| Visual Basic 6.0 applications can access Win32 API. Win32 API consists of the various functions and types that can be accessed by the Visual Basic applications. Visual Studio comes with the API text viewer utility. This utility can be used by application developers to find out the various functions and types that need to be used in Visual Basic 6.0 applications. Win32 functions provide functions for Windows management, system services, GDI- related functions such as BitBlt , and multimedia-related functionalities. When the Visual Basic 6.0 applications containing Win32 API calls are upgraded to Visual Basic .NET, the code gets upgraded with a runtime warning. Because parameters passed to the function may contain user -defined types, the upgrade wizard converts such types into structures. These types could contain fixed-length strings in Visual Basic 6.0. However, they are no longer supported in Visual Basic .NET. As a result, some modifications have to be done to the Visual Basic .NET code. CODE EXAMPLES Example 18 In the following code example, the Visual Basic 6.0 application uses the Win32 API call to the GetSystemInfo function. This application finds three things, the processor type, the number of processors, and the page size , and displays the results in a RichTextBox control. The following code is in the SystemInfo-VB folder for this chapter:  Private Sub Command1_Click() Dim objSystemInfo As SYSTEM_INFO Call GetSystemInfo(objSystemInfo) RichTextBox1.Text = "" RichTextBox1.Text = RichTextBox1.Text & _ "Processor Type = " & vbTab & vbTab & _ objSystemInfo.dwProcessorType & vbCrLf RichTextBox1.Text = RichTextBox1.Text & _ "Page Size = " & vbTab & vbTab & _ objSystemInfo.dwPageSize & vbCrLf RichTextBox1.Text = RichTextBox1.Text & _ "Number of Processors = " & vbTab & _ objSystemInfo.dwNumberOrfProcessors Command2.SetFocus End Sub The following module is in the same folder. This module contains a Win32 API function declaration. Public Type SYSTEM_INFO dwOemID As Long dwPageSize As Long lpMinimumApplicationAddress As Long lpMaximumApplicationAddress As Long dwActiveProcessorMask As Long dwNumberOrfProcessors As Long dwProcessorType As Long dwAllocationGranularity As Long dwReserved As Long End Type Public Declare Sub GetSystemInfo Lib "kernel32" _ (lpSystemInfo As SYSTEM_INFO) Public Declare Function GetLastError Lib "kernel32" () _ As Long When this Visual Basic 6.0 code is upgraded, the Visual Basic form's code gets converted into Windows Forms code. The user-defined type gets changed to a structure. Also the upgrade wizard introduces a runtime warning. The following equivalent Visual Basic .NET code is in the SystemInfo-VB.NET folder for this chapter: Private Sub Command1_Click(ByVal eventSender As _ System.Object, ByVal eventArgs As System.EventArgs) _ Handles Command1.Click Dim objSystemInfo As SYSTEM_INFO Call GetSystemInfo(objSystemInfo) RichTextBox1.Text = "" RichTextBox1.Text = RichTextBox1.Text & _ "Processor Type = " & vbTab & vbTab & _ objSystemInfo.dwProcessorType & vbCrLf RichTextBox1.Text = RichTextBox1.Text & _ "Page Size = " & vbTab & vbTab & _ objSystemInfo.dwPageSize & vbCrLf RichTextBox1.Text = RichTextBox1.Text & _ "Number of Processors = " & vbTab & _ objSystemInfo.dwNumberOrfProcessors Command2.Focus() End Sub Private Sub Command2_Click(ByVal eventSender As _ System.Object, ByVal eventArgs As System.EventArgs) _ Handles Command2.Click End End Sub The following module declaration has been kept in the same directory. Module Module1 Public Structure SYSTEM_INFO Dim dwOemID As Integer Dim dwPageSize As Integer Dim lpMinimumApplicationAddress As Integer Dim lpMaximumApplicationAddress As Integer Dim dwActiveProcessorMask As Integer Dim dwNumberOrfProcessors As Integer Dim dwProcessorType As Integer Dim dwAllocationGranularity As Integer Dim dwReserved As Integer End Structure 'UPGRADE_WARNING: Structure SYSTEM_INFO may require marshal- ling attributes to be passed as an argument in this 'Declare statement. Click for more: 'ms-'help://MS.VSCC/commoner/redir/ redirect.htm?keyword="vbup10'50"' Public Declare Sub GetSystemInfo Lib "kernel32" _ (ByRef lpSystemInfo As SYSTEM_INFO) Public Declare Function GetLastError Lib "kernel32" _ ()As Integer End Module As shown in this code for the module, a runtime warning is issued. The warning states that if the type contained in Visual Basic includes fixed-length strings, marshalling attributes have to be used to make the code work in Visual Basic .NET. For this example, because the fixed-length strings are not used, no marshalling attributes are required and the code delivers the same functionality in Visual Basic .NET without requiring any code changes to be made by the developer. | 
