c# - Why is my event handler null? -


i've got quite simple problem gives me headache , i'm wasting time. i've ran out of ideas anyway:) reason can't pass value of property variable event handler. here i've got , me fine won't work:( enter image description here enter image description here

any idea why it's not passing actual value of variable? in advance:)

just name suggests, propertyname should contain property's name, not value. see propertychangedeventhandler , propertychangedeventargs on msdn more details.

as why event handler null, suspect haven't subscribed it. should have following somewhere in program:

obj.propertychanged += new propertychangedeventhandler(obj_propertychanged);  private void obj_propertychanged(object sender, propertychangedeventargs e) {   .... }

then when obj.moves changes obj_propertychanged called.

i understand confusion, let me give little more explanations. suppose have 2 classes a , b, , want b notified when property of a changed. can make a implement inotifypropertychanged, , make b subscribe propertychanged event of a, following:

public class a: inotifypropertychanged {   private int moves;   public int moves   {     { return moves; }     set     {       if (value != moves) {         moves = value;         onpropertychanged("moves");       }     }   }    public event propertychangedeventhandler propertychanged;    private void onpropertychanged(string propertyname)   {     if (propertychanged != null)       propertychanged(this, new propertychangedeventargs(propertyname));   } }  public class b {   private a = new a();    public b()   {     a.propertychanged += new propertychangedeventhandler(a_propertychanged);   }    private void a_propertychanged(object sender, propertychangedeventargs e)   {     ....   } }

with above, b.a_propertychanged called whenever a.moves changed. more precisely, if b instance of b, b.a_propertychanged called whenever b.a.moves changed. please note how implementation of setter of moves differs yours.


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