在表达式主体成员中传递参数

问题描述 投票：0回答：1

我正在编写一个接收参数的 RelayCommand，但在调用实现该命令的方法时遇到问题。

我有以下 RelayCommand 类：

using System.Windows.Input;

namespace RCadastral.MVVM
{
    public class RelayCommand : ICommand
    {
        private Action<object> execute;
        private Func<object, bool> canExecute;

        public event EventHandler? CanExecuteChanged
        {
            add { CommandManager.RequerySuggested += value; }
            remove { CommandManager.RequerySuggested -= value; }
        }

        public RelayCommand(Action<object> execute, Func<object, bool> canExecute = null)
        {
            this.execute = execute;
            this.canExecute = canExecute;
        }

        public bool CanExecute(object? parameter)
        {
            return canExecute == null || canExecute(parameter);
        }

        public void Execute(object? parameter)
        {
            execute(parameter);
        }
    }
}

我认为我有以下几点：

<Window x:Class="RCadastral.View.DetalhePassoModalWindow"
        x:Name="DetalhePassoMW"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:RCadastral.View">

<Button x:Name="Back" 
        Content="Voltar" 
        Command="{Binding CloseCommand}"
        CommandParameter="{Binding ElementName=DetalhePassoMW}"/>
</Window>

在五月视图模式中我有以下内容：

public RelayCommand CloseCommand => new RelayCommand(execute => Close());
private void Close(Window window)
{
    // Sime logic...
    window.Close();
}

如何将参数传递给 Close() 方法？

我真的很困惑，没有任何效果。请帮忙。

c# wpf relaycommand
1个回答
0
投票

所以基本上，你做的一切都是正确的。在这段代码中

public RelayCommand CloseCommand => new RelayCommand(execute => Close());

private void Close(Window window)
{
    // Sime logic...
    window.Close();
}
您从 XAML 中使用

Window

 作为命令参数传递的
ElementName
 对象将是您用作命令操作的匿名函数中的
execute
 变量。

所以你能做的就是将其转换为正确的类型，然后执行你的逻辑：

public RelayCommand CloseCommand => new RelayCommand(execute => Close(execute as Window)); 
但是您也可以采用我的 
ICommand
 接口实现，它允许您使用带有通用参数的命令和更方便的方式来编写代码。


这是：


using System.Windows.Input;

namespace Wpf.Mvvm.Actions;

/// <summary>
/// Common <see cref="ICommand"/> implementation.
/// </summary>
/// <remarks>
/// Initializes a new instance of the <see cref="Command"/> class.
/// </remarks>
/// <param name="action">
/// Command action.
/// </param>
/// <param name="predicate">
/// Command predicate.
/// </param>
public sealed class Command(Action<object?> action, Func<object?, bool>? predicate) : ICommand
{
    #region Fields
    private readonly Func<object?, bool> _predicate = predicate ?? SuppressPredicate;
    #endregion

    #region Constructors
    /// <summary>
    /// Initializes a new instance of the <see cref="Command"/> class.
    /// </summary>
    /// <param name="action">
    /// Command action.
    /// </param>
    /// <param name="predicate">
    /// Command predicate.
    /// </param>
    public Command(Action<object?> action, Func<bool>? predicate)
        : this(action, predicate is null ? null : p => predicate()) { }

    /// <summary>
    /// Initializes a new instance of the <see cref="Command"/> class.
    /// </summary>
    /// <param name="action">
    /// Command action.
    /// </param>
    /// <param name="predicate">
    /// Command predicate.
    /// </param>
    public Command(Action action, Func<object?, bool>? predicate)
        : this(a => action(), predicate) { }

    /// <summary>
    /// Initializes a new instance of the <see cref="Command"/> class.
    /// </summary>
    /// <param name="action">
    /// Command action.
    /// </param>
    /// <param name="predicate">
    /// Command predicate.
    /// </param>
    public Command(Action action, Func<bool>? predicate)
        : this(a => action(), predicate is null ? null : p => predicate()) { }

