Observable on ReactiveCollection count change

[Sotirios Mantziaris]

Hi,

i want to create a command that is enabled only when a collection contains any items.

public ReactiveCollection<PositionViewModel> NewPositions { get; protected set; }

and the command would be:

public ReactiveCommand ClearPositionCommand { get; private set; }

following the examples i should do something like this:

var canClearPosition = this.WhenAny(x => x.NewPositions, pass => (pass.Value.Count > 0));

ClearPositionCommand = new ReactiveCommand(canClearPosition);

but this doesnt seem to work.

Any suggestions?

[Lukáš Čenovský]

It should be:

ClearPositionCommand = new
ReactiveCommand(NewPositions.ColectionCountChanged);

WhenAny watches NewPositions change - e.g. when you assign different
collection to it.

--
-- Lukáš

[Sotirios Mantziaris]

ok,

but NewPositions.ColectionCountChanged is a Observable<int> and not Observable<bool> which is required in the constructor.

what i actualy need is a Observable<bool> that return true if the NewPositions has Count != 0 else false.

Any suggestions?

[Paul Betts]

How about

Clear = new ReactiveCommand(NewPositions.ColectionCountChanged.Select(x
=> x > 0));

--
Paul Betts <pa...@paulbetts.org>

[Lukáš Čenovský]

What about this minor update? ;-)

NewPositions.ColectionCountChanged.Value().Select(cnt => cnt > 0)

--
-- Lukáš

[Paul Betts]

CollectionCountChanged's type is just IO<int>, you don't need the Value()

2011/12/28 Lukáš Čenovský <lcen...@gmail.com>:

[Lukáš Čenovský]

Oh yes - that happens when you write it from mind instead of testing it :-)

[Sotirios Mantziaris]

Paul, that is the reason i didnt find the Value(). 

Your solution did not work either! Am i something missing?

ClearPositionCommand = new ReactiveCommand(NewPositions.CollectionCountChanged.Select(x=>x>0));

ClearPositionCommand.Subscribe(o=>{ClearPosition();}, OnError, OnCompleted);

[Paul Betts]

This should definitely work. Are you overwriting NewPositions
somewhere? i.e. somewhere other than the constructor, writing:

NewPositions = new ReactiveCollection<Foo>();

Another thing you probably need to do is:

NewPositions.CollectionCountChanged.StartWith(0).Select(x => x > 0)

--
Paul Betts <pa...@paulbetts.org>

[Lukáš Čenovský]

Mind that calling NewPositions.Clear() does not trigger count change. It
is unfortunate but according to spec....

[Sotirios Mantziaris]

Paul the StartsWith(0) worked and the command is now ok. thx

Lukas i saw that Clear didnt work. What is the alternative?

[Sotirios Mantziaris]

lukas , a straightforward for loop did the job!!!

Thanks for the help!

[Sotirios Mantziaris]

Paul thx for the help, really like it once you can get your head around the idea of getting the data pushed to you!!

I am following with great joy!