c# - WPF Dynamic TabControl SelectionChanged bug? -

i creating simple application using c# , wpf using mvvm pattern. there main window few buttons , contentcontrol containing list of view models, 1 of them being searchviewmodel. buttons flip between view models.

the searchviewmodel bound searchview , contains tabcontrol. itemssource property bound list of searchtabviewmodels. in constructor of searchviewmodel, initializing observablecollection of searchtabviewmodels , adding 2 tabs. first tab has "+" header , other normal search tab. tabcontrol's selectionchanged event bound method checks if "+" tab clicked. if is, new tab inserted before "+" tab , tabcontrol's selectedindex property set index of inserted tab. simple setup.

the issue i'm having when application first run, can click "+" tab , insert new tab "+" tab dead , nothing happens when click it. selectionchanged event not fire. i've checked , selectedindex set tab before it's not selected tab. fix it, have click on tab first , works fine. freezes once @ beginning.

can see issue may be? i'm including relevant portions of code:

xaml

<tabcontrol      name="searchtabcontrol" itemssource="{binding path=searchtabs}"     selectedindex="{binding path=selectedtabindex}"     itemtemplateselector="{binding source={staticresource searchtabtemplateselector}}">      <i:interaction.triggers>         <i:eventtrigger eventname="selectionchanged" >             <i:invokecommandaction                  commandname="searchtabhaschanged" command="{binding selectionchangedcommand}"                 commandparameter="{binding relativesource={relativesource self}, path=commandname}"/>         </i:eventtrigger>     </i:interaction.triggers>     ....more code 

searchviewmodel

public class searchviewmodel : observableobject, ipageviewmodel {     #region fields      public observablecollection<searchtabviewmodel> searchtabs { get; set; }     private int _selectedtabindex;     private icommand _selectionchangedcommand;      #endregion      public searchviewmodel()     {         try         {             // initialize searchtabs array             this.searchtabs = new observablecollection<searchtabviewmodel>();              // add tabitem + in header              searchtabviewmodel tabadd = new searchtabviewmodel("+");              this.searchtabs.add(tabadd);              // add first tab             addtabitem();              selectedtabindex = 0;         }         catch (exception ex)         {             messagebox.show(ex.message);         }     }      #region properties/commands      public int selectedtabindex     {         { return _selectedtabindex; }         set         {             _selectedtabindex = value;             onpropertychanged("selectedtabindex");         }     }      public icommand selectionchangedcommand     {                 {             if (_selectionchangedcommand == null)             {                 _selectionchangedcommand = new relaycommand(                     param => tabselectionchanged(param)                 );             }             return _selectionchangedcommand;         }     }      #endregion      #region methods      public void tabselectionchanged(object source)     {         if (source.tostring() == "searchtabhaschanged")         {             searchtabviewmodel tab = this.searchtabs[selectedtabindex];              if (tab != null && tab.header != null)             {                 if (tab.header.equals("+"))                 {                     // add new tab                     searchtabviewmodel addedtab = addtabitem();                      // select newly added tab item                     selectedtabindex = this.searchtabs.indexof(addedtab);                 }             }         }     }      private searchtabviewmodel addtabitem()     {         int count = searchtabs.count;          // create new tab item         searchtabviewmodel tab = new searchtabviewmodel();         tab.header = string.format("tab {0}", count);          // insert tab item right before last (+) tab item         this.searchtabs.insert(count - 1, tab);          return tab;     }      #endregion } 

also, curious behavior i've noticed when first run application , click "+" tab once add new tab , "+" tab dies, if application loses focus , gains focus again, selectionchanged event fires , new tab added? behavior happens when "+" tab dead. once fix clicking on tab, behavior disappears.

in tabselectionchanged, add new tabitem , change selectedtabindex right after each other. problem itemcontainergenerator generates new tabitem in view has not been triggered yet. done in databinding phase. when set selectedtabindex, set (already selected) + tab.

to fix this, postpone changing of selectedtabindex invoking call on dispatcher priority lower databinding.

this.dispatcher.begininvoke(() => selectedtabindex = this.searchtabs.indexof(addedtab), dispatcherpriority.background);