MessagingCenter and NavigationService using reflection - xamarin

Question

I'm looking to improve my mobile application developed in Xamarin.Forms.
My functionality is as follows: onResume of the application I want to reload the page on which the user was.
Currently I use the MessagingCenter to operate with the code below.
Unfortunately my application is starting to have a lot of pages and it's not very readable anymore.
I am therefore looking to pass my type (viewModel) as a parameter of my navigation service - my research directs me towards the concept of reflection but I don't know if my problem is achievable.
// App.xaml.cs
protected override void OnResume()
{
// Handle when your app resumes
Page currPage = ((NavigationPage)((MasterDetailPage)Application.Current.MainPage).Detail).CurrentPage;
MessagingCenter.Send<App, Page>(this, "Hi", currPage);
}
Then in my BaseViewModel :
// BaseViewModel.cs
public ViewModelBase()
{
DialogService = ViewModelLocator.Instance.Resolve<IDialogService>();
NavigationService = ViewModelLocator.Instance.Resolve<INavigationService>();
AuthenticationService = ViewModelLocator.Instance.Resolve<IAuthenticationService>();
MessagingCenter.Subscribe<App, Page>(this, "Hi", async (sender, arg) =>
{
// Do something whenever the "Hi" message is received
Type viewModel = NavigationService.GetViewModelTypeForPage(arg.GetType());
if(viewModel == typeof(AboutViewModel))
{
Debug.WriteLine("AboutViewModel");
await NavigationService.NavigateToAsync<AboutViewModel>();
return;
}
if (viewModel == typeof(CardViewModel))
{
Debug.WriteLine("CardViewModel");
await NavigationService.NavigateToAsync<CardViewModel>();
return;
}
...
});
}

Answer 1

I would give you some ideas on how to make your code readable when using MessagingCenter.
First, you can have a BasePage which implemented the MessagingCenter.Subscribe and a method which called loadData:
public partial class BasePage : ContentPage
{
public BasePage()
{
MessagingCenter.Subscribe<App, string>(this, "Hi", (sender, arg) =>
{
// Do something whenever the "Hi" message is received
loadData();
});
}
public virtual void loadData()
{
}
}
Then, when you create a new page which need to refresh when the application is resumed, you can make the page inherits from the BasePage type:
public partial class MainPage : BasePage
{
public MainPage()
{
InitializeComponent();
loadData();
}
public override void loadData()
{
base.loadData();
Console.WriteLine("loadData");
}
}
And the xaml:
<?xml version="1.0" encoding="utf-8" ?>
<bases:BasePage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:d="http://xamarin.com/schemas/2014/forms/design"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:bases="clr-namespace:App52"
mc:Ignorable="d"
x:Class="App52.MainPage">
</bases:BasePage>
So you don't have to implement MessagingCenter.Subscribe in each Page, those can be managed in BasePage.
I'm not familiar with reflection so maybe can't help you on achieving that by reflection. Hope this helps.