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).
The ComboBox
control inherits from the ListControl
control.
The SelectedItem
property is a proper member of the ComboBox
control. The event that is fired on change is ComboBox.SelectionChangeCommitted
ComboBox.SelectionChangeCommitted
Occurs when the selected item has changed and that change is displayed in the ComboBox.
The SelectedValue
property is inherited from the ListControl
control.
As such, this property will fire the ListControl.SelectedValueChanged
event.
ListControl.SelectedValueChanged
Occurs when the SelectedValue property changes.
That said, they won't fire the INotifyPropertyChanged
.PropertyChanged
event the same, but they will anyway. The only difference is in the firing event. SelectedValueChanged
is fired as soon as a new selection is made from the list part of the ComboBox, and SelectedItemChanged
is fired when the item is displayed in the TextBox portion of the ComboBox.
In short, they both represent something in the list part of the ComboBox. So, when binding either property, the result is the same, since the PropertyChanged
event is fired in either case. And since they both represent an element from the list, the they are probably treated the same.
Does this help?
EDIT #1
Assuming that the list part of the ComboBox represents a property (as I can't confirm since I didn't write the control), binding either of SelectedItem
or SelectedValue
affects the same collection inside the control. Then, when this property is changed, the same occurs in the end. The INotifyPropertryPropertyChanged.PropertyChanged
event is fired on the same property.