[Mono-bugs] [Bug 692444] New: GroupBy throws when accessing property for first time (MonoTouch 4.0.3)

[bugzilla_noreply at novell.com]

https://bugzilla.novell.com/show_bug.cgi?id=692444

https://bugzilla.novell.com/show_bug.cgi?id=692444#c0


           Summary: GroupBy throws  when accessing property for first time
                    (MonoTouch 4.0.3)
    Classification: Mono
           Product: MonoTouch
           Version: unspecified
          Platform: iPhone
        OS/Version: Other
            Status: NEW
          Severity: Major
          Priority: P5 - None
         Component: Runtime
        AssignedTo: mono-bugs at lists.ximian.com
        ReportedBy: krisow+novell at gmail.com
         QAContact: mono-bugs at lists.ximian.com
          Found By: Development
           Blocker: No


Description of Problem:
When I use GroupBy to group by a property that hasn't been accessed yet (even
though the property is set at startup), a NullReferenceException is thrown.

Steps to reproduce the problem:
I have an object with a DateTime property. When I try to group by
DateTime.Date, I get this exception. However, if I access the Date property
prior to GroupBy, I don't get the exception.

My GroupBy statement, which throws the exception:
foreach(var dateGroup in DataStore.Instance.ClassItems.GroupBy(c =>
c.StartTime.Date))

However, if I add a no-op statement that accesses StartTime.Date prior to the
GroupBy, no exception is thrown for the GroupBy:
foreach(var classItem in DataStore.Instance.ClassItems)
    if(classItem.StartTime.Date == DateTime.Now) ...

The DataStore is a singleton, and class items are currently mocked in the
constructor:
public class DataStore
{
    private static readonly DataStore instance = new DataStore();
    public static DataStore Instance
    {
        get { return instance; }
    }

    private DataStore()
    {
        this.ClassItems = new List<ClassItem>();
        // Generate mock ClassItems
    }
}

Actual Results:
System.NullReferenceException: Object reference not set to an instance of an
object
  at Mono.Debugging.Client.ObjectValue.GetChild (System.String name) [0x00000]
in <filename unknown>:0 
  at Mono.Debugging.Client.ExceptionStackFrame.get_File () [0x00000] in
<filename unknown>:0 
  at MonoDevelop.Debugger.ExceptionCaughtDialog.ShowStackTrace
(Mono.Debugging.Client.ExceptionInfo exc, Boolean showExceptionNode) [0x00000]
in <filename unknown>:0 
  at MonoDevelop.Debugger.ExceptionCaughtDialog.Fill () [0x00000] in <filename
unknown>:0 
  at MonoDevelop.Debugger.ExceptionCaughtDialog.<HandleExceptionChanged>m__0
(System.Object , System.EventArgs ) [0x00000] in <filename unknown>:0 
  at Gtk.Application+InvokeCB.Invoke () [0x00000] in <filename unknown>:0 
  at GLib.Timeout+TimeoutProxy.Handler () [0x00000] in <filename unknown>:0 

Expected Results:
No exception when property is non-null.

How often does this happen? 
Always.

Additional Information:

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