Question

I have a ComboBox that has I’ve created a binding to a List of items, but when I try to bind the selected item property, it doesn’t do anything. It used to work when I bound only the SelectedValueProperty. The class already implements INotifyPropertyChanged.

 public void ComboBoxBinding() {
      Dictionary<long, string> myDictionary = new Dictionary<long, string>
      Control control = new ComboBox();
      comboBoxControl = (ComboBox)control;
      comboBoxControl.SetBinding(ComboBox.ItemsSourceProperty, createFieldBinding("myDictionary"));
      comboBoxControl.DisplayMemberPath = "Value";
      comboBoxControl.SelectedValuePath = "Key";
      binding = createFieldBinding(fieldProperty);
      control.SetBinding(ComboBox.SelectedItemProperty, createFieldBinding("fieldProperty")); // <-- This doesn't seem to bind.
 }

 private Binding createFieldBinding(string propertyName) {
      Binding binding = new Binding(fieldName);
      binding.Source = this.DataContext;
      binding.UpdateSourceTrigger = System.Windows.Data.UpdateSourceTrigger.PropertyChanged;

 return binding;
 }

I set up a function that would change the dictionary variable, and the values in the ComboBox change, but I cannot get the SelectedValueProperty to change. How do I do that?

Edit: If I create a dictionary and set ItemsSource manually, it works, but when I set the binding, it doesn’t.

 Dictionary<long, string> myDictionary = new Dictionary<long, string>();
 myDictionary.Add(1, "test1");
 myDictionary.Add(2, "test2");
 myDictionary.Add(3, "test3");
 myDictionary.Add(4, "test4");
 myDictionary.Add(5, "test5");
 myDictionary.Add(6, "test6");
 myDictionary.Add(7, "test7");
 myDictionary.Add(8, "test8");
 myDictionary.Add(9, "test9");
 myDictionary.Add(10, "test10");
 comboBoxControl.ItemsSource = myDictionary; //<-- This works, but if I use Binding instead of manually setting the ItemsSource, it does not work

Answer 1

The reason it wasn’t binding was because I was defining the Dictionary in the ViewModel directly instead of creating a temporary Dictionary and setting it to the Property that implements INotifyPropertyChanged, which stops the Binding from recognizing the link between the member and the property a field was bound to.

Instead of doing:

 private Dictionary<long, string> _myList = new Dictionary<long, string>();
 public Dictionary<long, string> MyList {
      get { return _myList; }
      set { _myList = value;
            PropertyChanged("MyList"); }
 }

 public void Init() {
      _myList.Add(1, "One");
 }

I had to set a temporary Dictionary and apply that to the Property.

 private Dictionary<long, string> _myList = new Dictionary<long, string>();
 public Dictionary<long, string> MyList {
      get { return _myList; }
      set { _myList = value;
            PropertyChanged("MyList"); }
 }

 public void Init() {
      Dictionary<long, string> tempList = new Dictionary<long, string>();
      tempList.Add(1, "One");
      MyList = tempList;
 }