NullReferenceExecption when using StringCollection

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VS2012

Hello!

I am attempting to debug a small internet browser project, but attempting to list favourites from a StringCollection results in a NullReferenceException. Here is my code:

VB

Private Sub ToolStripDropDownButton1_Click(sender As Object, e As EventArgs) Handles ToolStripDropDownButton1.Click
    bookmarks = My.Settings.favourites
    For i = 0 To bookmarks.Count
        Dim ii As Int32 = i
        Dim fav As ToolStripMenuItem <--- Where I get the exception
        fav.ToolTipText = bookmarks.Item(ii)
        ToolStripDropDownButton1.DropDownItems.Add(fav)
    Next
End Sub

Any help would be appreciated.

Thanks!

-Orange

Posted 19-Mar-13 7:59am

OrangeFlash81

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2 solutions

Solution 2

Change

VB

Dim fav As ToolStripMenuItem

to

VB

Dim fav As New ToolStripMenuItem()

Basically you are trying to use an item you have not initialised.

Posted 19-Mar-13 8:08am

Pheonyx

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This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Sergey Alexandrovich Kryukov · Accepted Answer · 2013-03-19T08:07:00

Two bugs are obvious:

Instead of

VB

For i = 0 To bookmarks.Count

should be

VB

For i = 0 To bookmarks.Count - 1

And fav is not initialized. (This is VB.NET defect; in C# it would not compile.)

This is one of the very easiest cases to detect and fix. It simply means that some member/variable of some reference type is dereferenced by using and of its instance (non-static) members, which requires this member/variable to be non-null, but in fact it appears to be null. Simply execute it under debugger, it will stop the execution where the exception is thrown. Put a break point on that line, restart the application and come to this point again. Evaluate all references involved in next line and see which one is null while it needs to be not null. After you figure this out, fix the code: either make sure the member/variable is properly initialized to a non-null reference, or check it for null and, in case of null, do something else.

Please see also: want to display next record on button click. but got an error in if condition of next record function "object reference not set to an instance of an object"[^].

Good luck,

—SA

NullReferenceExecption when using StringCollection

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NullReferenceExecption when using StringCollection

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