ObservableCollection.Add() calls a NullReferenceException

Question

I have a strange dilemma that is making no sense. When I call properties.Add after a button click, the debugger shows a NullReferenceException .

The error is shown in the following constructor for MainWindow():

class GlobalProperties
{
    public ObservableCollection<Property> Properties { get; set; }
    public ObservableCollection<Photo> Photos { get; set; }
    public ObservableCollection<Problem> Issues { get; set; }
    public ObservableCollection<Tennant> Tennants { get; set; }
}

public partial class MainWindow : Window
{
    //...
    GlobalProperties globalProperties = new GlobalProperties();

    public MainWindow(User curUser)
    {
        ObservableCollection<Property> properties = globalProperties.Properties;
        properties.Add(new Property("58 Huet St", "Nundah", "4012", 4000.00, new LinkedList<Tennant>(), 5, 4, 2, 0, "Beautiful house. In Nundah. It's pretty cool. And you should live there. This is an optional piece of text.", new LinkedList<Photo>(), "Home", 48.23, 86.74, "Humid", new LinkedList<Problem>(), "Townhouse", 2004, 1800)); // This line has the problem
        globalProperties.Properties = properties;
        InitializeComponent();
        this.DataContext = this;
    }

Why am I getting this NullReferenceException ? It was working perfectly before I set up some Binding things on the MainWindow, after which it started giving me this.

Edit: Found the StackTrace:

at VentureVisions.view.MainWindow..ctor(User curUser) in c:\Source\Stuff\CS IA\VentureVisions\VentureVisions\view\MainWindow.xaml.cs:line 36
at VentureVisions.view.Login.OnClosing(CancelEventArgs e) in c:\Source\Stuff\CS IA\VentureVisions\VentureVisions\view\Login.xaml.cs:line 42
at System.Windows.Window.WmClose()
at System.Windows.Window.WindowFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at System.Windows.Interop.HwndSource.PublicHooksFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)
at System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs)
at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)

Answer 1

Based on the stack trace you posted, NullReferenceException is thrown in the constructor of MainWindow , in line 36 of MainWindow.xaml.cs to be exact.

Try checking that and if you're still stuck, post the code of that constructor as well, marking the problematic source code line.

EDIT:

Try adding the following constructor to GlobalProperties and check if that fixes the problem:

public GlobalProperties()
{
    Properties = new ObservableCollection<Property>();
    Photos = new ObservableCollection<Photo>();
    Issues = new ObservableCollection<Problem> ();
    Tennants = new ObservableCollection<Tennant>();
}

Answer 2

Try this

var window = new MainWindow();
Application.Current.MainWindow = window;
window.Show();
this.Close();