Example of how to use MessagingCenter in Xamarin.Forms applications. - https://julianocustodio.com/messagingcenter

AddPage.xaml

<?xml version="1.0" encoding="UTF-8"?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms" 
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
             x:Class="DemoMessagingCenter.AddPage">
    <ContentPage.Content>
        <StackLayout Margin="10">
            <Entry Placeholder="Item" x:Name="EntryItem"/>
            <Button Clicked="Button_Clicked" 
                    Text="Add" 
                    BackgroundColor="#2196F3" 
                    TextColor="White"/>
        </StackLayout>
        
    </ContentPage.Content>
</ContentPage>