c# - MVVM Command selects the last added item -

i have viewmodel command. last added item editable command. makes sense when @ ode. it's not want. want selected item edited. i'll sketch problem:

i have model, named part

 public class part  {     private string _partcode;     private string _description;      public string partcode     {         { return _partcode.trim(); }         set { _partcode = value; }     }      public string description     {         { return _description; }         set { _description = value; }     }   } 

a viewmodel command, named partviewmodel

    /// <summary>     /// returns viewmodel containing parts.     /// </summary>     /// <param name="dt">database use.</param>     public partviewmodel(databasetype dt)     {         generateviewmodelforallparts(dt);     }     private async void generateviewmodelforallparts(databasetype dt)     {         using (nexuswcfserviceclient client = new nexuswcfserviceclient())             foreach (part item in await client.getallpartsasync(dt))             {                 _part = item;                 _items.add(item);             }     }     #endregion      #region members     private observablecollection<part> _items = new observablecollection<part>();      private part _part;     int count = 0;     #endregion      #region properties     public observablecollection<part> items     {         { return _items; }         set { _items = value; }     }      public part part     {         { return _part; }         set { _part = value; }     }      public string partcode     {         { return part.partcode; }         set         {             if (part.partcode != value) /* check if value changed */             {                 part.partcode = value;                 raisepropertychanged("partcode");  /* raise event */             }         }     }      public string description     {         { return part.description; }         set         {             if (part.description != value)             {                 part.description = value;                 raisepropertychanged("description");             }         }     }      #region commands     private void updatedescriptionexecute()     {         //count++;         //description = description + count.tostring();         // part.description = "asdasdasd";         messagebox.show(partcode);     }      private bool canupdatedescriptionexecute()     {         if (count >= 2)             return false;         else             return true;     }      public icommand updatedescription     {                 {             return new relaycommand(updatedescriptionexecute, canupdatedescriptionexecute);         }     }     #endregion } 

now whenever try fire command in de view:

<window x:class="nexuswpf.mainwindow"         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"         title="mainwindow" height="700" width="525" x:name="testview">     <grid>         <stackpanel x:name="stck">             <listview x:name="lb" itemssource="{binding items}">                 <listview.itemtemplate>                     <datatemplate>                         <stackpanel orientation="vertical" x:name="stck">                             <textblock text="{binding path=partcode}"/>                             <textblock text="{binding path=description}"/>                             <button content="update" datacontext="{binding elementname=testview, path=datacontext}" command="{binding updatedescription}" commandparameter="{binding}"/>                         </stackpanel>                     </datatemplate>                 </listview.itemtemplate>             </listview>         </stackpanel>     </grid> </window> 

the last added item (part) edited. makes sense because of following code in viewmodel:

 _part = item; 

how bind command selected item. guess there must wrong viewmodel , not in binding. _part get's overwritten everytime new part added. how can change work?

use relaycommand<part> accepts part command parameter:

public icommand updatedescription {         {         return new relaycommand<part>(updatedescriptionexecute, canupdatedescriptionexecute);     } }  private void updatedescriptionexecute(part part) {     messagebox.show(part.partcode); }  private bool canupdatedescriptionexecute(part part) {     if (count >= 2)         return false;     else         return true; } 

and modify command binding bit:

<button content="update" command="{binding datacontext.updatedescription,elementname=testview}" commandparameter="{binding}"/>