问题
Can someone help me resolve this problem I tried everything. I usually know how to resolve that problem but not with anonymous method. DelegateCommand has 2 constructors.
1) public DelegateCommand (Action executeMethod)
2) public DelegateCommand (Action executeMethod, Func canExecute).
I wanna know is it possible some how to remove that warning. Async and await are needed otherwise my method: enterButtonClicked(); would be called synchronously.
...
public DelegateCommand EnterButton { get; set; }
public StartPageViewModel()
{
Title = "title_black.png";
PasswordPlaceholder = "Lozinka";
EnterButton = new DelegateCommand( async () => { await enterButtonClicked();}); // <----- I am getting that warning here
}
public async Task enterButtonClicked()
{
}
...
回答1:
async await is only compatible with Func<Task> or Func<Task<T>> if you don't have that then you have what is considered a "Async void" which you should not do.
Your two options are to not await the task
...
public DelegateCommand EnterButton { get; set; }
public StartPageViewModel()
{
Title = "title_black.png";
PasswordPlaceholder = "Lozinka";
EnterButton = new DelegateCommand( () => { var temp = enterButtonClicked();});
}
public async Task enterButtonClicked()
{
}
...
which means any exceptions raised by enterButtonClicked will go unnoticed
or use a better delegate command that supports async functions. Personally I like the AsyncCommand from the Nito.Mvvm.Async NuGet package written by Stephen Cleary.
...
public AsyncCommand EnterButton { get; set; }
public StartPageViewModel()
{
Title = "title_black.png";
PasswordPlaceholder = "Lozinka";
EnterButton = new DelegateCommand(enterButtonClicked); //you can just use a delegate, no method needed.
}
public async Task enterButtonClicked()
{
}
...
The AsyncCommand delegate sets CanExecute to false while the task is running so a person can't repeatedly click unless the action has completed.
来源：https://stackoverflow.com/questions/46353690/asynchronous-method-anonymous-should-not-return-void