窗口句柄
在Windows中，句柄是一个系统内部数据结构的引用。例如，当你操作一个窗口，或说是一个Delphi窗体时，系统会给你一个该窗口的句柄，系统会通知你：你正在操作142号窗口，就此，你的应用程序就能要求系统对142号窗口进行操作——移动窗口、改变窗口大小、把窗口极小化为图标，等等。实际上许多Windows API函数把句柄作为它的第一个参数，如GDI（图形设备接口）句柄、菜单句柄、实例句柄、位图句柄等等，不仅仅局限于窗口函数。 
换句话说，句柄是一种内部代码，通过它能引用受系统控制的特殊元素，如窗口、位图、图标、内存块、光标、字体、菜单等等。 
案例：获取窗口句柄 
案例说明 
本例实现窗口句柄的获取。 
实现过程 
Private Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long) As Long 
Private Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long 
Private Declare Function SetLayeredWindowAttributes Lib "user32" (ByVal hwnd As Long, ByVal crKey As Long, ByVal bAlpha As Byte, ByVal dwFlags As Long) As Long 
Private Const WS_EX_LAYERED = &H80000 
Private Const GWL_EXSTYLE = (-20) 
Private Const LWA_ALPHA = &H2 
Private Sub Form_Activate() 
On Error Resume Next 
For i = 0 To 150 Step 2.5 
SetLayeredWindowAttributes Me.hwnd, 0, i, LWA_ALPHA 
DoEvents 
Next i 
End Sub 
Private Sub Form_load() 
Dim rtn As Long 
rtn = GetWindowLong(Me.hwnd, GWL_EXSTYLE) 
rtn = rtn Or WS_EX_LAYERED 
SetWindowLong Me.hwnd, GWL_EXSTYLE, rtn 
SetLayeredWindowAttributes Me.hwnd, 0, 0, LWA_ALPHA 
End Sub