We have a Xamarin.Forms app with FreshMvvm. Now, as Xamarin.Forms will not get support beginning next year, I am re-writing the app with .Net Maui. For MVVM pattern, I am trying to use CommunityToolkit.Mvvm. But I wonder how I can initialize the viewmodel now. With FreshMvvm I could override Init(), but CommunityToolkit.Mvvm does not seem to have anything like this. What is the right way to initialize the viewmodel asynchronously, as there is no async constructor?
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*"right way to initialize the viewmodel asynchronously"* What do you mean? Perhaps show a snippet of code, with a comment where you would add the "asynchronous" construction. – ToolmakerSteve Jul 22 '22 at 22:49
2 Answers
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In FreshMVVM, since the model has impelmented the FreshBasePageModel, you can override the Init() method and initialize data like the pseudo code below:
public override void Init (object initData)
{
//initialize data
}
However, in CommunityToolkit.Mvvm, you can set the data whatever you want in the default constructor like below:
public partial class MainPage : ContentPage
{
public MainPage(MainPageViewModel vm)
{
InitializeComponent();
BindingContext = vm;
Initialize();
}
public async void Initialize()
{
//await operation
}
}
Official reference link:https://learn.microsoft.com/en-us/windows/communitytoolkit/mvvm/introduction
Alexandar May - MSFT
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Thank you for your answer. But I need to call several async methods, so it would be good if I could call them from an async method. But constructor cannot be asynchronous. – David Shochet Jul 25 '22 at 10:12
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I've updated my answer. You can add an `async` method `Initialize();` in VM and then perform the `await` action. – Alexandar May - MSFT Aug 01 '22 at 03:00
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But as Initialize() is called synchronously, does it matter that it is async? – David Shochet Aug 01 '22 at 13:21
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I started with .net Maui a weeks ago and also needed the possibility to run async code in the constructor of the view model. I found the method SafeFireAndForget from AsyncAwaitBestPractices (nuget package). The async code will run in a different thread and the constructor may will complete before the async method.
Tobias Reißmann
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