wpf - c# - 'an unhandled exception of type 'System.NullReferenceException' -

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• what nullreferenceexception, , how fix it? 32 answers

i'm newbie in mvvm, have model.cs contains few property of 'id' , 'positionname' , got view.cs contains datagrid selecteditems={binding items} , itemsource={binding position} , button command={binding showedits} after clicking encountered nullreference error @ 'items.positionname == null '.
here's code.

viewmodel.cs

class positionvm : inotifypropertychanged {     private observablecollection<positionmodel> _position;     private positionmodel _items;     private icommand _showedits;     public observablecollection<positionmodel> position     {                 {             return _position;         }         set         {             _position = value;             notifyproperty("position");         }     }     public positionmodel items     {                 {             return _items;         }         set         {             _items = value;             notifyproperty("items");         }     }     public icommand showedits     {                 {             if (_showedits == null)                 _showedits = new showedit();             return _showedits;         }         set         {             _showedits = value;         }     }     public positionvm()     {         position = new observablecollection<positionmodel>();         position.add(new positionmodel()         {             id = 1,             positionname = "asd"         });     }     public void showeditdialog()     {         if (items.positionname == null)         {             messagebox.show("error");         }         else         {             positionview view = new positionview();             data.id = view.txtid.text;             var z = new positionview();             z.showdialog();         }     }     public event propertychangedeventhandler propertychanged;     private void notifyproperty(string info)     {         if(propertychanged != null)         {             propertychanged(this, new propertychangedeventargs(info));         }     } } 

why getting error? , how can avoid it? thanksss

i think problem icommand. try property:

public icommand showeditscommand { get; set; }; 

and of course need create it. use command class it, can use on first time, it's pretty simple:

/// <summary> /// relay implementation of icommand. /// </summary> public class relaycommand : icommand {     private action execute;      private predicate<object> canexecute;      private event eventhandler canexecutechangedinternal;      public relaycommand(action execute)         : this(execute, defaultcanexecute)     {     }      public relaycommand(action execute, predicate<object> canexecute)     {         if (execute == null)         {             throw new argumentnullexception("execute");         }          if (canexecute == null)         {             throw new argumentnullexception("canexecute");         }          this.execute = execute;         this.canexecute = canexecute;     }      public event eventhandler canexecutechanged     {         add         {             commandmanager.requerysuggested += value;             this.canexecutechangedinternal += value;         }          remove         {             commandmanager.requerysuggested -= value;             this.canexecutechangedinternal -= value;         }     }      public bool canexecute(object parameter)     {         return this.canexecute != null && this.canexecute(parameter);     }      public void execute(object parameter)     {         this.execute();     }      public void oncanexecutechanged()     {         eventhandler handler = this.canexecutechangedinternal;         if (handler != null)         {             handler.invoke(this, eventargs.empty);         }     }      public void destroy()     {         this.canexecute = _ => false;         this.execute = () => { return; };     }      private static bool defaultcanexecute(object parameter)     {         return true;     } } 

after need initialize in viewmodel constructor , bind method:

showeditscommand = new relaycommand(showedits); 

where showedits methods need run when command call:

public void showedits() {  // here }