Don't thrown when tap/selected is null, return null. For deselect.

[jamesmontemagno]

Description of Change

For example I want to write this in my VM:

        Coffee selectedCoffee;
        public Coffee SelectedCoffee
        {
            get => selectedCoffee;
            set => SetProperty(ref selectedCoffee, value);
        }

        async Task Selected(Coffee coffee)
        {
            if (coffee == null)
                return;

            await Application.Current.MainPage.DisplayAlert("Selected", coffee.Name, "OK");
            SelectedCoffee = null;
        }

And this in my XAML:

    <ListView
        SelectedItem="{Binding SelectedCoffee, Mode=TwoWay}"
>
        <ListView.Behaviors>
            <xct:EventToCommandBehavior
                Command="{Binding SelectedCommand}"
                EventArgsConverter="{StaticResource ItemSelectedEventArgsConverter}"
                EventName="ItemSelected" />
        </ListView.Behaviors>

Today, this will throw an exception because it it null and is not of the type it is expecting, but that should be allowed.

The only work around is to do something like AsyncCommand<object> instead of AsyncCommand<Coffee>

Bugs Fixed

• Fixes #

API Changes

Behavioral Changes

PR Checklist

• Has tests (if omitted, state reason in description)
• Has samples (if omitted, state reason in description)
• Rebased on top of main at time of PR
• Changes adhere to coding standard

• Updated documentation

[pictos]

@jamesmontemagno thanks for this PR, can you rephrase this part, I'm a little lost in there

The only work around is to do something like AsyncCommand instead of AsyncCommand

[jamesmontemagno]

Whoops -> AsyncCommand<object> instead of AsyncCommand<Coffee>

[jamesmontemagno]

The problem is when you set "SelectedCoffee = null" in the Command it throws an exception because this code is false:
value is SelectedItemChangedEventArgs selectedItemChangedEventArgs

so you need to check to see if value is null first.

[jamesmontemagno]

I wasn't able to run tests locally, so someone probably needs to pull this PR down.

[pictos]

I can do it!

[jamesmontemagno]

Fixed up my example

[jamesmontemagno]

Take a look here -> https://github.com/jamesmontemagno/MyCoffeeApp/blob/master/MyCoffeeApp/MyCoffeeApp/ViewModels/CoffeeEquipmentViewModel.cs#L61

I should be able to do AsyncCommand<Coffee> and also async Task Selected(Coffee coffee). This works fine until I do SelectedCoffee = null

[pictos]

Yeah, I can confirm that the problem is the null return in the converter, to fix that we need to think in a way to know what is the type of SelectedItemChangedEventArgs.SelectedItem and ItemTappedEventArgs.Item, to cast that null to them.

Obs.: XCT.AsyncCommand also throws the same exception.

[pictos]

@jamesmontemagno I was able to fix it on XCT but is a very ugly fix. So I would say that is a known bug and the workaround is using the object as a parameter. The null check that you added on converters is enough, I believe. Can we merge this?

[jfversluis]

Thanks James! <3

[jamesmontemagno]

Did this actually fix the full bug or does AsyncCommand also need to be patched?

[pictos]

@jamesmontemagno the fix will be on EventToCommandBehavior, you can see my spec here #953, if you have time, please let me know what you think about it (:

[jamesmontemagno]

Ahhh gotcha! cool! Did my code do anything? I saw @jfversluis pulled it in.. :)

[pictos]

@jamesmontemagno I tested yesterday using your code and works like a charm. Now is just a matter to see if my idea is good and safe to implement (:

[jamesmontemagno]

Gotcha, so it will be a combination of your fix and my fix that fixes it up fully for me. Got it

[thecuong064]

I'm using XCT version 1.2.0 and still facing this issue. Is there anything else I'm missing?

This is my code.

<ListView
SelectedItem="{Binding SelectedItem, Mode=TwoWay}">

<ListView.Behaviors>
    <xct:EventToCommandBehavior
        Command="{Binding SelectItemCommand}"
        EventArgsConverter="{StaticResource ItemSelectedEventArgsConverter}"
        EventName="ItemSelected" />
</ListView.Behaviors>

private Item selectedItem;
public Item SelectedItem 
{ 
    get => selectedItem;
    set => SetProperty(ref selectedItem, value);
}

public AsyncCommand<Item> SelectItemCommand { get; }
private async Task ExecuteSelectItemCommand(Item item)
{
    if (item == null)
        return;

    SelectedItem = null;

    await Application.Current.MainPage.DisplayAlert("Selected", item.Text, "OK");
}