Error: Object reference not set to an instance of

[defi]

Hi!

i get this error when i try to compile my program using Visual Studio and Enterprise Architect.

I'm writing a tool for Enterprise Architect, and i have to make a graph, and i continue to get this error, i don't know what to do.

The code that i have problem with is:

public Graph(EA.Repository repository)
        {

            EA.Diagram maindiagram;
            this.modelRepository = repository;
            maindiagram = repository.GetCurrentDiagram(); //recupero del diagramma
            this.diagramId = maindiagram.DiagramID; //identificativo del diagramma

            //inizializzazione nodi
            Collection nodeCollection = maindiagram.DiagramObjects;
            nodeList = new ArrayList();
            

            foreach (DiagramObject diagram in maindiagram.DiagramObjects)
            {
                diagramList.Add(diagram);
                foreach (Element element in diagramList)
                {
                    if (element.Type == "Class"|| element.Type == "Component"||element.Type == "Package")
                    { nodeList.Add(new Node(diagram, ref repository)); }
                  
                }                
                
            }

            //inizializzazione archi
            Collection linkCollection = maindiagram.DiagramLinks;
            linkList = new ArrayList();

            foreach (DiagramLink edge in maindiagram.DiagramLinks)
            {
                edgeList.Add(edge);
                foreach(Connector connector in edgeList)
                    if (connector.Type == "Association" || connector.Type == "Aggregation" || connector.Type == "Compose" || connector.Type == "Dependency"
                        || connector.Type == "Generalization" || connector.Type == "Realization")
                    { linkList.Add(new Link (edge, ref repository));}
            }
Please help if you know how.

Thank you a lot!

[Geert Bellekens]

You could start by telling us which object is NULL

Geert

[defi]

uhh sorry,
well it shows me for:

• this.diagramId = maindiagram.DiagramID;
•   diagramList.Add(diagram);

[Geert Bellekens]

omg

Ok, hover your mouse over the...

pff, nevermind..

Geert

[defi]

why this kind of answer?
sorry if is a stupid question for you, but i'm trying to learn something, if you don't want to help, don't bother to answer, thank you a lot for your time.

[qwerty]

I'm no Cxx-hacker but what I see from your program is that you should re-start with some very basics.

q.

[KP]

You need to check the return value from GetCurrentDiagram() before using it.

[philchudley]

The diagramID will be null if there is no diagram open when your add-in runs.

Open a diagram, then run your add-in.

... also as KP suggested, test for null before using the returned value.


maindiagram = repository.GetCurrentDiagram(); //recupero del diagramma
if (mainDiagram != null) {
     this.diagramId = maindiagram.DiagramID; //identificativo del diagramma
}

[defi]

Ok thank you, i wrote and if condition before every value that accure that error and now i don't get any error, but eather an result. I'll keep working on it.

Thank you a lot for your help.