    /// <summary>
    /// Initializes a new instance of the <see cref="Command"/> class.
    /// </summary>
    /// <param name="action">
    /// Command action.
    /// </param>
    public Command(Action<object?> action)
        : this(action, null as Func<object?, bool>) { }

    /// <summary>
    /// Initializes a new instance of the <see cref="Command"/> class.
    /// </summary>
    /// <param name="action">
    /// Command action.
    /// </param>
    public Command(Action action)
        : this(a => action(), null as Func<object?, bool>) { }
    #endregion

    #region Public methods
    /// <inheritdoc/>
    public bool CanExecute(object? parameter)
        => _predicate(parameter);

    /// <inheritdoc/>
    public void Execute(object? parameter)
        => action(parameter);
    #endregion

    #region Private methods
    /// <summary>
    /// Predicate suppression.
    /// <para>
    /// Used when constructor input predicate is <see langword="null"/>.
    /// </para>
    /// </summary>
    /// <param name="parameter">
    /// Predicate parameter.
    /// </param>
    /// <returns>
    /// Always returns <see langword="true"/>, meaning if
    /// <see langword="null"/> was passed into the command constructor
    /// - it will always be eligible for execution.
    /// </returns>
    private static bool SuppressPredicate(object? parameter)
        => true;
    #endregion

    #region Events
    /// <inheritdoc/>
    public event EventHandler? CanExecuteChanged
    {
        add => CommandManager.RequerySuggested += value;
        remove => CommandManager.RequerySuggested -= value;
    }
    #endregion
}

/// <summary>
/// Parametrized <see cref="ICommand"/> implementation.
/// </summary>
public sealed class Command<T>(Action<T?> action, Func<T?, bool>? predicate) : ICommand
{
    #region Fields
    private readonly Func<T?, bool> _predicate = predicate ?? SuppressPredicate;
    #endregion

    #region Constructors
    /// <summary>
    /// Initializes a new instance of the <see cref="Command"/> class.
    /// </summary>
    /// <param name="action">
    /// Command action.
    /// </param>
    /// <param name="predicate">
    /// Command predicate.
    /// </param>
    public Command(Action<T?> action, Func<bool>? predicate)
        : this(action, predicate is null ? null : p => predicate()) { }

    /// <summary>
    /// Initializes a new instance of the <see cref="Command"/> class.
    /// </summary>
    /// <param name="action">
    /// Command action.
    /// </param>
    public Command(Action<T?> action)
        : this(action, null as Func<T?, bool>) { }
    #endregion

    #region Public methods
    /// <inheritdoc/>
    public bool CanExecute(object? parameter)
        => _predicate((T?)parameter);

    /// <inheritdoc/>
    public void Execute(object? parameter)
        => action((T?)parameter);
    #endregion

    #region Private methods
    /// <summary>
    /// Predicate suppression.
    /// <para>
    /// Used when constructor input predicate is <see langword="null"/>.
    /// </para>
    /// </summary>
    /// <param name="parameter">
    /// Predicate parameter.
    /// </param>
    /// <returns>
    /// Always returns <see langword="true"/>, meaning if
    /// <see langword="null"/> was passed into the command constructor
    /// - it will always be eligible for execution.
    /// </returns>
    private static bool SuppressPredicate(T? parameter)
        => true;
    #endregion

    #region Events
    /// <inheritdoc/>
    public event EventHandler? CanExecuteChanged
    {
        add => CommandManager.RequerySuggested += value;
        remove => CommandManager.RequerySuggested -= value;
    }
    #endregion
}

因此，最终您的代码将如下所示：


public Command<Window> CloseCommand => new(Close);

private void Close(Window window)
{
    // Some logic...
    window.Close();
}

注意：我的代码利用了最新的 C# 功能之一 - 主构造函数，如果您使用的是较旧的语言版本，您可以手动恢复该用法。


希望这有帮助！

    

	

    

    


  

  

    
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