A quick google search will find you a ton of information on this topic. Unfortunately the majority of them are simple path issues with a binding expression. I had a somewhat unique issue from a very simple mistake.
I had the following ComboBox:
<ComboBox Grid.Row="7" Grid.Column="1" Name="IptGpSalesPersonSlprsnid2" SelectedValue="{Binding Data.SLPersonId, ValidatesOnDataErrors=True}" ItemsSource="{Binding SalesPeople}" DisplayMemberPath="DisplayName" SelectedValuePath="SalesPersonId" />
This mostly did what I expected. It displayed "DisplayName" for the entire list of objects, it showed "SalesPersonId" as the SelectedValue, it would update another TextBox with the SelectedValue, and the selection could be changed by changing the SelectedValue in that TextBox. But for the life of me, it would not update the SLPersonId property on the "Data" object it was bound too.
"Data" is of type DynamicObject that I'm using as a binding proxy. I really didn't expect anything wrong with it since a TextBox bound to the same property would update the property without a problem. Still I trolled the overridable properties of DynamicObject and ended up adding the default overrides for the Equals and TryConvert methods. Sure enough, upon selecting a new item from the ComboBox, the debugger broke on "Equals." To my surprise, base.Equals was actually returning false. Why? This should be true since this was a reference type and I was returning the same object....damn....there's my problem...
In my view-model, my data property looked like this:
public DynamicProxy Data
{
get { return new DynamicProxy(this.data); }
}
I quickly added that code as a test and never made a variable to hold the new DynamicProxy instance.
Why ComboBox checks the variable instances to see if they are the same, i don't know, but since i look at what I did as bad code anyway, it doesn't really matter :P.
B