与这里使用的LINQ代码对应的事件处理程序是什么?

Question

我看过一些关于MVVW的教程，但我仍然不确定。

在这个网站。因此，我实现了它提供的方法:

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Input;
namespace OCLMEditor
{
    public class DelegateCommand<T> : System.Windows.Input.ICommand
    {
        private readonly Predicate<T> _canExecute;
        private readonly Action<T> _execute;
        public DelegateCommand(Action<T> execute)
            : this(execute, null)
        {
        }
        public DelegateCommand(Action<T> execute, Predicate<T> canExecute)
        {
            _execute = execute;
            _canExecute = canExecute;
        }
        public bool CanExecute(object parameter)
        {
            if (_canExecute == null)
                return true;
            return _canExecute((parameter == null) ? default(T) : (T)Convert.ChangeType(parameter, typeof(T)));
        }
        public void Execute(object parameter)
        {
            _execute((parameter == null) ? default(T) : (T)Convert.ChangeType(parameter, typeof(T)));
        }
        public event EventHandler CanExecuteChanged;
        public void RaiseCanExecuteChanged()
        {
            if (CanExecuteChanged != null)
                CanExecuteChanged(this, EventArgs.Empty);
        }
    }
}

现在，在我的ViewModel中我有这个:

public class OCLMEditorModelView
{
    private readonly DelegateCommand<string> _DeleteStudentButtonClickCommand;
    public ObservableCollection<Student> Students
    {
        get
        {
            return _Model.Students;
        }
    }
    private Student _SelectedStudentItem;
    public Student SelectedStudentItem
    {
        get { return _SelectedStudentItem; }
        set
        {
            _SelectedStudentItem = value;
            _DeleteStudentButtonClickCommand.RaiseCanExecuteChanged();
        }
    }
    private OCLMEditorModel _Model;
    public List<StudyPointItem> ReadingStudyPointsList { get; set; }
    public List<StudyPointItem> StudentStudyPointsList { get; set; }
    public List<String> TreasureItemMethodsList { get; set; }
    public OCLMEditorModelView()
    {
        InitTreasureItemMethodsList();
        InitReadingStudyPointsList();
        InitStudentStudyPointsList();
        _Model = new OCLMEditorModel();
        _DeleteStudentButtonClickCommand = new DelegateCommand<string>(
            (s) => { _Model.Students.Remove(_SelectedStudentItem); _Model.Serialize(); MessageBox.Show("Student deleted!"); }, //Execute
            (s) => { return _SelectedStudentItem != null; } //CanExecute
            );
    }
    public DelegateCommand<string> DeleteStudentButtonClickCommand
    {
        get { return _DeleteStudentButtonClickCommand; }
    }
    // Code snipped
}

为完整起见，按钮的XAML:

<Button x:Name="buttonDeleteStudent" 
        Content="Delete" 
        Margin="2" 
        Command="{Binding DeleteStudentButtonClickCommand}"/>

一切正常。但是我发现这段代码很难读(LINQ):

 _DeleteStudentButtonClickCommand = new DelegateCommand<string>(
    (s) => { _Model.Students.Remove(_SelectedStudentItem); _Model.Serialize(); MessageBox.Show("Student deleted!"); }, //Execute
    (s) => { return _SelectedStudentItem != null; } //CanExecute
    );

我知道它在干什么。但是，如果我的代码变得更复杂，我更喜欢一个专门的处理程序。如何定义这个处理程序?

谢谢。

Answer 1

澄清一下，这不是linq，它只是作为参数传递的lambda方法。

如果你想坚持使用DelegateCommand类，那么你可以定义方法，而不是通过替换:

public OCLMEditorModelView()
{
    InitTreasureItemMethodsList();
    InitReadingStudyPointsList();
    InitStudentStudyPointsList();
    _Model = new OCLMEditorModel();
    _DeleteStudentButtonClickCommand = new DelegateCommand<string>(
        (s) => { _Model.Students.Remove(_SelectedStudentItem); _Model.Serialize(); MessageBox.Show("Student deleted!"); }, //Execute
        (s) => { return _SelectedStudentItem != null; } //CanExecute
        );
}

public OCLMEditorModelView()
{
    InitTreasureItemMethodsList();
    InitReadingStudyPointsList();
    InitStudentStudyPointsList();
    _Model = new OCLMEditorModel();
    _DeleteStudentButtonClickCommand = new DelegateCommand<string>(
        ExecuteMethod, //Execute
        CanExecuteMethod//CanExecute
        );
}
void ExecuteMethod(string s)
{
    _Model.Students.Remove(_SelectedStudentItem); 
    _Model.Serialize(); 
    MessageBox.Show("Student deleted!"); 
}
bool CanExecuteMethod(string s)
{
    return _SelectedStudentItem != null;
}

请注意，这真的没有增加任何可维护性，相反，如果你在其他地方重用这些方法代码，这是一件好事，但是用匿名方法或lambda语法定义内联方法的目的是让代码显示在使用它的地方，这对于小的不可重用的代码片段来说是很好的。还要注意，在lambda语法版本中，CanExecute可以简化(单个语句，可以删除括号并返回)，并且没有理由将所有内容写在一行中(因此在Execute中每个语句可以在自己的行中)。我将把它重写为:

public OCLMEditorModelView()
{
InitTreasureItemMethodsList();
InitReadingStudyPointsList();
InitStudentStudyPointsList();
_Model = new OCLMEditorModel();
_DeleteStudentButtonClickCommand = new DelegateCommand<string>(
    (s) => 
        { 
            _Model.Students.Remove(_SelectedStudentItem); 
            _Model.Serialize(); 
            MessageBox.Show("Student deleted!"); 
        },
    (s) => _SelectedStudentItem != null);
}