混乱`Action`委托和lambda表达式 [英] Confusion over `Action` delegate and lambda expressions

问题描述

private void StringAction(string aString) // method to be called
{
    return;
}

private void TestDelegateStatement1() // doesn't work
{
    var stringAction = new System.Action(StringAction("a string"));
    // Error: "Method expected"
}

private void TestDelegateStatement2() // doesn't work
{
    var stringAction = new System.Action(param => StringAction("a string"));
    // Error: "System.Argument doesn't take 1 arguments"

    stringAction();
}

private void TestDelegateStatement3() // this is ok
{
    var stringAction = new System.Action(StringActionCaller);

    stringAction();
}

private void StringActionCaller()
{
    StringAction("a string");
}

我不明白为什么 TestDelegateStatement3 的作品，但 TestDelegateStatement1 失败。在这两种情况下，动作与该接受零参数的方法提供。他们可能的呼叫的是只有一个参数（ ASTRING ），但应该是不相干的方法。他们不采取一个参数。这是不可能的做LAMDA表达式，还是我做错了什么？

I don't understand why TestDelegateStatement3 works but TestDelegateStatement1 fails. In both cases, Action is supplied with a method that takes zero parameters. They may call a method that takes a single parameter (aString), but that should be irrelevant. They don't take a parameter. Is this just not possible to do with lamda expressions, or am I doing something wrong?

推荐答案

正如你所说，行动没有按' t拍摄任何参数。
。如果你这样做：

As you said, Action doesn't take any parameters. If you do this:

var stringAction = new System.Action(StringAction("a string"));

您居然在这里执行的方法，所以这不是一个方法的参数。

You actually execute the method here, so that is not a method parameter.

如果你这样做：

var stringAction = new System.Action(param => StringAction("a string"));

你告诉它，你的方法接受一个名为参数参数，其操作不会

因此，要做到这一点，正确的方法是：

So the correct way to do this would be:

var stringAction = new System.Action( () => StringAction("a string"));

或更紧凑的：

Action stringAction = () => StringAction("a string");

空括号是用来标明拉姆达不带任何参数。

the empty brackets are used to indicate the lambda doesn't take any parameters.

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