|
|
Pass String Data Between Applications Using SendMessage
Step-by-Step Example
[ol]Convert the string to a byte array using the CopyMemory() API. Obtain the address of the byte array using the VarPtr() intrinsic function and copy the address and length of the byte array into a COPYDATASTRUCT structure. Pass the COPYDATASTRUCT to another application using the WM_COPYDATA message, setting up the other application to receive the message. Unpack the structure on the target system using CopyMemory(), and convert the byte array back to a string using the StrConv() intrinsic function.
[/ol]
The next section shows you how to create a sample program that demonstrates passing string data from one application to another.
Steps to Create the Sample
To create this sample, you will create two separate projects; a sending project and a target project.
Create the target application:
[ol]Start a new Standard EXE project in Visual Basic. Form1 is created by default. This project will be your target application. Add a Label control to Form1. Copy the following code to the Code window of Form1: Private Sub Form_Load()
gHW = Me.hWnd
Hook
Me.Caption = "Target"
Me.Show
Label1.Caption = Hex$(gHW)
End Sub Private Sub Form_Unload(Cancel As Integer)
Unhook
End SubAdd a module to the project and paste the following code in the Module1 code window: Type COPYDATASTRUCT
dwData As Long
cbData As Long
lpData As Long
End Type Public Const GWL_WNDPROC = (-4)
Public Const WM_COPYDATA = &H4A
Global lpPrevWndProc As Long
Global gHW As Long 'Copies a block of memory from one location to another.
Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" _
(hpvDest As Any, hpvSource As Any, ByVal cbCopy As Long) Declare Function CallWindowProc Lib "user32" Alias _
"CallWindowProcA" (ByVal lpPrevWndFunc As Long, ByVal hwnd As _
Long, ByVal Msg As Long, ByVal wParam As Long, ByVal lParam As _
Long) As Long Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" _
(ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As _
Long) As Long Public Sub Hook()
lpPrevWndProc = SetWindowLong(gHW, GWL_WNDPROC, _
AddressOf WindowProc)
Debug.Print lpPrevWndProc
End Sub Public Sub Unhook()
Dim temp As Long
temp = SetWindowLong(gHW, GWL_WNDPROC, lpPrevWndProc)
End Sub Function WindowProc(ByVal hw As Long, ByVal uMsg As Long, _
ByVal wParam As Long, ByVal lParam As Long) As Long
If uMsg = WM_COPYDATA Then
Call mySub(lParam)
End If
WindowProc = CallWindowProc(lpPrevWndProc, hw, uMsg, wParam, _
lParam)
End Function Sub mySub(lParam As Long)
Dim cds As COPYDATASTRUCT
Dim buf(1 To 255) As Byte Call CopyMemory(cds, ByVal lParam, Len(cds)) Select Case cds.dwData
Case 1
Debug.Print "got a 1"
Case 2
Debug.Print "got a 2"
Case 3
Call CopyMemory(buf(1), ByVal cds.lpData, cds.cbData)
a$ = StrConv(buf, vbUnicode)
a$ = Left$(a$, InStr(1, a$, Chr$(0)) - 1)
Form1.Print a$
End Select
End SubSave the project and minimize the Visual Basic IDE.
[/ol]
Create the Sending Application:
[ol]Start a second instance of the Visual Basic IDE and create a new Standard EXE project in Visual Basic. Form1 is created by default. Add a CommandButton to Form1. Copy the following code to the Code window of Form1: Private Type COPYDATASTRUCT
dwData As Long
cbData As Long
lpData As Long
End Type Private Const WM_COPYDATA = &H4A Private Declare Function FindWindow Lib "user32" Alias _
"FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName _
As String) As Long Private Declare Function SendMessage Lib "user32" Alias _
"SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal _
wParam As Long, lParam As Any) As Long 'Copies a block of memory from one location to another.
Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" _
(hpvDest As Any, hpvSource As Any, ByVal cbCopy As Long) Private Sub Command1_Click()
Dim cds As COPYDATASTRUCT
Dim ThWnd As Long
Dim buf(1 To 255) As Byte ' Get the hWnd of the target application
ThWnd = FindWindow(vbNullString, "Target")
a$ = "It Works!"
' Copy the string into a byte array, converting it to ASCII
Call CopyMemory(buf(1), ByVal a$, Len(a$))
cds.dwData = 3
cds.cbData = Len(a$) + 1
cds.lpData = VarPtr(buf(1))
i = SendMessage(ThWnd, WM_COPYDATA, Me.hwnd, cds)
End Sub Private Sub Form_Load()
' This gives you visibility that the target app is running
' and you are pointing to the correct hWnd
Me.Caption = Hex$(FindWindow(vbNullString, "Target"))
End SubSave the project.
[/ol]
Running the Sample:
[ol]Restore the target application and press the F5 key to run the project. Note that the value of the hWnd displayed in the label. Restore the sending application and press the F5 key to run the project. Verify that the hWnd in the form caption matches the hWnd in the label on the target application. Click the CommandButton and the text message should be displayed on the form of the target application. [/ol] |
|
置顶卡
