Q241530: HOWTO: Call an API That Uses Structures from eVB/VBCE6
Article: Q241530
Product(s): Microsoft Visual Basic for Windows
Version(s): 1.0,3.0
Operating System(s):
Keyword(s): kbAPI kbToolkit kbVBp600 kbOSWinCEsearch kbGrpDSVB kbUserDT
Last Modified: 13-MAY-2002
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The information in this article applies to:
- Microsoft Windows CE Toolkit for Visual Basic 6.0, version 1.0
- Microsoft eMbedded Visual Basic, version 3.0
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SUMMARY
=======
"Currently there is no explicit support for user-defined data types (UDTs) in
either eMbedded Visual Basic 3.0 (eVB) or the Microsoft Windows CE Toolkit for
Visual Basic 6.0 (VBCE).
This article illustrates one approach to calling Windows CE APIs from eVB/VBCE
applications that require the use of UDT structures. This method requires use of
advanced manipulation techniques for storing this data in memory.
MORE INFORMATION
================
Microsoft provides programming examples for illustration only, without warranty
either expressed or implied, including, but not limited to, the implied
warranties of merchantability and/or fitness for a particular purpose. This
article assumes that you are familiar with the programming language being
demonstrated and the tools used to create and debug procedures. Microsoft
support professionals can help explain the functionality of a particular
procedure, but they will not modify these examples to provide added
functionality or construct procedures to meet your specific needs. If you have
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WARNING: This article assumes advanced knowledge of user-defined data types and
their use with Win32 API calls in Microsoft Visual Basic. This method is not
supported by Microsoft.
A UDT is a data structure that can store multiple related variables of different
types. UDTs are very useful when you want to pass several related pieces of
information in one parameter of a function call. Unfortunately, because UDTs are
not directly supported in either eVB or VBCE, this limits you to which API calls
you can use from your eVB/VBCE programs.
As a workaround to this limitation, there is a way you can manipulate the data
and coax the contents of your would-be UDTs into a String variable that can be
passed into an API call in the same format as a UDT would pass them. This
example shows how to convert Long Integer data types into a string format
compatible with how data is stored in memory.
NOTE: Be careful with the Declaration statement in eVB/VBCE. The UDT should
always be specified as a String passed ByVal. This is in contrast to what you
find in the "API Text Viewer" viewing the Winceapi.txt file.
1. Create a new Windows CE project in either Visual Basic or eMbedded Visual
Basic. Form1 is created by default.
2. On the Project menu, select Add Module to add a module. Module1 is created by
default.
3. Paste the the following code into Module1:
Option Explicit
'
' Note: lpRect is passed as ByVal.
Declare Function GetWindowRect Lib "Coredll" ( _
ByVal hwnd As Long, ByVal lpRect As String) As Long
Public Function MemStringToLong(StringIn As String) As Long
On Error Resume Next
Dim hWorkVal As String
'
' Convert the String back to Long Integer.
' Converting back to Big Endian format.
hWorkVal = Hex(AscB(MidB(StringIn, 2, 1)))
If Not Err Then
hWorkVal = hWorkVal & Hex(AscB(MidB(StringIn, 1, 1)))
End If
'
' Return Long Integer value.
MemStringToLong = CLng("&H" & hWorkVal)
End Function
Public Sub getRECT(ByVal sRect As String, _
ByRef rLeft As Long, ByRef rTop As Long, _
ByRef rRight As Long, ByRef rBottom As Long)
'
' Convert memory-formatted String back to Long Integer.
rLeft = MemStringToLong(MidB(sRect, 1, 4))
rTop = MemStringToLong(MidB(sRect, 5, 4))
rRight = MemStringToLong(MidB(sRect, 9, 4))
rBottom = MemStringToLong(MidB(sRect, 13, 4))
End Sub
Public Function LongToMemoryString(ByVal lInputValue As Long) As String
Dim hWorkVal As String
'
' Convert to HEX value.
hWorkVal = Hex(lInputValue)
'
' Check to see if it is not zero.
If hWorkVal <> "0" Then
'
' Convert to memory storage format (Little Endian).
' For example, 0000A411 would convert to 11A40000.
' Use ChrB to rebuild Bytes.
LongToMemoryString = ChrB(CInt("&H" & Mid(hWorkVal, 3, 2)))
LongToMemoryString = LongToMemoryString & _
ChrB(CInt("&H" & Mid(hWorkVal, 1, 2)))
LongToMemoryString = LongToMemoryString & ChrB(CInt("&H00"))
LongToMemoryString = LongToMemoryString & ChrB(CInt("&H00"))
Else
' Just return zeros.
' Use ChrB to build Bytes.
LongToMemoryString = ChrB(CInt("&H00"))
LongToMemoryString = LongToMemoryString & ChrB(CInt("&H00"))
LongToMemoryString = LongToMemoryString & ChrB(CInt("&H00"))
LongToMemoryString = LongToMemoryString & ChrB(CInt("&H00"))
End If
End Function
Public Function RECT(rLeft As Long, rTop As Long, _
rRight As Long, rBottom As Long) As String
'
' Convert inbound Long Integers to a memory storage String format.
RECT = LongToMemoryString(rLeft) & _
LongToMemoryString(rTop) & _
LongToMemoryString(rRight) & _
LongToMemoryString(rBottom)
End Function
4. Add a Command button to Form1.
5. Paste the following code into Form1:
Option Explicit
Private Sub Form_Load()
Command1.Move 120, 120, 2000, 600
Command1.Caption = "Get Form1 RECT Info."
End Sub
Private Sub Command1_Click()
Dim lRet As Long
Dim sMessage As String
Dim sRect As String
Dim rLeft As Long
Dim rTop As Long
Dim rRight As Long
Dim rBottom As Long
'
' Initialize RECT memory string.
' Convert initial Rect values to String to pass into GetWindowRect API.
sRect = RECT(rLeft, rTop, rRight, rBottom)
'
' Call GetWindowRect.
lRet = GetWindowRect(Me.hwnd, sRect)
'
' Test return value.
If lRet > 0 Then
'
' Convert String back to Long Integer.
getRECT sRect, rLeft, rTop, rRight, rBottom
'
' Display results.
sMessage = "RECT is defined as follows:" & vbCrLf
sMessage = sMessage & "Left: " & rLeft & vbCrLf
sMessage = sMessage & "Top: " & rTop & vbCrLf
sMessage = sMessage & "Right: " & rRight & vbCrLf
sMessage = sMessage & "Bottom: " & rBottom
MsgBox sMessage, vbOKOnly + vbInformation, "Form Settings"
Else
MsgBox "Call to GetWindowRect Failed.", _
vbOKOnly + vbCritical, "Failure"
End If
End Sub
6. Run the application.
7. Click on the Command button and note the results.
REFERENCES
==========
For additional information, click the article number below to view the article
in the Microsoft Knowledge Base:
Q102025 Explanation of Big Endian and Little Endian Architecture
For more information, please see the MSDN:
Creating User-Defined Types for DLL Functions
Creating Your Own Data Types
Additional query words: vbce6 vcce6 wce eVB
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Keywords : kbAPI kbToolkit kbVBp600 kbOSWinCEsearch kbGrpDSVB kbUserDT
Technology : kbVBSearch kbAudDeveloper kbZNotKeyword2 kbVBeMbSearch kbWinCETKVBSearch kbWinCESearch kbWinCETK100VB600 kbVBeMb300
Version : :1.0,3.0
Hardware : WinCE
Issue type : kbhowto
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