有没有办法指定“空”C# lambda 表达式？

Is there a way to specify an "empty" C# lambda expression?

提问by Rob

I'd like to declare an "empty" lambda expression that does, well, nothing. Is there a way to do something like this without needing the DoNothing()method?

我想声明一个“空”的 lambda 表达式，它什么都不做。有没有办法在不需要方法的情况下做这样的事情DoNothing()？

public MyViewModel()
{
    SomeMenuCommand = new RelayCommand(
            x => DoNothing(),
            x => CanSomeMenuCommandExecute());
}

private void DoNothing()
{
}

private bool CanSomeMenuCommandExecute()
{
    // this depends on my mood
}

My intent in doing this is only control the enabled/disabled state of my WPF command, but that's an aside. Maybe it's just too early in the morning for me, but I imagine there must be a way to just declare the x => DoNothing()lambda expression in some way like this to accomplish the same thing:

我这样做的目的只是控制我的 WPF 命令的启用/禁用状态，但这是旁观。也许这对我来说太早了，但我想必须有一种方法可以x => DoNothing()像这样以某种方式声明lambda 表达式来完成同样的事情：

SomeMenuCommand = new RelayCommand(
    x => (),
    x => CanSomeMenuCommandExecute());

Is there some way to do this? It just seems unnecessary to need a do-nothing method.

有没有办法做到这一点？似乎没有必要采取什么都不做的方法。

采纳答案by Rauhotz

Action doNothing = () => { };

回答by Jon Skeet

Assuming you only need a delegate (rather than an expression tree) then this should work:

假设您只需要一个委托（而不是表达式树），那么这应该可以工作：

SomeMenuCommand = new RelayCommand(
        x => {},
        x => CanSomeMenuCommandExecute());

(That won't work with expression trees as it's got a statement body. See section 4.6 of the C# 3.0 spec for more details.)

（这不适用于表达式树，因为它有一个语句体。有关更多详细信息，请参阅 C# 3.0 规范的第 4.6 节。）

回答by Joseph

This should work:

这应该有效：

SomeMenuCommand = new RelayCommand(
    x => {},
    x => CanSomeMenuCommandExecute());

回答by Jorge Córdoba

I don't fully understand why do you need a DoNothing method.

我不完全明白为什么你需要一个 DoNothing 方法。

Can't you just do:

你不能只做：

SomeMenuCommand = new RelayCommand(
                null,
                x => CanSomeMenuCommandExecute());

回答by Anthony

This is an old question, but I thought I would add some code that I've found useful for this type of situation. I have an Actionsstatic class and a Functionsstatic class with some basic functions in them:

这是一个老问题，但我想我会添加一些我发现对这种情况有用的代码。我有一个Actions静态类和一个Functions静态类，其中包含一些基本功能：

public static class Actions
{
  public static void Empty() { }
  public static void Empty<T>(T value) { }
  public static void Empty<T1, T2>(T1 value1, T2 value2) { }
  /* Put as many overloads as you want */
}

public static class Functions
{
  public static T Identity<T>(T value) { return value; }

  public static T0 Default<T0>() { return default(T0); }
  public static T0 Default<T1, T0>(T1 value1) { return default(T0); }
  /* Put as many overloads as you want */

  /* Some other potential methods */
  public static bool IsNull<T>(T entity) where T : class { return entity == null; }
  public static bool IsNonNull<T>(T entity) where T : class { return entity != null; }

  /* Put as many overloads for True and False as you want */
  public static bool True<T>(T entity) { return true; }
  public static bool False<T>(T entity) { return false; }
}

I believe this helps improve readability just a tiny bit:

我相信这有助于提高可读性只是一点点：

SomeMenuCommand = new RelayCommand(
        Actions.Empty,
        x => CanSomeMenuCommandExecute());

// Another example:
var lOrderedStrings = GetCollectionOfStrings().OrderBy(Functions.Identity);