GetCharIndex(ByVal hwnd As Long, Optional CharLineNo As Long) As Long
Dim mx As Integer, my As Integer
Dim wParam As Long, lParam As Long
Dim i As Long
Dim pos As Long, pt As POINTAPI

Call GetCursorPos(pt)  '取得相对Screen的Mouse之位置
i = ScreenToClient(hwnd, pt) '将Mouse位置转换成相对於TextBox的位置
mx = pt.X
my = pt.Y
If mx < 0 Then mx = 0
If my < 0 Then my = 0
lParam = mx + 2 ^ 16 * my
wParam = 0
i = SendMessage(hwnd, EM_CHARFROMPOS, 0, lParam)
If Not IsMissing(CharLineNo) Then
   CharLineNo = i \ 2 ^ 16 '取得该字元是在第几行,0为base
End If
GetCharIndex = i Mod 2 ^ 16 '传回该字元是在textBox中的第几个字,0为base
End Function

Public Sub SetCaretPosition(ByVal hwnd As Long)
   Dim mx As Long, my As Long, pos As Long
   Dim charindex As Long
   Dim pt As POINTAPI, i As Long
   Dim rect5 As RECT, rect6 As RECT
   charindex = GetCharIndex(hwnd)
   '取得textbox中第charindex个字元，在textbox中Mouse的位置(textbox的左上角为点
   pos = SendMessage(hwnd, EM_POSFROMCHAR, charindex, 0)
   my = pos \ 2 ^ 16
   mx = pos Mod 2 ^ 16
   '设定Caret出现的位置，但只是显示的位置，实际keyin进去的字出现的地方没因而更动
   Call SetCaretPos(mx, my)
   '取得Mouse所在之座标(Screen左上角为原点)
   Call GetCursorPos(pt)
   '取得TextBox的萤幕座标(Screen左上角为原点)
   Call GetWindowRect(hwnd, rect6)
   '取得TextBox可keyin字的区域大小(textBox左上角为原点)
   Call GetClientRect(hwnd, rect5)
   '取得textbox Client区域相对Screen的座标
   rect5.Left = rect6.Left
   rect5.Right = rect5.Right + rect6.Left
   rect5.Top = rect6.Top
   rect5.Bottom = rect5.Bottom + rect6.Top
   'Mouse移到四个边时，自动scroll，就算不必Scroll时也可呼叫，只是不会有作用
   If pt.Y <= rect5.Top + 3 Then
      i = SendMessage(hwnd, EM_SCROLL, SB_LINEUP, 0)
   End If
   If pt.Y >= rect5.Bottom - 3 Then
      Call SendMessage(hwnd, EM_SCROLL, SB_LINEDOWN, 0)
   End If
   If pt.X <= rect5.Left + 3 Then
       i = SendMessage(hwnd, EM_LINESCROLL, -1, 0)
   End If
   If pt.X >= rect5.Right - 3 Then
       Call SendMessage(hwnd, EM_LINESCROLL, 1, 0)
   End If
End Sub

'设定Mouse的形状
Public Sub SetMouseShap(hwnd As Long, ByVal Button As Integer)
Dim charindex As Long
Dim i As Long
If preWinProc <> 0 Then
   If Button = 1 Then
      Screen.ActiveControl.MousePointer = 99
      Screen.ActiveControl.MouseIcon = LoadPicture("dragmove.cur")
      '请自行设定dragmove.cur的位置
      Call SetCaretPosition(hwnd)
      Exit Sub
   End If
  charindex = GetCharIndex(hwnd)
  '设定Mouse移过mark的区块时，Mouse变箭号
  If charindex >= SelST And charindex <= SelEnd Then
     If Button = 0 Then
        Screen.ActiveControl.MousePointer = 1
     End If
  Else
     Screen.ActiveControl.MousePointer = 0
  End If
End If
End Sub

Public Function wndproc(ByVal hwnd As Long, ByVal Msg As Long, _
                         ByVal wParam As Long, ByVal lParam As Long) As Long
'以下程式会截取mouse move，处理完後，再将之送往原来的Window Procedure
Dim charindex As Long
Dim i As Long
If Msg = WM_LBUTTONDOWN Then
    If CaretHide Then
       Call ShowCaret(hwnd)
       CaretHide = False
    End If
    If SelEnd - SelST <> 0 Then
       charindex = GetCharIndex(hwnd)
       If charindex >= SelST And charindex <= SelEnd Then
          Call SetCaretPosition(hwnd)
          Screen.ActiveControl.MousePointer = 99
          Screen.ActiveControl.MouseIcon = LoadPicture("c:\tmp2\dragmove.cur")
          CanPaste = True
          Exit Function
       End If
    End If
End If
wndproc = CallWindowProc(preWinProc, hwnd, Msg, wParam, lParam)
End Function

