My menuitems in list view are not displaying Xamarin - xaml

Question

I've just started learning Xamarin, I have a problem while creating a listview. I want to create a button below each item in the list so I've seen that Xamarin gives you an option to create a button, MenuItem, but when I display my view it is not showed anywhere. This is the code of the listView, I believe that rest of the code is not necessary but if it is, I will edit.
<ListView x:Name="lvActivities" HasUnevenRows="True"
RelativeLayout.XConstraint="{ConstraintExpression
Type=RelativeToParent, Property=Width, Factor=0,Constant=0}"
RelativeLayout.YConstraint="{ConstraintExpression
Type=RelativeToParent, Property=Height, Factor=0.2,Constant=0}"
RelativeLayout.WidthConstraint="{ConstraintExpression
Type=RelativeToView, Property=Width, Factor=1, Constant=0,ElementName=rlAlumnInfo}"
RelativeLayout.HeightConstraint="{ConstraintExpression
Type=RelativeToParent, Property=Height, Factor=0.76, Constant=0}">
<ListView.ItemTemplate >
<DataTemplate >
<ViewCell >
<Grid >
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="*"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<Label Text="{Binding title}" FontSize="20" Grid.Row="0" Grid.Column="0" Margin="5,5,5,5" />
<StackLayout Grid.Row="0" Grid.Column="1" Orientation="Horizontal" Margin="5,5,5,5">
<Label Text="Aula :" FontSize="20"/>
<Label Text="{Binding cRoom}" FontSize="20" Margin="8,0,0,0"/>
</StackLayout>
<StackLayout Grid.Row="1" Grid.Column="0" Orientation="Horizontal" Margin="5,5,5,5" Grid.ColumnSpan="2">
<Label Text="Dia :" FontSize="20"/>
<Label Text="{Binding dateHour}" FontSize="20" Margin="8,0,0,0"/>
</StackLayout>
</Grid>
<ViewCell.ContextActions>
<MenuItem Text="Eliminar" Clicked="deleteActivity_Clicked" CommandParameter="{Binding .}"/>
</ViewCell.ContextActions>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>