Object reference not set to an instance of an object

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Hi
I have a ImageList from my UserControl in visual c++ 2012 cli in .net 4 and I added some images in my ImageList to the set buttons images, but when I run my project I get this error in the header file can any one tell me what is problem ?

An unhandled exception of type 'System.NullReferenceException' occurred in
Additional information: Object reference not set to an instance of an object.

my image list from header file initialize with this commands

C++

System::ComponentModel::ComponentResourceManager^  resources = (gcnew System::ComponentModel::ComponentResourceManager(SignalDisplayControl::typeid));
this->imageList1->ImageStream = (cli::safe_cast<System::Windows::Forms::ImageListStreamer^  >(resources->GetObject(L"imageList1.ImageStream")));
					this->imageList1->TransparentColor = System::Drawing::Color::Transparent;
					this->imageList1->Images->SetKeyName(0, L"Alarm_Acked.png");

Thank you guys ;-)

Posted 15-Dec-13 7:35am

Aydin Homay

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CHill60 15-Dec-13 13:44pm

Is the line that throws the exception included in this code snippet?

Sergey Alexandrovich Kryukov 15-Dec-13 14:15pm

In what line? Did you use the debugger?
—SA

Aydin Homay 15-Dec-13 14:21pm

I get this exception in this line :
this->imageList1->ImageStream = (cli::safe_cast<system::windows::forms::imageliststreamer^>(resources->GetObject(L"imageList1.ImageStream")));

Sergey Alexandrovich Kryukov 15-Dec-13 15:08pm

Probably GetObject returns null. In my answers, I explained what you should do. Please follow my instructions.
—SA

Member 11043556 28-Aug-14 14:02pm

Thank you Sergey, ill give your Answer a shot! :D

2 solutions

Solution 2

dont do anything just learn try catch block and see what happen in it?

Posted 16-Dec-13 1:27am

Gaurav Makwana

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Sergey Alexandrovich Kryukov · Accepted Answer · 2013-12-15T08:17:00

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