MessengerRequestPage.xaml

<Page
    x:Class="MvvmSampleUwp.Views.MessengerRequestPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:controls="using:MvvmSampleUwp.Controls"
    xmlns:core="using:Microsoft.Xaml.Interactions.Core"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:interactivity="using:Microsoft.Xaml.Interactivity"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
    xmlns:mvvmSampleUwp="using:MvvmSampleUwp"
    NavigationCacheMode="Enabled"
    mc:Ignorable="d"
    mvvmSampleUwp:ViewModelLocator.InitViewModel="True">
    <interactivity:Interaction.Behaviors>
        <core:EventTriggerBehavior EventName="Loaded">
            <core:InvokeCommandAction Command="{x:Bind ViewModel.LoadDocsCommand}" CommandParameter="Messenger" />
        </core:EventTriggerBehavior>
    </interactivity:Interaction.Behaviors>

    <ScrollViewer Padding="{StaticResource DocumentationPageContentPadding}" CanContentRenderOutsideBounds="True">
        <StackPanel Spacing="16">
            <controls:DocumentationBlock Text="{x:Bind ViewModel.GetParagraph('Using request messages'), Mode=OneWay}" />

            <controls:InteractiveSample xml:space="preserve">
                <controls:InteractiveSample.Content>
                    <StackPanel xml:space="default" Spacing="8">

                        <TextBlock Text="{x:Bind ViewModel.Username, Mode=OneWay}" />
                        <Button Click="{x:Bind ViewModel.RequestCurrentUsername}" Content="Click to request the username!" />
                        <Button Click="{x:Bind ViewModel.ResetCurrentUsername}" Content="Click to reset the local username!" />
                    </StackPanel>
                </controls:InteractiveSample.Content>
                <controls:InteractiveSample.XamlCode>
&lt;StackPanel Spacing=&quot;8&quot;&gt;
    &lt;TextBlock Text=&quot;{x:Bind ViewModel.Username, Mode=OneWay}&quot;/&gt;
    &lt;Button
        Content=&quot;Click to request the username!&quot;
        Click=&quot;{x:Bind ViewModel.RequestCurrentUsername}&quot;/&gt;
    &lt;Button
        Content=&quot;Click to reset the local username!&quot;
        Click=&quot;{x:Bind ViewModel.ResetCurrentUsername}&quot;/&gt;
&lt;/StackPanel&gt;
                </controls:InteractiveSample.XamlCode>
                <controls:InteractiveSample.CSharpCode>
// Simple viewmodel for a module responding to a request username message.
// Don't forget to set the IsActive property to true when this viewmodel is in use!
public class UserSenderViewModel : ObservableRecipient
{
    public string Username { get; private set; } = &quot;Bob&quot;;

    protected override void OnActivated()
    {
        Messenger.Register&lt;UserSenderViewModel, CurrentUsernameRequestMessage&gt;(this, (r, m) =&gt; m.Reply(r.Username));
    }
}

private string username;

public string Username
{
    get =&gt; username;
    private set =&gt; SetProperty(ref username, value);
}

// Sends a message to request the current username, and updates the property
public void RequestCurrentUsername()
{
    Username = WeakReferenceMessenger.Default.Send&lt;CurrentUsernameRequestMessage&gt;();
}

// Resets the current username
public void ResetCurrentUsername()
{
    Username = null;
}

// A sample request message to get the current username
public sealed class CurrentUsernameRequestMessage : RequestMessage&lt;string&gt;
{
}
                </controls:InteractiveSample.CSharpCode>
            </controls:InteractiveSample>
        </StackPanel>
    </ScrollViewer>
</Page>