UWP：RelayCommand 上的 Int 参数失败

Question

这段带有字符串参数的代码有效：

public RelayCommand<string> myCommand { get; private set; }
myCommand = new RelayCommand<string>((s) => Test(s));

private void Test(string s)
{
    //DoSomething();
}

此带有 int 参数的代码不起作用并给出 Compiler Error CS0452:

public RelayCommand<int> myCommand { get; private set; }
myCommand = new RelayCommand<int>((s) => Test(s));

private void Test(int s)
{
    //DoSomething();
}

RelayCommand Class 与 xaml 上的命令绑定 UI:

    public class RelayCommand<TParameter> : System.Windows.Input.ICommand
where TParameter : class
{
    protected readonly System.Func<TParameter, bool> _canExecute;
    private readonly System.Action<TParameter> _execute;
    public RelayCommand(System.Action<TParameter> execute)
    : this(execute, null)
    {
    }
    public RelayCommand(System.Action<TParameter> execute, System.Func<TParameter, bool> canExecute)
    {
        if (execute == null)
        { 
            throw new ArgumentNullException("execute");
        }
            
        _execute = execute;
        _canExecute = canExecute;
    }

    public bool CanExecute(object parameter)
    {
        return _canExecute == null ? true : _canExecute(parameter as TParameter);
    }
    public void Execute(object parameter)
    {
        _execute(parameter as TParameter);
    }
    public event EventHandler CanExecuteChanged;
    public void RaiseCanExecuteChanged()
    {
        System.EventHandler handler = CanExecuteChanged;
        if (handler != null)
        {
            handler(this, System.EventArgs.Empty);
        }
    }
}

除了将其转换为对象类型之外，还有其他想法吗？

Answer 1

如果您希望能够将 RelayCommand<TParameter> 实现与 int 等值类型一起使用，您需要删除类型约束并使用 as 运算符:

public class RelayCommand<TParameter> : System.Windows.Input.ICommand
{
    protected readonly System.Func<TParameter, bool> _canExecute;
    private readonly System.Action<TParameter> _execute;
    public RelayCommand(System.Action<TParameter> execute)
    : this(execute, null)
    {
    }
    public RelayCommand(System.Action<TParameter> execute, System.Func<TParameter, bool> canExecute)
    {
        if (execute == null)
        {
            throw new ArgumentNullException("execute");
        }

        _execute = execute;
        _canExecute = canExecute;
    }

    public bool CanExecute(object parameter)
    {
        if (_canExecute == null)
            return true;

        if (parameter is TParameter)
            return _canExecute((TParameter)parameter);

        return false;
    }
    public void Execute(object parameter)
    {
        if (parameter is TParameter)
            _execute((TParameter)parameter);
    }
    public event EventHandler CanExecuteChanged;
    public void RaiseCanExecuteChanged()
    {
        System.EventHandler handler = CanExecuteChanged;
        if (handler != null)
        {
            handler(this, System.EventArgs.Empty);
        }
    }
}

UWP：RelayCommand 上的 Int 参数失败

UWP: Int parameter fails on RelayCommand

c#

uwp

relaycommand

uno