Xamarin.Forms ChangeCanExecute没有使用正确的参数

Question

I have a Xamarin.Forms application running in UWP where I use the DLToolkit.Forms.Controls.FlowListView (from daniel-luberda ) to display some kind of grid view with buttons.

The Mvvm framework used is FreshMvvm.

Here is my gridview in XAML:

<c:FlowListView SeparatorVisibility="None" 
    HasUnevenRows="False" FlowColumnMinWidth="100" 
    FlowItemsSource="{Binding Boards}">
    <c:FlowListView.FlowColumnTemplate>
        <DataTemplate>
            <Button  Text="{Binding Number}" 
                Command="{Binding Path=BindingContext.SelectBoardCommand, Source={x:Reference Name=SalesPage}}" 
                CommandParameter="{Binding .}" />
        </DataTemplate>
    </c:FlowListView.FlowColumnTemplate>
</c:FlowListView>

Here is the result (I simplified the XAML concerning color and size) :

The button inside my gridview is binded to a command with a parameter. Each time I click on a button, I would like to disable it.

And my command looks like this:

    private ICommand _selectBoardCommand;

    [DoNotNotify]
    public ICommand SelectBoardCommand => _selectBoardCommand = new Command<BoardModel>(board =>
    {
        board.NotUsed = false;
        ((Command<BoardModel>) _selectBoardCommand).ChangeCanExecute();
    }, board => board != null && board.NotUsed);

Pushing on a button calls the command with the right parameter (the board.Number binded to the text of the command is the one I get in the command). But when calling the "CanChangeExecute" in order to disable the command, I can't pass the selected board as argument.

And in the command, when using

((Command<BoardModel>) _selectBoardCommand).ChangeCanExecute();

it calls the Func

board => board != null && board.NotUsed

with the latest item of the list.

Moreover, I needed to put a "board != null" in the ChangeCanExecute because this Func is called a lot of time with null values.

Any idea?

Answer 1

I see two ways out of your problem:
1) Move SelectBoardCommand inside BoardModel . It won't need a parameter and will operate on each model individually;
2) Bind Enabled property of Button to NotUsed property. In this case, user won't be able to call SelectBoardCommand from UI at all.