ComboBox SelectedItem vs SelectedValue

Question

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

User · Answer

If we want to bind to a dictionary ie     lt ComboBox SelectedValue   Binding Pathology  Mode TwoWay  UpdateSourceTrigger PropertyChanged                                  ItemsSource   x Static RnxGlobal CLocalizedEnums PathologiesValues   DisplayMemberPath  Value  SelectedValuePath  Key                                Margin   StaticResource SmallMarginLeftBottom    gt    then SelectedItem will not work whilist SelectedValue will

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

[c#] ComboBox SelectedItem vs SelectedValue

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