带有匿名方法的BackgroundWorker？

Question

我将使用匿名方法创建一个 BackgroundWorker。
我编写了以下代码：

BackgroundWorker bgw = new BackgroundWorker();
bgw.DoWork += new DoWorkEventHandler(
    () =>
    {
        int i = 0;
        foreach (var item in query2)
        {
            ....
            ....
        }
    }
);

但是委托“System.ComponentModel.DoWorkEventHandler”不接受“0”参数并且我有将两个对象传递给匿名方法：对象发送者，DoWorkEventArgs e

您能否指导我，我该怎么做？ 谢谢。

Answer 1

您只需要向匿名函数添加参数：

bgw.DoWork += (sender, e) => { ... }

或者如果您不关心参数，您可以：

bgw.DoWork += delegate { ... }

Answer 2

如果指定 lambda，则必须确保它采用相同数量的参数：

bgw.DoWork += (s, e) => ...;

但如果不使用参数，则可以仅使用不带参数的匿名委托：

bgw.DoWork += delegate
{
    ...
};

Answer 3

如果你在没有 lambda 的情况下编写了上面的内容，那会怎么样？

backgroundWorker1.DoWork += 
                new DoWorkEventHandler(backgroundWorker1_DoWork);

和命名方法：

private void backgroundWorker1_DoWork(object sender, 
        DoWorkEventArgs e)
    {   
        // Get the BackgroundWorker that raised this event.
        BackgroundWorker worker = sender as BackgroundWorker;

        // Assign the result of the computation
        // to the Result property of the DoWorkEventArgs
        // object. This is will be available to the 
        // RunWorkerCompleted eventhandler.
        e.Result = ComputeFibonacci((int)e.Argument, worker, e);
    }

但现在您使用的是没有绑定变量的 lambda ()=>;
您应该提供两个对象 sender 和 e （稍后将推断它们的类型）。

backgroundWorker1.DoWork += (sender, e) => ...

Answer 4

让我们变得简单

Lambda 表达式对于使代码更短、更具可读性来说非常方便。然而，入门级程序员可能会发现它有点难以处理。应该了解三个独立的概念：匿名方法、委托和 lambda 表达式。每个问题的详细介绍超出了本答案的范围。我希望下面给出的代码示例能够帮助您快速了解可用的不同方法。

class TestBed
{
    BackgroundWorker bgw = new BackgroundWorker();
    void sample()
    {            
        //approach #1
        bgw.DoWork += new DoWorkEventHandler(bgw_DoWork);
        //DoWorkEventHandler is nothing but a readily available delegate written by smart Microsoft guys

        //approach #2, to make it a little shorter
        bgw.DoWork += (s,e) => 
        {
            //...
        };
        //this is called lambda expression (see the => symbol)

        //approach #3, if lambda scares you
        bgw.DoWork += delegate 
        { 
            //... (but you can't have parameters in this approach
        };

        //approach #4, have a helper method to prepare the background worker
        prepareBgw((s,e)=>
        {
            //...
        }
        );

        //approach #5, helper along with a simple delegate, but no params possible
        prepareBgw(delegate 
        {
            //...
        }
        );

        //approach #6, helper along with passing the methodname as a delegate
        prepareBgw(bgw_DoWork);

        //approach #7, helper method applied on approach #1
        prepareBgw(new DoWorkEventHandler(bgw_DoWork));

    }

    void bgw_DoWork(object sender, DoWorkEventArgs e)
    {
        //...
    }
    void prepareBgw(DoWorkEventHandler doWork)
    {
        bgw.DoWork+= doWork;
    }
}

请注意，在本例中我们使用的是“delegate”而不是“Delegate”（两者之间是有区别的）