Contentpage.toolbaritems are not displaying in xamarin forms

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C#

forms

Xamarin

hi friends please help me
i am creating toolbar menu item in Xamarin forms. i have written codes MVVM.
my problem is that once i run the application to application is running properly but toolbar item contents are not displaying the menu items


if i create other project and applying same codes into different file so it is working properly but it is not showing in MVVM

What I have tried:

<ContentPage.ToolbarItems>
    <ToolbarItem Text="+"  Priority="0" Order="Primary"  IconImageSource="menu.png"></ToolbarItem>
</ContentPage.ToolbarItems>