xaml - Xamarin command is not working for object of Observablecollection -

i new xamarin , working on solution in facing below problem. have class model class, , class b viewmodel. model class

class  : inotifypropertychanged {    public string sampleprop { get; set; }    public event propertychangedeventhandler propertychanged;    public virtual void onpropertychanged(string propertyname)         {             if (propertychanged == null)                 return;         propertychanged(this, new propertychangedeventargs(propertyname));         } } 

i creating objects of class observable collection in class b.

class b     {    public command<string> callcommand { get; set; }    public observablecollection<a>   aobjectscollection { get; set; }     public b()         {             aobjectscollection = new observablecollection<a>();             callcommand = new command<string>((string arg) =>      domakecall(arg));         }     public void domakecall(string phnumber)         {             string s = phnumber;         } } 

assigning class b binding context main view page.

public partial class mainview : contentpage  {     initializecomponent ();          bindingcontext = new b();   } 

in main view(xaml) creating listview classb's observable collection property.

     <listview x:name="messageslistview"                   itemssource="{binding aobjectscollection }"                  hasunevenrows="true" >                  <listview.itemtemplate>                    <datatemplate>                      <viewcell >                          <viewcell.view>              <button x:name="btnclick" text="clickme"                      command="{binding callcommand}"                      commandparameter="sampleprop"/>               </viewcell.view>                          </viewcell>                    </datatemplate>                  </listview.itemtemplate>       </listview> 

now clicking on button(btnclick) in main page not invoking command of viewmodel , execute method domakecall(string s).

could please me understand on wrong in code? , how can achieve scenario?

my command property vm class , not in model class. thing need find out how set context make work. don't want use relay command.

you're binding each viewcell model. has no reference b viewmodel (which command resides want call. fix this, need tell viewcell button command on messageslistview's bindingcontext (your b viewmodel in case). this:

bindingcontext="{binding source={x:reference messageslistview}, path=bindingcontext}" 

and in full context:

 <listview x:name="messageslistview"             itemssource="{binding aobjectscollection }"            hasunevenrows="true" >            <listview.itemtemplate>                <datatemplate>                    <viewcell x:name="viewcell">                        <viewcell.view>                            <button x:name="btnclick" text="clickme"                                  bindingcontext="{binding source={x:reference messageslistview}, path=bindingcontext}"                                   command="{binding callcommand}"                                   commandparameter="{binding source={x:reference viewcell}, path=bindingcontext}"/>                         </viewcell.view>                    </viewcell>                </datatemplate>            </listview.itemtemplate> </listview>