如何将命令处理程序移动到另一个文件

Question

我从Microsoft Examples 中找到了一个自定义路由命令示例，它运行良好。

<Window x:Class="CustomRoutedCommand.MainWindow"
        ...
        xmlns:local="clr-namespace:CustomRoutedCommand">
    <Window.CommandBindings>
        <CommandBinding Command="{x:Static local:MainWindow.ColorCmd}"
                    Executed="ColorCmdExecuted"
                    CanExecute="ColorCmdCanExecute"/>
    </Window.CommandBindings>

void ColorCmdExecuted(object sender, ExecutedRoutedEventArgs e)、void ColorCmdCanExecute(object sender, CanExecuteRoutedEventArgs e) 在 MainWindow.cs 中定义。

如果我将这两个处理程序移动到 xxxx.cs，如何更改 XAML？

编辑，添加更多信息

命令处理程序在MainWindow.cs中定义，我将代码剪切并粘贴到另一个文件中，如下所示，然后编译出错。 错误 CS1061“MainWindow”不包含“ColorCmdExecuted”的定义

// xxxx.cs
namespace CustomRoutedCommand
{
    public class xxxx
    {
        // ExecutedRoutedEventHandler for the custom color command.
        private void ColorCmdExecuted(object sender, ExecutedRoutedEventArgs e)
        {
            var target = e.Source as Panel;
            if (target != null)
            {
                target.Background = target.Background == Brushes.AliceBlue ? Brushes.LemonChiffon : Brushes.AliceBlue;
            }
        }

        // CanExecuteRoutedEventHandler for the custom color command.
        private void ColorCmdCanExecute(object sender, CanExecuteRoutedEventArgs e)
        {
            if (e.Source is Panel)
            {
                e.CanExecute = true;
            }
            else
            {
                e.CanExecute = false;
            }
        }
    }
}

Answer 1

您不能将在 XAML 标记中挂钩的实际事件处理程序移动到另一个类，但您可以在另一个类中实现逻辑：

public partial class MainWindow : Window
{
    public static RoutedCommand ColorCmd = new RoutedCommand();

    public MainWindow()
    {
        InitializeComponent();
    }

    private void ColorCmdExecuted(object sender, ExecutedRoutedEventArgs e)
    {
        xxxx.ColorCmdExecuted(e.Source);
    }

    private void ColorCmdCanExecute(object sender, CanExecuteRoutedEventArgs e)
    {
        e.CanExecute = xxxx.ColorCmdCanExecute(e.Source);
    }
}

public class xxxx
{
    public static void ColorCmdExecuted(object parameter)
    {
        var target = parameter as Panel;
        if (target != null)
        {
            target.Background = target.Background == Brushes.AliceBlue ? Brushes.LemonChiffon : Brushes.AliceBlue;
        }
    }

    public static bool ColorCmdCanExecute(object parameter)
    {
        return parameter is Panel;
    }
}

您可能希望将RoutedCommand 替换为ICommand 接口的自定义实现，当您直接执行命令时可以执行一些操作：

public class RelayCommand : ICommand
{
    private Action<object> _execute;
    private Predicate<object> _canExecute;

    public RelayCommand(Action<object> execute, Predicate<object> canExecute)
    {
        _execute = execute;
        _canExecute = canExecute;
    }
    public event EventHandler CanExecuteChanged;

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

    public void Execute(object parameter)
    {
        if (_execute != null)
            _execute(parameter);
    }
}

public partial class MainWindow : Window
{
    public static RelayCommand ColorCmd = new RelayCommand(xxxx.ColorCmdExecuted, null);

    public MainWindow()
    {
        InitializeComponent();
    }
}

public class xxxx
{
    public static void ColorCmdExecuted(object parameter)
    {
        var target = parameter as Panel;
        if (target != null)
        {
            target.Background = target.Background == Brushes.AliceBlue ? Brushes.LemonChiffon : Brushes.AliceBlue;
        }
    }
}

XAML：

<Button Command="{x:Static local:MainWindow.ColorCmd}" Content="CommandTarget = FristStackPanel" />

有关此概念的更多信息，请参阅this 博客文章。

Answer 2

您可以继续使用static 命令，但更常见的是使用称为RelayCommand 的ICommand 实现。这使我们可以更轻松地利用 MVVM，以便您的视图模型模型可以处理命令。这是ICommand的基本示例实现：

public class RelayCommand : ICommand
{
    private Predicate<object> _canExecute;
    private Action<object> _execute;

    public RelayCommand(Predicate<object> canExecute, Action<object> execute)
    {
        _canExecute = canExecute;
        _execute = execute;
    }

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

    public bool CanExecute(object parameter)
    {
        return _canExecute(parameter);
    }

    public void Execute(object parameter)
    {
        _execute(parameter);
    }
}

然后，您可以将RelayCommand 作为属性添加到您的视图模型中，如下所示：

public class ViewModel : ViewModelBase
{
    private RelayCommand colorCmd;
    public ICommand ColorCmd
    {
        get
        {
            colorCmd ?? colorCmd = new RelayCommand(p => ColorCmdCanExecute(), p => ColorCmdExectued());
            return colorCmd;
        }
    }

    private bool ColorCmdCanExecute()
    {
        //CanExecute code here
        ...
    }

    private void ColorCmdExecuted()
    {
        //Command execute code here
        ...
    }
}

有关 MVVM 和ICommand 实现的更多信息，有很多资源。 This one 对于 WPF 初学者来说非常容易理解，并且应该让您对如何进行有更多的了解。