Question

Visual Studio 2008，C＃3.0。

下面有一个调用事件处理程序的方法。我想将方法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，如果是的话，我该怎么做呢？

代码段：

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

最简单的方法是使用匿名函数（匿名方法或lambda表达式）订阅事件，然后让你的方法只有你想要的参数：

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
}

Answer 2

DownloadDataAsync有一个带有对象的重载：

DownloadDataAsync(uri, object)

该对象可以是您希望传递到DownloadDataCompleted handler的任意内容：

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 3

您可以创建一个私有类并将处理程序放在那里。 E.g。

    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
        }
    }

虽然，鉴于Jon的答案的优雅可能会使用它！

Answer 4

Jon Skeet已经回答了这个问题，展示了如何使用lamda表达式，但我仍然不清楚它。我还需要更多示例，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); }

就我而言，我正在使用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" }

用参数调用eventhandler

4 个答案: