如何用VB实现半透明控件

    本代码演示半透明控件的实现过程。如果是自定义控件，实现起来非常简单，如果是系统控件，则要复杂一些。如果系统控件支持属主画，跟自定义控件思路完全是一样的，只不过代码是写在子类化的过程里。 

    先建一个标准EXE工程，然后添加一个用户控件，把以下代码复制到控件代码中，再把此控件放置到Form1上。

Option Explicit Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (Destination As Any, Source As Any, ByVal Length As Long) Private Declare Function GetClientRect Lib "user32" (ByVal hwnd As Long, lpRect As RECT) As Long Private Declare Function ClientToScreen Lib "user32" (ByVal hwnd As Long, lpPoint As POINTAPI) As Long Private Declare Function ScreenToClient Lib "user32" (ByVal hwnd As Long, lpPoint As POINTAPI) As Long Private Declare Function SetRect Lib "user32" (lpRect As RECT, ByVal X1 As Long, ByVal Y1 As Long, ByVal X2 As Long, ByVal Y2 As Long) As Long Private Declare Function OffsetRect Lib "user32" (lpRect As RECT, ByVal X As Long, ByVal Y As Long) As Long Private Type POINTAPI X As Long Y As Long End Type Private Type RECT Left As Long Top As Long Right As Long Bottom As Long End Type Private Declare Function DrawText Lib "user32" Alias "DrawTextA" (ByVal hdc As Long, ByVal lpStr As String, ByVal nCount As Long, lpRect As RECT, ByVal wFormat As Long) As Long Private Const DT_SINGLELINE = &H20 Private Const DT_CENTER = &H1 Private Const DT_VCENTER = &H4 Private Declare Function GetDC Lib "user32" (ByVal hwnd As Long) As Long Private Declare Function ReleaseDC Lib "user32" (ByVal hwnd As Long, ByVal hdc As Long) As Long Private Declare Function CreateCompatibleDC Lib "gdi32" (ByVal hdc As Long) As Long Private Declare Function DeleteDC Lib "gdi32" (ByVal hdc As Long) As Long Private Declare Function CreateCompatibleBitmap Lib "gdi32" (ByVal hdc As Long, ByVal nWidth As Long, ByVal nHeight As Long) As Long Private Declare Function SelectObject Lib "gdi32" (ByVal hdc As Long, ByVal hObject As Long) As Long Private Declare Function DeleteObject Lib "gdi32" (ByVal hObject As Long) As Long Private Declare Function ShowWindow Lib "user32" (ByVal hwnd As Long, ByVal nCmdShow As Long) As Long Private Const SW_SHOW = 5 Private Const SW_HIDE = 0 Private Declare Function BitBlt Lib "gdi32" (ByVal hDestDC As Long, ByVal X As Long, ByVal Y As Long, ByVal nWidth As Long, ByVal nHeight As Long, ByVal hSrcDC As Long, ByVal xSrc As Long, ByVal ySrc As Long, ByVal dwRop As Long) As Long Private Declare Function AlphaBlend Lib "msimg32" (ByVal hDestDC As Long, ByVal X As Long, ByVal Y As Long, ByVal nWidth As Long, ByVal nHeight As Long, ByVal hSrcDC As Long, ByVal xSrc As Long, ByVal ySrc As Long, ByVal widthSrc As Long, ByVal heightSrc As Long, ByVal blendFunct As Long) As Boolean Dim m_hMemDC As Long Dim m_hMemBmp As Long, m_hMemBmpPrev As Long Dim m_rcControl As RECT Private Sub UserControl_Initialize() UserControl.AutoRedraw = True UserControl.BackColor = vbRed m_hMemDC = CreateCompatibleDC(UserControl.hdc) End Sub Private Sub UserControl_Terminate() If m_hMemBmp <> 0 Then DeleteObject SelectObject(m_hMemDC, m_hMemBmpPrev) End If DeleteDC m_hMemDC End Sub Public Sub Translucence() Dim hdc As Long Dim tPt As POINTAPI '获得控件当前位置和大小 ClientToScreen UserControl.hwnd, tPt ScreenToClient UserControl.ContainerHwnd, tPt Call GetClientRect(UserControl.hwnd, m_rcControl) OffsetRect m_rcControl, tPt.X, tPt.Y '创建一幅内存位图 If m_hMemBmp <> 0 Then DeleteObject (SelectObject(m_hMemDC, m_hMemBmpPrev)) End If m_hMemBmp = CreateCompatibleBitmap(UserControl.hdc, m_rcControl.Right, m_rcControl.Bottom) m_hMemBmpPrev = SelectObject(m_hMemDC, m_hMemBmp) '隐藏控件 ShowWindow UserControl.hwnd, SW_HIDE DoEvents '保存控件容器的图像到内存位图中 Dim hDesktopDC As Long hDesktopDC = GetDC(UserControl.hwnd) BitBlt m_hMemDC, 0, 0, m_rcControl.Right, m_rcControl.Bottom, hDesktopDC, 0, 0, vbSrcCopy ReleaseDC 0, hDesktopDC '通过alpha效果进行半透明渲染 UserControl.AutoRedraw = True AlphaBlend m_hMemDC, 0, 0, m_rcControl.Right, m_rcControl.Bottom, UserControl.hdc, 0, 0, m_rcControl.Right, m_rcControl.Bottom, 5242880 UserControl.AutoRedraw = False '显示控件 ShowWindow UserControl.hwnd, SW_SHOW '将渲染后的结果复制到控件中 BitBlt UserControl.hdc, 0, 0, m_rcControl.Right, m_rcControl.Bottom, m_hMemDC, 0, 0, vbSrcCopy End Sub Private Sub UserControl_Paint() BitBlt UserControl.hdc, 0, 0, m_rcControl.Right, m_rcControl.Bottom, m_hMemDC, 0, 0, vbSrcCopy End Sub

    在Form1的Form_Activate事件里输入以下代码：

Private Sub Form_Activate() Me.UserControl11.Translucence End Sub

    最后，你将看到一个粉红色半透明的方块，该方块就是你所需要的半透明的控件。至于控件的其它功能，读者可以自行扩展。