Public Sub MoveText(ByVal hwnd As Long, CanFree As Boolean)
Dim i As Long, sellen As Long, charindex As Long
sellen = SelEnd - SelST
'如果Caret落在mark起来之处则不处理
charindex = GetCharIndex(hwnd)
If charindex >= SelST And charindex <= SelEnd Then
   CanFree = False
   Exit Sub
End If
Call SendMessage(hwnd, WM_CUT, 0, 0) '将Mark起来的地方Cut掉
Dim setpos As Long
If charindex < SelST Then
   setpos = charindex
Else
   If charindex > SelEnd Then setpos = charindex - sellen
End If
'设定Caret新位置，此时Keyin进去的字才真的会在此位置出现，使用SetCaretPos()则不行
Call SendMessage(hwnd, EM_SETSEL, setpos, setpos)
Call SendMessage(hwnd, WM_PASTE, 0, 0)

End Sub
Public Sub SetHook(ByVal hwnd As Long, ByVal Button As Integer)
Dim ret As Long
Dim i As Long
Dim charindex As Long
If Button = 1 Then
    If Screen.ActiveControl.SelLength > 0 Then
       If preWinProc = 0 Then
          '记录原本的Window Procedure的位址
          preWinProc = GetWindowLong(hwnd, GWL_WNDPROC)
          ret = SetWindowLong(hwnd, GWL_WNDPROC, AddressOf wndproc)
          Call HideCaret(hwnd)
          CaretHide = True
          CanPaste = False
          '取得Mark起来的区域之Start, End之Index，之所以不用Text.SelStart
          '与Text.SelLength来做的原因是：vb对之的度量是字元为单位，但API
          '的其他呼叫都以Byte为单位，我如此做，省得中间的转换
          i = SendMessage(hwnd, EM_GETSEL, 0, 0)
          SelEnd = i \ 2 ^ 16
          SelST = i Mod 2 ^ 16
       Else
        Dim CanFree As Boolean
        CanFree = True
        If CanPaste Then
           Call MoveText(hwnd, CanFree)
        End If
        If CanFree Then Call FreeHook(hwnd)
       End If
    Else
       If preWinProc <> 0 Then
          Call FreeHook(hwnd)
       End If
    End If
End If
End Sub
Public Sub FreeHook(ByVal hwnd As Long)
Dim ret As Long
If preWinProc <> 0 Then
   ret = SetWindowLong(hwnd, GWL_WNDPROC, preWinProc)
End If
preWinProc = 0
Screen.ActiveControl.MousePointer = 0
If CaretHide Then
   Call ShowCaret(hwnd)
   CaretHide = False
End If
End Sub
Public Sub GetCaretPos(ByVal hwnd5 As Long, lineno As Long, colno As Long)
Dim i As Long, j As Long
Dim lParam As Long, wParam As Long
Dim k As Long
i = SendMessage(hwnd5, EM_GETSEL, wParam, lParam)
j = i / 2 ^ 16  '取得目前Caret所在前面有多少个byte
lineno = SendMessage(hwnd5, EM_LINEFROMCHAR, j, 0) '取得前面有多少行
lineno = lineno + 1
k = SendMessage(hwnd5, EM_LINEINDEX, -1, 0)
'取得目前caret所在行前面有多少个byte
colno = j - k + 1
End Sub



>
'以下在Form
Private Sub Text1_LostFocus()
Call FreeHook(Text1.hwnd)
End Sub

Private Sub Text1_KeyDown(KeyCode As Integer, Shift As Integer)
Call FreeHook(Text1.hwnd)
End Sub

Private Sub Text1_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single)
  Call SetMouseShap(Text1.hwnd, Button)
End Sub

Private Sub Text1_MouseUp(Button As Integer, Shift As Integer, X As Single, Y As Single)
  Call SetHook(Text1.hwnd, Button)
End Sub