ReactiveCommandとInt32のCanExecuteプロパティー

Question

私は次のviewmodelを持っています。私はSubmitOrderコマンドに対してcanSubmit observableを使用します。 QuantityプロパティはTextBoxのtextプロパティにバインドされます。そして、テキストボックスにテキストを入力すると、observable canSubmitトリガされず、コマンドが有効になります。

public class CreateOrderViewModel : ReactiveObject 
{ 
    private int _quantity; 
    public int Quantity 
    { 
     get { return _quantity; } 
     set { this.RaiseAndSetIfChanged(ref _quantity, value); } 
    } 

    private ISymbol _selectedSymbol; 

    public ISymbol SelectedSymbol 
    { 
     get { return _selectedSymbol; } 
     set { this.RaiseAndSetIfChanged(ref _selectedSymbol, value); } 
    } 

    private BuySell _side; 

    public BuySell Side 
    { 
     get { return _side; } 
     set { this.RaiseAndSetIfChanged(ref _side, value); } 
    } 

    public ReactiveCommand<Unit, IOrderProcessor> SubmitOrder { get; } 

    public CreateOrderViewModel(IOrderService orderService) 
    { 
     var canSubmit = this.WhenAnyValue(v => v.SelectedSymbol, v => v.Quantity, 
      (symbol, quantity) => symbol != null && quantity > 0); 

     SubmitOrder = ReactiveCommand.Create(
      () => orderService.SubmitOrder(CreateOrderFromParameters()), 
      canSubmit); 
    } 

    private Order CreateOrderFromParameters() 
    { 
     return new Order 
     { 
      Quantity = Quantity, 
      Symbol = SelectedSymbol, 
      Side = Side 
     }; 
    } 
} 

私のXAML：

<TextBlock Grid.Row="0" Grid.Column="0" 
      Text="{x:Static properties1:Resources.Quantity}" 
      /> 
<TextBox Grid.Row="0" Grid.Column="1" 
     Text="{Binding Quantity, UpdateSourceTrigger=PropertyChanged}" 
     /> 

<TextBlock Grid.Row="0" Grid.Column="2" 
      Text="{x:Static properties1:Resources.Symbol}" 
      /> 
<ComboBox Grid.Row="0" Grid.Column="3" 
      ItemsSource="{Binding Symbols}" 
      DisplayMemberPath="Ticker" 
      SelectedItem="{Binding SelectedSymbol}" 
      /> 

<StackPanel Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="6" 
      HorizontalAlignment="Left"> 
    <Button Content="{x:Static properties1:Resources.Submit}" 
      Command="{Binding SubmitOrder}" 
      /> 
</StackPanel>  

Answer 1

がStringToNullableNumericConverter使って、私の問題を解決：

public class StringToNullableNumberConverter : IValueConverter 
{ 
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture) 
    { 
     return value; 
    } 

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) 
    { 
     var stringValue = value as string; 

     if (stringValue == null) return value; 

     if (targetType == typeof(int?)) 
     { 
      int intValue; 
      if (Int32.TryParse(stringValue, out intValue)) 
      { 
       return intValue; 
      } 

      return null; 
     } 

     return value; 
    } 
} 

folowingのviewmodelで：

private int? _quantity; 
    public int? Quantity 
    { 
     get { return _quantity; } 
     set 
     { 
      if (!value.HasValue || value <= 0) 
      { 
       SetError(nameof(Quantity), Resources.Properties.Resources.OrderQuantityMustBePositiveErrorMessage); 
      } 
      else 
      { 
       ClearErrors(nameof(Quantity)); 
       this.RaiseAndSetIfChanged(ref _quantity, value); 
      } 
     } 
    }