可以在MvvmCross中執行

Question

我正在使用Xamarin.Android應用程序，並且正在使用MvvmCross。在這裏，在我的代碼DecreaseCommand不工作：

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; 
    } 


} 

我懷疑CanExecuteDecreaseCommand不點火，這可能是錯誤的代碼？

Answer 1

當您更新Quantity屬性時，您忘記了撥打RaiseCanExecuteChanged。

另外，你不需要設置CanExecute總是返回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; 
    } 
}