[c#] ComboBox SelectedItem vs SelectedValue

The following code works as you’d expect — MyProperty on the model is updated when the user picks a new item in the dropdown.

comboBox1.DataBindings.Add("SelectedValue", myModel, "MyProperty", true,
DataSourceUpdateMode.OnPropertyChanged);

The following, however, doesn’t work the same way and the model update isn’t triggered until the input focus moves to another control on the form:

comboBox1.DataBindings.Add("SelectedItem", myModel, "MyProperty", true, 
DataSourceUpdateMode.OnPropertyChanged);

Does anybody know why? I don’t even know where to start investigating the cause. Pointers in the right direction to start the investigation or an outright explanation would be equally appreciated.

Aside: for my purposes, I ended up binding to both SelectedItem and SelectedValue. This way I get instant model updates based on UI changes (through the SelectedValue binding), and UI updates based on programmatic model changes (through the SelectedItem binding).

If you want Selected.Value being worked you have to do following things:

1. Set DisplayMember
2. Set ValueMember
3. Set DataSource (not use Items.Add, Items.AddRange, DataBinding etc.)

The key point is Set DataSource!

This is a long-standing "feature" of the list controls in .NET in my experience. Personally, I would just bind to the on change of the SelectedValue property and write whatever additional code is necessary to workaround this "feature" (such as having two properties, binding to one for SelectedValue, and then, on the set of that property, updating the value from SelectedItem in your custom code).

Anyway, I hope that helps =D

If we want to bind to a dictionary ie

  <ComboBox SelectedValue="{Binding Pathology, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" 
                              ItemsSource="{x:Static RnxGlobal:CLocalizedEnums.PathologiesValues}" DisplayMemberPath="Value" SelectedValuePath="Key"
                              Margin="{StaticResource SmallMarginLeftBottom}"/>

then SelectedItem will not work whilist SelectedValue will

I suspect that the SelectedItem property of the ComboBox does not change until the control has been validated (which occurs when the control loses focus), whereas the SelectedValue property changes whenever the user selects an item.

Here is a reference to the focus events that occur on controls:

http://msdn.microsoft.com/en-us/library/system.windows.forms.control.validated.aspx