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Question

我将使用匿名方法创建 BackgroundWorker 我写了以下代码：

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

但 委托'System.ComponentModel.DoWorkEventHandler'不接受'0'参数 ，我必须将两个对象传递给匿名方法：对象发送方，DoWorkEventArgs e

你能指导我，我该怎么办？感谢。

Answer 1

您只需要向匿名函数添加参数：

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

如果你不关心参数，你可以：

bgw.DoWork += delegate { ... }

Answer 2

如果指定lambda，则必须确保它具有相同数量的参数：

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

但是如果您没有使用参数，则可以使用不带参数的匿名委托：

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

Answer 3

如果你在没有lambdas的情况下写了上面的内容会怎么样？

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);
    }

但是现在你使用没有绑定变量的lambdas（）=＆gt; 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

让我们简单

Lambda表达式非常方便使代码更短，更易读。但入门级程序员可能会觉得处理起来有点困难。应该经历三个独立的概念：匿名方法，委托和lambda表达式。详细介绍每一项都超出了这个答案的范围。我希望下面给出的代码示例能够快速查看可用的不同方法。

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，我们在此示例中使用了“delegate”而不是“Delegate”（两者之间存在差异）

BackgroundWorker用匿名方法？

4 个答案:

让我们简单