c# - WPF window doesn't get updated by property binding -

i have wpf form textbox defined in xaml file follows:

<textbox grid.column="1"  grid.row="9" tabindex="0" x:name="txtboxexample" width="170" >     <textbox.style>         <style targettype="{x:type textbox}">             <setter property="visibility" value="hidden" />             <style.triggers>                 <datatrigger binding="{binding tooldatacontext.iteminstance.istoshow, mode=twoway}" value="true">                     <setter property="visibility" value="visible" />                 </datatrigger>             </style.triggers>         </style>     </textbox.style>     <textbox.text>         <binding path="tooldatacontext.iteminstance.usertext" updatesourcetrigger="propertychanged" />           </textbox.text> </textbox> ... <button click="somebtn_click" content="{x:static res:strings.buttonstring}" name="somebutton"> 

on xaml.cs file have following code:

private void somebtn_click(object sender, routedeventargs e) {     ...     tooldatacontext.iteminstance.istoshow = true;     ... } 

in item class have following code property istoshow:

public class item : syncableobject, isearchableobject, inotifypropertychanged {     ...      private bool _istoshow;     public bool istoshow     {         { return _istoshow; }         set         {             if (value == _istoshow)                 return;              _istoshow = value;             this.onpropertychanged("istoshow");                         }     }      ...      new public event propertychangedeventhandler propertychanged;     new public void onpropertychanged(string propertyname)     {         propertychangedeventhandler handler = this.propertychanged;         if (handler != null)             handler(this, new propertychangedeventargs(propertyname));     }      ... } 

i expect window show textbox when click when on button. doesn't happen.

can give me lead doing wrong?

try adding path data trigger binding

<datatrigger binding="{binding path=tooldatacontext.iteminstance.istoshow, mode=twoway}" value="true">