c# - 为什么我可以使用 lambda 表达式代替回调委托(delegate)？

Question

我发现了一些新的 C# 语法，但不明白它的含义。下面是语法相关的代码:

1)

BeginInvoke(new Action(() =>
    {
        PopulateUI(ds);
    }));

2)

private void OnFormLoad() 
{ 
    ThreadPool.QueueUserWorkItem(() => GetSqlData()); 
}

new Action() 是什么意思，=> 符号是什么意思？

ThreadPool.QueueUserWorkItem 的语法是 ThreadPool.QueueUserWorkItem(new WaitCallback(PrintOut), "Hello"); 但是这里显示的是 ThreadPool.QueueUserWorkItem( () => GetSqlData());，那么它是如何工作的呢？为什么 WaitCallback 不见了？请详细说明。

非常感谢。

Answer 1

看看

Action Delegate

Encapsulates a method that has a single parameter and does not return a value. You can use the Action delegate to pass a method as a parameter without explicitly declaring a custom delegate.

和

和Lambda Expressions (C# Programming Guide)

A lambda expression is an anonymous function that can contain expressions and statements, and can be used to create delegates or expression tree types.

All lambda expressions use the lambda operator =>, which is read as "goes to". The left side of the lambda operator specifies the input parameters (if any) and the right side holds the expression or statement block. The lambda expression x => x * x is read "x goes to x times x."