c# - PropertyChanged for a custom class is always null -

i have problem inotifypropertychanged , binding, watched dozen questions here, problem still exists.

my xaml code:

<window x:class="daa.ist.choosepc.mainwindow"     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"     xmlns:d="http://schemas.microsoft.com/expression/blend/2008"     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"     xmlns:local="clr-namespace:daa.ist.choosepc"     mc:ignorable="d"     title="mainwindow" height="350" width="525"> <window.resources>     <local:question x:key="expertsystem" text="question"/> </window.resources> <grid datacontext="{staticresource expertsystem}">     <label x:name="description" content="Определение опимальной конфигурации ПК" horizontalalignment="left" margin="100,30,0,0" verticalalignment="top"/>     <button x:name="button" content="" horizontalalignment="left" margin="204,167,0,0" verticalalignment="top" width="75" click="button_click"/>     <button x:name="button1" content="" horizontalalignment="left" margin="284,167,0,0" verticalalignment="top" width="75" click="button1_click"/>     <label x:name="questionlable" content="{binding text}" horizontalalignment="left" margin="100,70,0,0" verticalalignment="top"/>     <label x:name="result" content="" horizontalalignment="left" margin="100,210,0,0" verticalalignment="top"/>  </grid> 

i list here full code, because don't know there problem is, sorry. main window code:

public partial class mainwindow : window {     public static iquestion question;      public mainwindow()     {         initializecomponent();         question = new question         {             text = "question",             answers = new list<ianswer>                       {                           new answer {text = "answer", nextquestionnumber = 0},                           new answer {text = "answer1", nextquestionnumber = 0}                       }         };         datacontext = question;     }      private void button_click(object sender, routedeventargs e)     {         question.answer(0);     }      private void button1_click(object sender, routedeventargs e)     {         question.answer(1);     } } 

and questioncode, class implements inotifypropertychanged:

public class question : iquestion, inotifypropertychanged {     private string _text;      public string text     {         { return _text; }         set         {             _text = value;             onpropertychanged("text");         }     }       public ilist<ianswer> answers { get; set; }      public void answer(int number)     {         mainwindow.question.answers[number].number = number;         mainwindow.question.answers[number].setnextquestion();     }      public event propertychangedeventhandler propertychanged;      [notifypropertychangedinvocator]     protected virtual void onpropertychanged([callermembername] string propertyname = null)     {         propertychanged?.invoke(this, new propertychangedeventargs(propertyname));     } } 

please me, sure miss or don't know something. if can give me advise changing of ilist<ianswer> answers, thankful him^^

first of all, bad practice refer mainwindow inside question class. should use commands in context i.e. should define command in datacontext( question here) , bind command 2 button's command property.

for example:

class question : inotifypropertychanged, iquestion {   public icommand buttonclickcommand { get; set;}    public question()   {     //bind buttonclickcommand event handler/ method     buttonclickcommand = new delegatecommand(eventhandlername);   }   public void eventhandlername()   {   } } 

also, take private _answers field in class , raise onpropertychanged event setter of answers property too, utilize list in notification mechanism i.e.

public ilist<ianswer> answers {    { return _answers }   set { _nswers = value;   onpropertychanged("answers"); 

}

and, have mentioned want chnge content of label , buttons. change content of label , buttons, need bind 'content' of these controls properties in question class well. don't see binding in xaml of now.