如何直接调用ReactiveUI 7中的ReactiveCommand.Execute（）是否正确？

Question

I'm trying to convert my project from ReactiveUI 6.5 to version 7. In the old version I called

// var command = ReactiveCommand.Create...;
// ...
if(command.CanExecute(null))
    command.Execute(null);

in order to execute a command from my code behind.

Now the CanExecute method is no longer available and replaced with a property of IObservable<bool> . Is the CanExecute Observable automatically called if I just make a call to Execute().Subscribe() or must I call it explicitly?

For now I replaced the above code with

command.Execute().Subscribe();

Answer 1

I found three different solutions to call my command's CanExecute and Execute methods like I could before in ReactiveUI 6.5:

Option 1

This is equal to the call in version 6.5, but we need to explicitly convert the command to an ICommand:

if (((ICommand) command).CanExecute(null))
    command.Execute().Subscribe();

Option 2

if(command.CanExecute.FirstAsync().Wait())
    command.Execute().Subscribe()

or the async variant:

if(await command.CanExecute.FirstAsync())
    await command.Execute()

Option 3

Another option is to make us of the InvokeCommand extension method.

Observable.Start(() => {}).InvokeCommand(ViewModel, vm => vm.MyCommand);

This respects the command's executability, like mentioned in the documentation .

---

In order to make it more comfortable I've written a small extension method to provide a ExecuteIfPossible and a GetCanExecute method:

public static class ReactiveUiExtensions
{
    public static IObservable<bool> ExecuteIfPossible<TParam, TResult>(this ReactiveCommand<TParam, TResult> cmd) =>
        cmd.CanExecute.FirstAsync().Where(can => can).Do(async _ => await cmd.Execute());

    public static bool GetCanExecute<TParam, TResult>(this ReactiveCommand<TParam, TResult> cmd) =>
        cmd.CanExecute.FirstAsync().Wait();
}

You can use this extension method as follows:

command.ExecuteIfPossible().Subscribe();

Note: You need the Subscribe() call at the end, just like you need it for the call to Execute() , otherwise nothing will happen.

Or if you want to use async and await:

await command.ExecuteIfPossible();

If you want to check if a command can be executed, just call

command.GetCanExecute()