问题描述
取方法System.Windows.Forms.Control.Invoke（代表法）
Take the method System.Windows.Forms.Control.Invoke(Delegate method)
为什么这给一个编译时错误：
Why does this give a compile time error:
string str = "woop";
Invoke(() => this.Text = str);
// Error: Cannot convert lambda expression to type 'System.Delegate'
// because it is not a delegate type
然而，这工作得很好：
Yet this works fine:
string str = "woop";
Invoke((Action)(() => this.Text = str));
在该方法需要一个普通的代表？
When the method expects a plain Delegate?
推荐答案
一个拉姆达前pression既可以转换为委托类型或一个前pression树 - 但它必须知道的这的委托类型。只要知道签名是不够的。举例来说，假设我有：
A lambda expression can either be converted to a delegate type or an expression tree - but it has to know which delegate type. Just knowing the signature isn't enough. For instance, suppose I have:
public delegate void Action1();
public delegate void Action2();
...
Delegate x = () => Console.WriteLine("hi");
你所期望的对象的具体类型由 X 提及的是什么？是的，编译器的可能的产生具有适当签名的新的委托类型，但这是很少有用和你结束了错误检查少的机会。
What would you expect the concrete type of the object referred to by x to be? Yes, the compiler could generate a new delegate type with an appropriate signature, but that's rarely useful and you end up with less opportunity for error checking.
如果你想很容易地调用 Control.Invoke 与动作最容易做的事情是添加扩展的方法来控制：
If you want to make it easy to call Control.Invoke with an Action the easiest thing to do is add an extension method to Control:
public static void Invoke(this Control control, Action action)
{
control.Invoke((Delegate) action);
}
这篇关于为什么一定要当一个普通的委托参数提供一个lambda前pression定投的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！