How can I use async in an mvvmcross view model?
async-await, c#, mvvmcross, xamarin
Solution
You should avoid `async void`. When you're dealing with `ICommand`, you do need to use `async void`, but its scope should be minimized.
This modified code exposes your action as an `async Task`, which is unit testable and consumable from other parts of your code:
public class MyModel: MvxViewModel
{
private readonly IMyService _myService;
private bool _isBusy;
public bool IsBusy
{
get { return _isBusy; }
set { _isBusy = value; RaisePropertyChanged(() => IsBusy); ; }
}
public ICommand MyCommand
{
get
{
return new MvxCommand(async () => await DoMyCommand());
}
}
public MyModel(IMyService myService)
{
_myService = myService;
}
public async Task DoMyCommand()
{
IsBusy = true;
await Task.Run(() =>
{
_myService.LongRunningProcess();
});
IsBusy = false;
}
}
Your use of `IsBusy` is fine; that's one common approach in asynchronous UIs.
I did change `Task.Factory.StartNew` to `Task.Run`; `Task.Run` is preferred in `async` code for reasons described by Stephen Toub.
Problem
I have a long running process in an mvvmcross viewmodel and wish to make it async (http://msdn.microsoft.com/en-us/library/vstudio/hh191443.aspx). The async keyword is currently supported in the beta channel for Xamarin. Below is an example of how I'm currently implementing async. The IsBusy flag ccould be bound to a UI element and display a loading message. Is this the correct way? ``` public class MyModel: MvxViewModel { private readonly IMyService _myService; private bool _isBusy; public bool IsBusy { get { return _isBusy; } set { _isBusy = value; RaisePropertyChanged(() => IsBusy); ; } } public ICommand MyCommand { get { return new MvxCommand(DoMyCommand); } } public MyModel(IMyService myService) { _myService = myService; } public async void DoMyCommand() { IsBusy = true; await Task.Factory.StartNew(() => { _myService.LongRunningProcess(); }); IsBusy = false; } } ```