Caliburn micro 4 eventaggregator

Caliburn.Micro 4 EventAggregator

I was looking at some of the Caliburn Micro issues. https://github.com/Caliburn-Micro/Caliburn.Micro/issues/755 was looking for example on how to do best way to fire an Event Message during BaseScreen’s OnActivateAsync method

In this example I will have the shell view show a message on the MainView loading status

Here is the ShellView.xaml

<Window x:Class="Setup.WPF.Views.ShellView"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
         xmlns:cm="http://caliburnmicro.com"
         mc:Ignorable="d"
        Title="ShellView" Height="300" Width="300">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="25"></RowDefinition>
            <RowDefinition></RowDefinition>
        </Grid.RowDefinitions>
        <TextBlock Text="{Binding Message}"/>
        <ContentControl cm:View.Model="{Binding ActiveItem}" Grid.Row="1" Margin="40,20"/>
    </Grid>
</Window>

In the ShellViewModel I create the EventAggregator and register to receive the Publish events on the UI thread. When a message is recieved it will be shown in textblock

ShellViewModel.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Net.Http;
using System.Runtime.CompilerServices;
using System.Threading;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Threading;
using Caliburn.Micro;

namespace Setup.WPF.ViewModels
{
    public class ShellViewModel : Conductor<IScreen>.Collection.OneActive, IHandle<string>
    {
       private string _message;

       public string Message
       {
           get => _message;
           set
           {
               _message = value;
               NotifyOfPropertyChange("Message");
           }
       }


       private IEventAggregator _eventAggregator;
       public ShellViewModel()
       {
            _eventAggregator = new EventAggregator();
            _eventAggregator.SubscribeOnUIThread(this);
            Task.Run(async () =>
             {
                await ActivateItemAsync(new MainViewModel(_eventAggregator));
             });
       }


        public Task HandleAsync(string message, CancellationToken cancellationToken)
        {
            this.Message = message.ToString();
            return Task.CompletedTask;
        }


     }
 }

Here is the xaml for the MainView xaml

<UserControl x:Class="Setup.WPF.Views.MainView"
              xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
              xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
              xmlns:local="clr-namespace:Setup.WPF.Views"
               mc:Ignorable="d" 
               d:DesignHeight="450" d:DesignWidth="800">
    <Grid>
        <TextBlock Text="{Binding Title}"/>
    </Grid>
</UserControl>

The code for MainViewModel. It registers to publish events when the ViewModel loads. When the ViewIsActivating it sends a loading message. To simulate a long running task it uses Task.Delay to pause a few seconds. hen it clears the loading message

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using Caliburn.Micro;

namespace Setup.WPF.ViewModels
{
    public class MainViewModel : Screen
    {
        private string _title;

        public string Title
        {
             get => _title;
             set
             {
                _title = value;
                NotifyOfPropertyChange("Title");
              }
         }


        private IEventAggregator _eventAggregator;

         public MainViewModel(IEventAggregator eventAgg)
        {
            Title = "Welcome to Caliburn Micro in WPF";
            _eventAggregator = eventAgg;
          }

 
        protected override async Task OnDeactivateAsync(bool close, CancellationToken cancellationToken)
        {
             await _eventAggregator.PublishOnUIThreadAsync("Closing");
        }

         protected override async Task OnActivateAsync(CancellationToken cancellationToken)
        {
             await _eventAggregator.PublishOnUIThreadAsync("Loading");
             await Task.Delay(2000);
             await _eventAggregator.PublishOnUIThreadAsync(string.Empty);

        }


     }
 }

The source code is available on GitHub https://github.com/vb2ae/CM-Event-Aggregator