[RESOLVED] Exception Problems.

Hi all,
I'm Creating a wrapper dll for my favorite Windows API functions. Normally when windows API calls fail, Nothing happens and you don't know why and this frustrates me. Although you can use their return value to determine If it was successful.

My code (one example)

vb.net Code:

Public Function SetParent(ByVal hWndChild As IntPtr, ByVal hWndNewParent As IntPtr) As IntPtr
        Dim result As IntPtr = Declarations.SetParent(hWndChild, hWndNewParent)
        If result = IntPtr.Zero Then
 
            Dim ex As New System.ComponentModel.Win32Exception(Runtime.InteropServices.Marshal.GetLastWin32Error)
           throw ex
 
 
 
        End If
    End Function

My problem is that when I create a new exception to be thrown I can't set the stack trace or other necessary information. I need to set this because when I just throw the exception the debugger will go to the line that threw the exception and Not the actual call.

Any ideas ?

EDIT: It seems like the only way is to create a custom exception. I don't want to do that since I like the Win32 exception.

Add a

Code:

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<DebuggerStepThrough()> _

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attribute on the line before your function.

That is quite cool :) Thanks !

Quote:

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Originally Posted by BlindSniper

Hi all,
Normally when windows API calls fail, Nothing happens and you don't know why and this frustrates me. Although you can use their return value to determine If it was successful.

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For a fully trusted application you can get both an error code and description for a failure of an API call shown below.

Code:

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Imports System.Runtime.InteropServices
Imports System.ComponentModel
Public Class Form1
    Private Sub cmdTest_Click() Handles cmdTest.Click
        Console.WriteLine("Calling Win32 MessageBox without error...")
        Win32.MessageBox(New IntPtr(0), "Press OK...", "Press OK Dialog", 0)

        Dim ErrorCode As Integer = Marshal.GetLastWin32Error()
        If ErrorCode = 0 Then
            Console.WriteLine("1. Worked just fine")
        Else
            Dim ErrorMsg As New Win32Exception(ErrorCode)
            Console.WriteLine("1. The last Win32 Error was: {0} Description [{1}]", _
                              ErrorCode, ErrorMsg.Message)
        End If

        ' Call the MessageBox with an invalid window handle to produce a Win32 error.
        Win32.MessageBox(New IntPtr(123132), "Press OK...", "Press OK Dialog", 0)
        ErrorCode = Marshal.GetLastWin32Error()
        If ErrorCode = 0 Then
            Console.WriteLine("2. Worked just fine")
        Else
            Dim ErrorMsg As New Win32Exception(ErrorCode)
            Console.WriteLine("2. The last Win32 Error was: {0} Description [{1}]", _
                              ErrorCode, ErrorMsg.Message)
        End If
    End Sub
End Class

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Code:

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Imports System.Runtime.InteropServices
Module Win32
    ' Use DllImportAttribute to inport the Win32 MessageBox
    ' function.  Set the SetLastError flag to true to allow
    ' the function to set the Win32 error.
    <DllImportAttribute("user32.dll", _
                        SetLastError:=True, _
                        CharSet:=CharSet.Unicode)> _
    Function MessageBox( _
        ByVal hwnd As IntPtr, _
        ByVal text As String, _
        ByVal caption As String, _
        ByVal type As UInt32) As Integer
    End Function
    <DllImport("Kernel32.dll", _
              EntryPoint:="FormatMessageW", _
              SetLastError:=True, _
              CharSet:=CharSet.Unicode, _
              CallingConvention:=CallingConvention.StdCall)> _
    Public Function FormatMessage( _
        ByVal dwFlags As Integer, _
        ByRef lpSource As IntPtr, _
        ByVal dwMessageId As Integer, _
        ByVal dwLanguageId As Integer, _
        ByRef lpBuffer As String, _
        ByVal nSize As Integer, _
        ByRef Arguments As IntPtr) As Integer
    End Function
End Module

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Output

Code:

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Calling Win32 MessageBox without error...
1. Worked just fine
2. The last Win32 Error was: 1400 Description [Invalid window handle]

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Since it fits here any ways, same as kevin, a few functions to shorten it all. Import interopservices btw.

