nullreferenceexception

I've been using the same bit of code for several versions of my app with no problems, but I'm now mysteriously receiving NullRerefenceException s with the following: this.Loaded += delegate { deleteBrush = new DeleteBrushAdorner( background ); AdornerLayer al = AdornerLayer.GetAdornerLayer( background ); al.Add( deleteBrush ); // null ref here?? }; background is just a Border element. My two thoughts on what could be causing it are a) switching to .NET 4.0, and b) placing instances of the above element (which is a UserControl ) in an ItemsControl . Oddly this doesn't happen all the time, and

This is a weird one, and I'm at a loss to understand what's going on here. I have a web api project that in one controller a call to a certain method eventually calls a function in a service that looks like this: public MyClassBase GetThing(Guid id) { if (cache.ContainsKey(id)) { return cache[id]; } else { var type = typeof(MyClassBase).Assembly.GetTypes().FirstOrDefault ( t => t.IsClass && t.Namespace == typeof(MyClassBase).Namespace + ".Foo" && t.IsSubclassOf(typeof(MyClassBase)) && (t.GetCustomAttribute<MyIdAttribute>()).GUID == id ); if (type != null) { System.Diagnostics.Debug.WriteLine

Looking for some best-practice guidance. Let's say I have a line of code like this: Color color = someOrder.Customer.LastOrder.Product.Color; where Customer, LastOrder, Product, and Color could be null under normal conditions. I'd like color to be null if any one of the objects in the path is null, however; in order to avoid null reference exceptions, I'd need to check for the null condition for each one of the objects, e.g. Color color = someOrder == null || someOrder.Customer == null || someOrder.Customer.LastOrder == null || someOrder.Customer.Product == null ? null : someOrder.Customer

I'm pretty new in the ASP .NET MVC world. Maybe, that's the reason I can't explain to myself the cause of what is, for me, an annoying problem. I have one class with One-To-Many relashionship. class MyClass{ public List<OtherClass> otherClasses {get;set;} } When I'm persisting one instance of this class, I fill it's relationship with an empty List<> MyClass myClass = new MyClass(){ otherClasses = new List<OtherClass>() } context.myClass.Add(myClass); The problem is that, when I try to retrieve that instance, and for any reason, I try to access that list, system gives me a Null Reference

This question already has an answer here: What is a NullReferenceException, and how do I fix it? 31 answers In my asp.net program.I set one protected list.And i add a value in list.But it shows Object reference not set to an instance of an object error protected List<string> list; protected void Page_Load(object sender, EventArgs e) { list.Add("hai"); } How to solve this error? You need to initialize the list first: protected List<string> list = new List<string>(); I think you just need; List<string> list = new List<string>(); list.Add("hai"); There is a difference between List<string> list;

So here's an excerpt from one of my classes: [ThreadStatic] readonly static private AccountManager _instance = new AccountManager(); private AccountManager() { } static public AccountManager Instance { get { return _instance; } } As you can see, it's a singleton-per-thread - i.e. the instance is marked with the ThreadStatic attribute. The instance is also instantiated as part of static construction. So that being the case, how is it possible that I'm getting a NullReferenceException in my ASP.NET MVC application when I try to use the Instance property? Quoting MSDN ThreadStaticAttribute : Do