如何使用Reactive绑定到条目的“焦点”事件？

Question

I'm trying to bind to an text Entry fields "focused" event using reactive but my code is failing to compile.

Here's what I'm doing now, which works fine:

Entry _qty; // at class level
_qty.Focused += (s, e) => { /* do stuff */ };

Attempt

But I'd like to do something like this instead:

// class level

IObservable<string> _qtyFocusObservable;
Entry _qty;


// in a setup function

_qtyFocusObservable =
    Observable 
        .FromEventPattern<EventHandler<FocusEventArgs>>(
            x => _qty.Focused += x,
            x => _qty.Focused -= x
        );

Problem

I've tried quite a few variations of the code above and I get compiler errors saying that the compiler can't implicitly convert from whatever type I specify to System.EventHandler<System.EventHandler<Xamarin.Forms.FocusEventArgs>> , even if the type I specify is indeed System.EventHandler<System.EventHandler<Xamarin.Forms.FocusEventArgs>> .

Question

How do I bind to my Entry 's Focused event using reactive?

Answer 1

So to get a basic observable working from an event I usually structure like so:

var focusObservable = Observable.FromEventPattern<EventHandler, FocusEventArgs>( x => _qty.Focused += x.Invoke, x => _qty.Focused -= x.Invoke);

Then when I need to do something from that observable event I link a command to it like so:

var doStuffCommand = ReactiveCommand.CreateAsyncTask(DoStuffAsync); focusObservable.InvokeCommand(doStuffCommand);

With a DoStuffAsync implementation of something like this:

public async Task DoStuffAsync(object value, CancellationToken token = default(CancellationToken)) { // Do stuff here }

I'm still fairly new to Reactive as well but this (should?) get you going in the right direction.

Cheers, and happy coding!

Answer 2

So, after a year of using ReactiveUI, this is how I fire an event when focusing an input.

var focusedObservable =
    Observable
        .FromEventPattern<FocusEventArgs>(
            x => _totalBirds.Focused += x,
            x => _totalBirds.Focused -= x)
        .Select(x => x.EventArgs.IsFocused);

    // fires when focused
    focusedObservable 
        .WhenIsTrue() // extension method, basically .Where(x => x == true)
        .ObserveOn(RxApp.MainThreadScheduler)
        .InvokeCommand(this, x => DoSomething)
        .DisposeWith(ControlBindings); // extension that uses composite disposable

    // fires when changing state back to unfocused
    focusedObservable
        .WhenIsFalse() // extension method, basically .Where(x => x == false)
        .ObserveOn(RxApp.MainThreadScheduler)
        .InvokeCommand(this, x => x.ViewModel.DoSomethingElse)
        .DisposeWith(ControlBindings); // extension that uses composite disposable

This is pretty straight forward, if you need to see any additional code, let me know. Also, if you want to snag the .DisposeWith extension you can grab it here .