Dim ret As Long
Private Sub Command1_Click()
Call SendMessage(Me.Hwnd, WM_MYMSG, 0, 0)
End Sub
Private Sub Form_Load()
preWinProc = GetWindowLong(Me.Hwnd, GWL_WNDPROC)
ret = SetWindowLong(Me.Hwnd, GWL_WNDPROC, AddressOf WndProc)
End Sub
Private Sub Form_Unload(Cancel As Integer)
ret& = SetWindowLong(Me.Hwnd, GWL_WNDPROC, preWinProc)
End Sub
模块代码:
Option Explicit
Public Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal Hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
Public Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA" (ByVal Hwnd As Long, ByVal nIndex As Long) As Long
Public Declare Function DefWindowProc Lib "user32" Alias "DefWindowProcA" (ByVal Hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
Public 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 Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal Hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long
Public Const WM_USER = &H400
Public Const GWL_WNDPROC = (-4)
Public Const WM_MYMSG = WM_USER + 100
Public Const WM_RBUTTONDOWN = &H204
Public preWinProc As Long
Public Function WndProc(ByVal Hwnd As Long, ByVal Msg As Long, _
ByVal wParam As Long, ByVal lParam As Long) As Long
If Msg = WM_MYMSG Then
MsgBox "Here is my difine message"
Else
WndProc = CallWindowProc(preWinProc, Hwnd, Msg, wParam, lParam)
End If
RaiseEvent Statment Example
The following example uses events to count off seconds during a demonstration of the fastest 100 meter race. The code illustrates all of the event-related methods, properties, and statements, including the RaiseEvent statement.
The class that raises an event is the event source, and the classes that implement the event are the sinks. An event source can have multiple sinks for the events it generates. When the class raises the event, that event is fired on every class that has elected to sink events for that instance of the object.
The example also uses a form (Form1) with a button (Command1), a label (Label1), and two text boxes (Text1 and Text2). When you click the button, the first text box displays "From Now" and the second starts to count seconds. When the full time (9.84 seconds) has elapsed, the first text box displays "Until Now" and the second displays "9.84"
The code for Form1 specifies the initial and terminal states of the form. It also contains the code executed when events are raised.
Option Explicit
Private WithEvents mText As TimerState
Private Sub Command1_Click()
Text1.Text = "From Now"
Text1.Refresh
Text2.Text = "0"
Text2.Refresh
Call mText.TimerTask(9.84)
End Sub
Private Sub Form_Load()
Command1.Caption = "Click to Start Timer"
Text1.Text = ""
Text2.Text = ""
Label1.Caption = "The fastest 100 meters ever run took this long:"
Set mText = New TimerState
End Sub
Private Sub mText_ChangeText()
Text1.Text = "Until Now"
Text2.Text = "9.84"
End Sub
Private Sub mText_UpdateTime(ByVal dblJump As Double)
Text2.Text = Str(Format(dblJump, "0"))
DoEvents
End Sub
The remaining code is in a class module named TimerState. Included among the commands in this module are the Raise Event statements.
Option Explicit
Public Event UpdateTime(ByVal dblJump As Double)
Public Event ChangeText()
Public Sub TimerTask(ByVal Duration As Double)
Dim dblStart As Double
Dim dblSecond As Double
Dim dblSoFar As Double
dblStart = Timer
dblSoFar = dblStart
Do While Timer < dblStart + Duration
If Timer - dblSoFar >= 1 Then
dblSoFar = dblSoFar + 1
RaiseEvent UpdateTime(Timer - dblStart)
End If
Loop