System.StackOverflowException That makes no sense... how to debug?

Question

I'm building a WPF application that uses simple MVVM architecture and EF.

I'm seeing a weird issue where if I try to set a datetime property, I get a System.StackOverflowException. If I don't set the datetime property, I don't get the exception.

Binding:

   <DatePicker Style="{StaticResource Dp}" 
               Grid.Column="1" 
               SelectedDate="{Binding Date, UpdateSourceTrigger=PropertyChanged}" />

Public property:

public DateTime Date
{
    get
    {
        return _criticalDate.Date;
    }
    set
    {
        if (_criticalDate != null && value != null && _criticalDate.Date == value)
            return;
        _criticalDate.Date = value;
        OnPropertyChanged("Date");
    }
}

Trying to step through it with a debugger doesn't seem to work. I've looked at everything trying to see what is going on... any hints on what might be causing this?

This is the definition for the CriticalDate class,

public partial class CriticalDate
{
    public int ID { get; set; }
    public System.DateTime Date { get; set; }
    public string CriticalReason { get; set; }
    public int FileID { get; set; }
}

The _criticalDate field is a private instance of the CriticalDate class. CriticalDate is a class created by EF from my DB schema. It isn't itself a DateTime.

FINAL UPDATE

I still don't know what was wrong... I tore the offending section out (including the binding) and rewrote it from scratch. No clue what I did differently, but it works now. I think it was something to do with how an itemscontrol was set up... if I had more time (stupid deadlines) I'd go back to see what it was, but for now it's a mystery.

Thanks for sharing in my confusion, if only ever so briefly.

Answer 1

Try removing the OnPropertyChanged("Date");, or change the binding mode to OneWayToSource.

From the documentation of UpdateSourceTrigger.

Bindings that are TwoWay or OneWayToSource listen for changes in the target property and propagate them back to the source. This is known as updating the source. Usually, these updates happen whenever the target property changes. This is fine for check boxes and other simple controls, but it is usually not appropriate for text fields. Updating after every keystroke can diminish performance and it denies the user the usual opportunity to backspace and fix typing errors before committing to the new value. Therefore, the default UpdateSourceTrigger value of the Text property is LostFocus and not PropertyChanged.

I believe that OnPropertyChanged("Date"); on the Date_set method is updating the UI, which is in turn calling the Date_set method again, which completes the cycle and causes the recursion.

Answer 2

Edit: The following is useless since the debugger doesn't display a call stack for stack overflows. Instead, take a look at How to debug a stackoverflowexception in .NET

---

Set the Visual Studio debugger to break on StackOverflowExceptions and examine the callstack.

Ctrl+Alt+E

or

Debug->Exceptions...

Click Find and type StackOverflow then check the box in the Thrown column.

You will probably have hundreds of recursive calls in the same method or set of methods.

If the exception occurs inside a library, you might need to disable "Just My Code"

Answer 3

Make sure you are not updating your date when you don't need to, and break the feed back loop in your binding. I typically put this check around my setters:

public DateTime Date
{
    get
    {
        return _criticalDate.Date;
    }
    set
    {
        if (_criticalDate.Date != value)
        {
            if (_criticalDate != null && value != null && _criticalDate.Date == value)
               return;
            _criticalDate.Date = value;
            OnPropertyChanged("Date");
        }
    }
}