c# - Caliburn resetting SelectedIndex on ComboBox -

i have combobox has itemssource bound list of items in viewmodel selecteditem being bound property. have combobox bound list, uses selectedindex instead. when select item first combobox, changes contents of seconds combobox, , property bound selectedindex gets set -1, causes nothing selected in combobox.

why selectedindex property reset -1, , can prevent it?

view

<combobox itemssource="{binding mylist}" selecteditem="{binding myselecteditem}"></combobox> <combobox itemssource="{binding myarray}" selectedindex="{binding myselectedindex}"></combobox> 

viewmodel

public list<foo> mylist { get; set; } private foo _myselecteditem; public foo myselecteditem {     { return _myselecteditem; }     set {         if (equals(value, _myselecteditem)) return;         _myselecteditem = value;         notifyofpropertychange();         myarray = new [] { "othervalue1", "othervalue2", "othervalue3" };         notifyofpropertychange(() => myarray);     } } public string[] myarray { get; set; } public int myselectedindex { get; set; }  public myviewmodel() {     mylist = new list<foo> { new foo(), new foo(), new foo() };     myselecteditem = mylist.first();      myarray = new [] { "value1", "value2", "value3" };     myselectedindex = 1; // "value2"      notifyofpropertychange(() => mylist); } 

so, selecting combobox bound mylist causes myarray built new values. causes myselectedindex have value -1, though same indices exist in new array.

the selecteditem indeed reset because selected item cleared out when itemssource property set new collection of items.

but should able store index in temporary variable , re-assign after itemssource has been updated:

public foo myselecteditem {     { return _myselecteditem; }     set     {         if (equals(value, _myselecteditem)) return;         _myselecteditem = value;         notifyofpropertychange();         int temp = myselectedindex;         myarray = new[] { "othervalue1", "othervalue2", "othervalue3" };         notifyofpropertychange(() => myarray);          selectedindex = temp;         notifyofpropertychange(() => selectedindex);     } }