Code:

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    Public Shared Function HasError() As Boolean
        Return Marshal.GetLastWin32Error() <> 0
    End Function
    Public Shared Function LastError() As Exception
        Return New System.ComponentModel.Win32Exception(Marshal.GetLastWin32Error())
    End Function
    <DebuggerStepThrough()> _
    Public Shared Sub HandleError()
        If HasError() Then Throw LastError
    End Sub

    Public Sub ThrowError(Optional ByVal location As String = "")
        Dim ex As New System.ComponentModel.Win32Exception(Runtime.InteropServices.Marshal.GetLastWin32Error())
        If ex.NativeErrorCode <> 0 Then MessageBox.Show(ex.Message, "Error at " & location, MessageBoxButtons.OK, MessageBoxIcon.Error)
    End Sub

    Public Function GetLastError() As String
        Return New System.ComponentModel.Win32Exception(Runtime.InteropServices.Marshal.GetLastWin32Error()).Message
    End Function

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Code:

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'Error in an API right here
ThrowError("Sending a message to my form.")
MsgBox(GetLastError())
HandleError()
If HasError Then Throw LastError()

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Quote:

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Originally Posted by bergerkiller

Since it fits here any ways, same as kevin, a few functions to shorten it all. Import interopservices btw.

Code:

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    Public Shared Function HasError() As Boolean
        Return Marshal.GetLastWin32Error() <> 0
    End Function
    Public Shared Function LastError() As Exception
        Get
            Return New System.ComponentModel.Win32Exception(Marshal.GetLastWin32Error())
            End If
        End Get
    End Function

    Public Sub ThrowError(Optional ByVal location As String = "")
        Dim ex As New System.ComponentModel.Win32Exception(Runtime.InteropServices.Marshal.GetLastWin32Error())
        If ex.NativeErrorCode <> 0 Then MessageBox.Show(ex.Message, "Error at " & location, MessageBoxButtons.OK, MessageBoxIcon.Error)
    End Sub

    Public Function GetLastError() As String
        Return New System.ComponentModel.Win32Exception(Runtime.InteropServices.Marshal.GetLastWin32Error()).Message
    End Function

---

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I've corrected the errors in your syntax:

Code:

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    Public Shared Function HasError() As Boolean
        Return Marshal.GetLastWin32Error() <> 0
    End Function

    Public Shared ReadOnly Property LastError() As ComponentModel.Win32Exception
        Get
            Return New ComponentModel.Win32Exception(Marshal.GetLastWin32Error())
        End Get
    End Function

    Public Sub ThrowError(Optional ByVal location As String = "")
        Dim ex As ComponentModel.Win32Exception = LastError
        If ex.NativeErrorCode <> 0 Then MessageBox.Show(ex.Message, "Error at " & location, MessageBoxButtons.OK, MessageBoxIcon.Error)
    End Sub

    Public Function GetLastError() As String
        Return LastError.Message
    End Function

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EDIT: I see you edited your post.

Yep sorry, noticed the leftovers from the property->function change just as you did. :D
Ow and the last two functions came from a separate class, thus the duplicate exception creation code.

Made it all even shorter, all you have to do is call "HandleError" and it will bring you to where it is called if there is an error, and display the exception in the debugger:

Code:

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    'Error handling
    Private Shared LastError As Exception
    <DebuggerStepThrough()> _
    Public Shared Sub HandleError()
        If LastError IsNot Nothing Then
            Throw LastError
        ElseIf Marshal.GetLastWin32Error() <> 0 Then
            Throw New System.ComponentModel.Win32Exception(Marshal.GetLastWin32Error())
        End If
    End Sub

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The LastError member allows you to specify a custom error in case the LastWin32Error is not set.