c# - PropertyChangedEventHandler does not work -

i have following label , slider in usercontrol xaml

<label x:name="labelvalx" content="{binding path=xvalue}" horizontalalignment="left" width="88" height="44"/>   <slider x:name="sliderspeed" value="{binding slidevalue, mode=twoway}" horizontalalignment="left" margin="10,35,0,0" verticalalignment="top" width="173" height="53" minimum="10" maximum="100" /> 

and specific setgetaccvalues.cs class:

public class setgetaccvalues : usercontrol, inotifypropertychanged {      public event propertychangedeventhandler propertychanged;       private string _xval;     public string xvalue     {         { return _xval; }         set         {             if (value != _xval)             {                 _xval = value;                 onpropertychanged("xvalue");             }         }     }      public byte _slidevalue;       public byte slidevalue {                         {                 return _slidevalue;             }             set             {                 if (value != _slidevalue)                 {                     _slidevalue = value;                     onpropertychanged("slidevalue");                 }             }           }      protected virtual void onpropertychanged(string propname)    {       if (propertychanged != null)        {            propertychanged(this, new propertychangedeventargs(propname));            if (propname.equals("slidevalue"))            {            speedaccmeter(slidevalue);             }        }    } 

an in other getaccnotifications.cs class, have following part, i'm defining xvalue string specific value:

y = ((double)(sbyte)value) / 64.0; y = math.round(y, 2); setgetaccvalues set = new setgetaccvalues(); set.xvalue = y.tostring(); 

the problem occurs when onpropertychanged triggered "xvalue" propname, propertychangedeventhandler remains null, when triggered "slidevalue" propname not null. why remain null in xvalue case ?.

i believe propertychanged event firing before datacontext finished loading.

you can listen datacontextchanged event in usercontrol, when new datacontext available, can set properties.

public accview() {     initializecomponent();      this.datacontextchanged += ondatacontextchanged;      this.datacontext = new setgetaccvalues();     }  private void ondatacontextchanged(object sender, dependencypropertychangedeventargs dependencypropertychangedeventargs) {     y = ((double)(sbyte)value) / 64.0;     y = math.round(y, 2);      (dependencypropertychangedeventargs.newvalue setgetaccvalues).xvalue = y.tostring(); }