How I can safely run async code, when handling messages from Messenger?

I am using MVVM, inparticular MVVMLight. For boradcasting to all of my modelviews, that no internet connection is available I am using Messenger class. The modelviews subscribe to this event in order to reload itself with offline data, inform user etc.

However, I have a problem. When I have the folowing handler:

private void HandleNoInternetMessage(NoInternetAccessMessage obj)
{
    Task.Run(async () => await InitializeForOfflineInternalAsync());
}
public async Task InitializeForOfflineInternalAsync()
{
    try
    {
        WaitingLayerViewModel.ShouldBeVisible = true;
        WaitingLayerViewModel.IsBusy = true; //<--exception HRESULT: 0x8001010E (RPC_E_WRONG_THREAD)
        bool switchToOffline = await CommonViewModelProvider.InformUserOfNoInternetAccessAndChangeAppState(); //<!- CoreWindow.GetForCurrentThread().Dispatcher is null
        await FilterTestItemViewModel.InitializeForOfflineAsync();
        await FilterTestItemViewModel.InitializeForOfflineAsync();
        WaitingLayerViewModel.ShouldBeVisible = false;
        WaitingLayerViewModel.IsBusy = false;
        ...
    }
}

I got exception HRESULT: 0x8001010E (RPC_E_WRONG_THREAD), because in InitializeForOfflineInternalAsync I am changing some properties of the viewmodel wchich are bound in XAML (or at least I think it is because of that). However, it is weird, because I am changing in other code bound properties regularly and have no problems with it (and the thread is a working thread).

Now, how can i solve that?

• The messanger let me provide only delegate which is not async (which make kind of sense), so I can not have the HandleNoInternetMessage method async

• I am using async await ... no explicit spawning of threads

• I dont have access in VM to Dispatcher, because I am in VM which should not know about platform dependent stuff. And when I tried to use it to show a message, NullPointer excpetion was thrown when calling CoreWindow.GetForCurrentThread().Dispatcher; And again when calling from other places, no such exception was thrown

I guess the question is How I can safely run async code, which changes boudn properties, when handling messages from Messenger?

You're responding to messages that are logically events, so this is an acceptable use case for async void.

private async void HandleNoInternetMessage(NoInternetAccessMessage obj)
{
    await InitializeForOfflineInternalAsync();
}

public async Task InitializeForOfflineInternalAsync()
{
    try
    {
        WaitingLayerViewModel.ShouldBeVisible = true;
        WaitingLayerViewModel.IsBusy = true;
        bool switchToOffline = await CommonViewModelProvider.InformUserOfNoInternetAccessAndChangeAppState();
        await FilterTestItemViewModel.InitializeForOfflineAsync();
        await FilterTestItemViewModel.InitializeForOfflineAsync();
        WaitingLayerViewModel.ShouldBeVisible = false;
        WaitingLayerViewModel.IsBusy = false;
        ...
    }
}

Remember that Task.Run is for CPU-bound code (as I describe on my blog).