使用参数调用事件处理程序

Question

Visual Studio 2008，C# 3.0。

我有一个调用事件处理程序的方法。我想将该方法接收到的两个参数传递给事件处理程序。

我想做这样的事情：

wc.DownloadDataCompleted += wc.DownloadedDataCompleted(strtitle, placeid);

这是否可能，如果是，我将如何去做？

代码片段：

public void downloadphoto(string struri,string strtitle,string placeid)
{
    using (WebClient wc = new WebClient())
    {
        wc.DownloadDataCompleted += wc_DownloadDataCompleted;
        wc.DownloadDataAsync(new Uri(struri));
    }
}

Answer 1

DownloadDataAsync 有一个重载，它接受一个对象：

DownloadDataAsync(uri, object)

该对象可以是您想要传递到 DownloadDataCompleted 处理程序 中的任意对象：

public void downloadphoto(string struri,string strtitle,string placeid)
{
    using (WebClient wc = new WebClient())
    {
        string[] data = new string[2] { strtitle, placeid };
        wc.DownloadDataCompleted += wc_DownloadDataCompleted;
        wc.DownloadDataAsync(new Uri(struri), data);
    }
}


void wc_DownloadDataCompleted(object sender, DownloadDataCompletedEventArgs e)
{
    string[] data = (string[])e.UserToken;
    string strtitle = data[0];
    string placeid = data[1];
}

Answer 2

您可以创建一个私有类并将处理程序放在那里。例如

    public void downloadphoto(string struri, string strtitle, string placeid)
    {
        using (WebClient wc = new WebClient())
        {
            wcHandler handler = new wcHandler() { Strtitle = strtitle, Placeid = placeid };
            wc.DownloadDataCompleted += handler.wc_DownloadDataCompleted;
            wc.DownloadDataAsync(new Uri(struri));
        }

    }

    private class wcHandler
    {
        public string Strtitle { get; set; }
        public string Placeid { get; set; }

        public void wc_DownloadDataCompleted(object sender, DownloadDataCompletedEventArgs e)
        {
            // Do Stuff
        }
    }

，尽管如此，考虑到乔恩回答的优雅，可能会使用它！

Answer 3

Jon Skeet 已经回答了这个问题，展示了如何使用 lamda 表达式，但我仍然不清楚。我仍然需要更多示例，并最终使用按钮找到了这个简单的案例： http://social.msdn.microsoft.com/Forums/en-US/csharpgeneral/thread/74d03fe0-0fa5-438d-80e0-cf54fa15af0e

void A()  
{  
  Popup parameter = new Popup();  
  buttonClose.Click += (sender, e) => { buttonClose_Click(sender, e, parameter); };  
}  

static void buttonClose_Click(object sender, EventArgs e, Popup parameter)     
{     
  MakeSomethingWithPopupParameter(parameter);  
}

在我的案例中，我使用了 TreeView 控件的上下文菜单，最终看起来像这样：

private void TreeViewCreateContextMenu(TreeNode node)
{
    ContextMenuStrip contextMenu = new ContextMenuStrip();

    // create the menu items
    ToolStripMenuItem newMenuItem = new ToolStripMenuItem();
    newMenuItem.Text = "New...";

    // add the menu items to the menu
    contextMenu.Items.AddRange(new ToolStripMenuItem[] { newMenuItem });

    // add its event handler using a lambda expression, passing
    //  the additional parameter "myData"
    string myData = "This is the extra parameter.";
    newMenuItem.Click += (sender, e) => { newMenuItem_Click(sender, e, myData); };

    // finally, set the node's context menu
    node.ContextMenuStrip = contextMenu;
}

// the custom event handler, with "extraData":
private void newMenuItem_Click(object sender, EventArgs e, string extraData)
{
    // do something with "extraData"
}

Answer 4

最简单的方法是使用匿名函数（匿名方法或 lambda 表达式）来订阅事件，然后让您的方法仅包含您想要的参数：

public void downloadphoto(string struri, string strtitle, string placeid)
{
    using (WebClient wc = new WebClient())
    {
        wc.DownloadDataCompleted += (sender, args) => 
            DownloadDataCompleted(strtitle, placeid, args);
        wc.DownloadDataAsync(new Uri(struri));
    }
}

// Please rename the method to say what it does rather than where it's used :)
private void DownloadDataCompleted(string title, string id, 
                                   DownloadDataCompletedEventArgs args)
{
    // Do stuff here
}