error... object reference not set to an instance of an object

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Hi guy's I'have this problem driving me crazy i'trayed to build vb.net application.... extract zip file from resource but i'get this error (object reference not set to an instance of an object)
this is the code

VB

Dim sc As New Shell32.Shell()
        'Create directory in which you will unzip your files .
        IO.Directory.CreateDirectory("D:\Test")
        'Declare the folder where the files will be extracted
        Dim output As Shell32.Folder = sc.NameSpace("D:\Test")
        'Declare your input zip file as folder  .
        Dim input As Shell32.Folder = sc.NameSpace(My.Resources.zipfile)
        'Extract the files from the zip file using the CopyHere command .
        output.CopyHere(input.Items, 4)
        Me.Close()

please help guy's

Posted 1-Mar-15 4:58am

Member 11392696

Updated 1-Mar-15 5:06am

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Sergey Alexandrovich Kryukov 1-Mar-15 22:03pm

In what line?
—SA

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OriginalGriff · Answer 1 · 2015-03-01T05:59:00

Use the debugger: put a breakpoint on the first line of that code, and single step through. At each stage, before you execute a line hover the mouse over the variables, and look for null (or Nothing) values.

When you find one (like output for example) that is null and about to be used (as output is in the second to last line) then you can start to work out why it's null.

We can't do it for you: my HDD is not organised in the same way, so your code may not even give an error for me. It's quite likely that the NameSpace call is the problem: if the folder doesn't exist, it may return null - but I can't find out for you!

Sergey Alexandrovich Kryukov · Answer 2 · 2015-03-01T16:03:00

You did not show where the exception with the message "Object reference not set to an instance of an object" is thrown.

Not to worry. 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"[^].

Sometimes, you cannot do it under debugger, by one or another reason. One really nasty case is when the problem is only manifested if software is built when debug information is not available. In this case, you have to use the harder way. First, you need to make sure that you never block propagation of exceptions by handling them silently (this is a crime of developers against themselves, yet very usual). The you need to catch absolutely all exceptions on the very top stack frame of each thread. You can do it if you handle the exceptions of the type System.Exception. In the handler, you need to log all the exception information, especially the System.Exception.StackTrace:
http://msdn.microsoft.com/en-us/library/system.exception.aspx[^],
http://msdn.microsoft.com/en-us/library/system.exception.stacktrace.aspx[^].

The stack trace is just a string showing the full path of exception propagation from the throw statement to the handler. By reading it, you can always find ends. For logging, it's the best (in most cases) to use the class System.Diagnostics.EventLog:
http://msdn.microsoft.com/en-us/library/system.diagnostics.eventlog.aspx[^].

Good luck,

—SA

error... object reference not set to an instance of an object

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