c# - 是否可以在匿名函数中设置 "this"？

Question

我有一个函数，

public SharpQuery Each(Action<int, HtmlNode> function)
{
    for (int i = 0; i < _context.Count; ++i)
        function(i, _context[i]);
    return this;
}

它为上下文的每个元素调用传入的函数。是否可以在 Action<int, HtmlNode> function 中设置“this”所指的内容？ ？

例如，

sharpQuery.Each((i, node) => /* `this` refers to an HtmlNode here */);

Answer 1

稍微改变一下功能，就可以达到想要的效果。

public SharpQuery Each(Action<MyObject, int, HtmlNode> function)
{
    for (int i = 0; i < _context.Count; ++i)
        function(this, i, _context[i]);
    return this;
}

然后你可以这样写你的函数调用:

sharpQuery.Each((self, i, node) => /* do something with `self` which is "this" */);

注意:匿名函数只能访问公共(public)成员。如果匿名函数是在类中定义的，它将像往常一样访问 protected 和私有(private)成员。

例如，

class MyObject
{
    public MyObject(int i)
    {
        this.Number = i;
    }

    public int Number { get; private set; }
    private int NumberPlus { get { return Number + 1; } }

    public void DoAction(Action<MyObject> action)
    {
        action(this);
    }

    public void PrintNumberPlus()
    {
        DoAction(self => Console.WriteLine(self.NumberPlus));  // has access to private `NumberPlus`
    }
}

MyObject obj = new MyObject(20);
obj.DoAction(self => Console.WriteLine(self.Number));     // ok
obj.PrintNumberPlus();                                    // ok
obj.DoAction(self => Console.WriteLine(self.NumberPlus)); // error