With thanks to Jan Van Der Haegen for his ExtensionsMadeEasy, without which I could not have achieved this. 
Basically, in Lightswitch, I wanted a button on the Ribbon that allows the user to view messages. The Button should update itself to reflect how many unread messages are available, like so:
First install Jan’s Extensions, which you can get here.
Then add the following code to the application.cs. This creates an event you can raise when a new message becomes available.
public partial class Application
{
public delegate void NewMessage();
public event NewMessage MessageReceived;
public void RaiseMessageReceived()
{
if (this.Details.Dispatcher.CheckAccess())
MessageReceived();
else
this.Details.Dispatcher.BeginInvoke(delegate()
{
MessageReceived();
});
}
}
Then you need the following code, which creates the command:
public class MessagesCommand : ExtensionsMadeEasy.ClientAPI.Commands.EasyCommandExporter
{
private int messageCount = 0;
public int MessageCount
{
get { return messageCount; }
set { messageCount = value; }
}
public new string Description
{
get { return string.Format("You have {0} message(s) waiting to be read", MessageCount); }
}
public new string DisplayName
{
get { return string.Format("Messages ({0})", MessageCount); }
}
public MessagesCommand() :
base("", "", "Screens",
new Uri(@"/ECSManager.Client;component/Resources/mail-128.png", UriKind.Relative))
{
base.Description = this.Description;
base.DisplayName = this.DisplayName;
Application.Current.MessageReceived += new Application.NewMessage(Current_MessageReceived);
}
void Current_MessageReceived()
{
// MessageReceived event is raised on the application's thread
// so need to do the UI update on a different thread
MessageCount++;
Microsoft.LightSwitch.Threading.Dispatchers.Main.BeginInvoke(() =>
{
base.DisplayName = this.DisplayName;
base.Description = this.Description;
});
}
public override void Execute(Microsoft.LightSwitch.Client.IScreenObject currentScreen)
{
// Open the Messages Screen (put your code here)
}
}
Scribbles Out.