CanExecute in MvvmCross

Question

I am working on a Xamarin.Android application and I am using MvvmCross. Here in my code DecreaseCommand is not working:

public class CartItemViewModel : MvxNotifyPropertyChanged
{      
    private int quantity = 0;      

    public CartItemViewModel()
    {
        IncreaseCommand = new MvxCommand(ExecuteIncreaseCommand, CanExecuteIncreaseCommand);
        DecreaseCommand = new MvxCommand(ExecuteDecreaseCommand, CanExecuteDecreaseCommand);
        Delete = new MvxCommand (() => {Quantity++;});
    }        

    public int Quantity
    {
        get { return quantity; }
        set
        {
            quantity = value;
            RaisePropertyChanged("Quantity");
            RaisePropertyChanged("SubTotal");
        }
    }

    public ICommand IncreaseCommand { get; set; }
    public ICommand DecreaseCommand { get; set; }
    public ICommand Delete { get; set; }


    private void ExecuteIncreaseCommand()
    {
         Quantity++;
    }

    private bool CanExecuteIncreaseCommand()
    {
        return true;
    }

    private void ExecuteDecreaseCommand()
    {
        Quantity--;
    }

    private bool CanExecuteDecreaseCommand()
    {
        return Quantity > 0;
    }


}

I suspect that CanExecuteDecreaseCommand is not firing, what could be wrong in this code?

Answer 1

You forgot to call RaiseCanExecuteChanged when you update your Quantity property.

Plus, you don't need to set a CanExecute that always returns true:

public class CartItemViewModel : MvxNotifyPropertyChanged
{      
    private int quantity = 0;      

    public CartItemViewModel()
    {
        IncreaseCommand = new MvxCommand(ExecuteIncreaseCommand);
        DecreaseCommand = new MvxCommand(ExecuteDecreaseCommand, CanExecuteDecreaseCommand);
        Delete = new MvxCommand (() => {Quantity++;});
    }        

    public int Quantity
    {
        get { return quantity; }
        set
        {
            quantity = value;
            RaisePropertyChanged("Quantity");
            RaisePropertyChanged("SubTotal");
            DecreaseCommand.RaiseCanExecuteChanged();
        }
    }

    public IMvxCommand IncreaseCommand { get; set; }
    public IMvxCommand DecreaseCommand { get; set; }
    public IMvxCommand Delete { get; set; }


    private void ExecuteIncreaseCommand()
    {
         Quantity++;
    }

    private void ExecuteDecreaseCommand()
    {
        Quantity--;
    }

    private bool CanExecuteDecreaseCommand()
    {
        return Quantity > 0;
    }
}