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How do you trap a 'System.NullReferenceException' in

P: n/a
This code seems to "work" but I get the following errors:

An unhandled exception of type 'System.NullReferenceException' occurred in
then this one:
An unhandled exception of type 'System.ExecutionEngineException' occurred in

Anyone know how to either trap these errors or prevent them from happening?


Public Class Form1

Inherits System.Windows.Forms.Form

#Region " Windows Form Designer generated code "

Public Sub New()


'This call is required by the Windows Form Designer.


'Add any initialization after the InitializeComponent() call

End Sub

'Form overrides dispose to clean up the component list.

Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)

If disposing Then

If Not (components Is Nothing) Then


End If

End If


End Sub

'Required by the Windows Form Designer

Private components As System.ComponentModel.IContainer

'NOTE: The following procedure is required by the Windows Form Designer

'It can be modified using the Windows Form Designer.

'Do not modify it using the code editor.

Friend WithEvents Button1 As System.Windows.Forms.Button

<System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()

Me.Button1 = New System.Windows.Forms.Button





Me.Button1.Location = New System.Drawing.Point(48, 80)

Me.Button1.Name = "Button1"

Me.Button1.Size = New System.Drawing.Size(176, 40)

Me.Button1.TabIndex = 0

Me.Button1.Text = "Button1"




Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)

Me.ClientSize = New System.Drawing.Size(292, 266)


Me.Name = "Form1"

Me.Text = "Form1"


End Sub

#End Region

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button1.Click

GetClientRect(GetDesktopWindow, rct)

InvertRect(GetWindowDC(GetDesktopWindow), rct)

End Sub

'Original Example by BD (ou***;

Private Declare Function InvertRect Lib "user32" (ByVal hdc As Long, ByVal
lpRect As Rect) As Long

Private Declare Function GetWindowDC Lib "user32" (ByVal hwnd As Long) As

Private Declare Function GetClientRect Lib "user32" (ByVal hwnd As Long,
ByVal lpRect As Rect) As Long

Private Declare Function GetDesktopWindow Lib "user32" () As Long

Private Structure Rect

Dim Left As Long

Dim Top As Long

Dim Right As Long

Dim Bottom As Long

End Structure

Private rct As Rect

End Class

Jul 21 '05 #1
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1 Reply

P: n/a
Hello Greg,

Thanks for your post. As I understand the problem you are facing is that it
throws NullReferenceException from your WinForm application. I'd like to
share the following information with you:

Generally speaking, NullReferenceException is thrown when there is an
attempt to dereference a null object reference. For example, when we use a
class without instantiating (New) the class. To trap the errors, I
recommend that you can use structured error handling (Try...Catch...Finally
statement) and examine the exception's call stack which may tell us the
root cause of the problem. Please refer to the followign KB article for
detailed information on structured error handling:

INFO: Error Handling in Visual Basic .NET

I look forwrad to your feedback.


Microsoft Online Partner Support

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Jul 21 '05 #2

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