returning value item (not text item) in combobox.text [wpf C#] -

i have created custom class comboboxitem takes text/value , function return string.

public class comboboxitem {      public string text { get; set; }      public object value { get; set; }       public override string tostring()      {         return text;      } } 

i populate item , added combobox.

comboboxitem item = new comboboxitem(); item.text = result.codealias + " | " + result.description; item.value = result.codealias; combobox.items.add(item); 

and combobox shows both codealias + description in each item. i'm trying return codealias in content of box once user selects item instead of whole text

i tried following on selectionchanged of combobox.

combobox.text = (combobox.selecteditem comboboxitem).value.tostring(); 

and

combobox.selecteditem = (combobox.selecteditem comboboxitem).value.tostring(); 

and program crashes error:

object reference not set instance of object.

i put breakpoint , gets value doesn't set it. ideas how this?

item datacontext set viewsource since need load initial value table. here's xaml:

<combobox x:name="combobox" selectionchanged="combobox_selectionchanged"  datacontext="{staticresource mytableviewsource}" text="{binding myfield}" shell:windowchrome.ishittestvisibleinchrome="true" canvas.left="58" canvas.top="192" width="120"/> 

not smoothest ui experience, can swap displaymemberpath between text , value when combobox's dropdown opened/closed. meets criteria.

xaml

<combobox x:name="mycombobox" dropdownopened="mycombobox_dropdownopened" dropdownclosed="mycombobox_dropdownclosed" /> 

codebehind

private void mycombobox_dropdownopened(object sender, eventargs e) {     mycombobox.displaymemberpath = "text"; }  private void mycombobox_dropdownclosed(object sender, eventargs e) {     mycombobox.displaymemberpath = "value"; }