DispatcherTimer和WebClient.DownloadStringAsync引发“ WebClient不支持并发I / O操作”异常

问题描述

| 我需要有关此代码的帮助

WebClient client = new WebClient();
    string url = \"http://someUrl.com\"

    dispatcherTimer timer = new dispatcherTimer();
                timer.Interval = TimeSpan.FromSeconds(Convert.Todouble(18.0));
                timer.Start();

                timer.Tick += new EventHandler(delegate(object p,EventArgs a)
                {
                     client.DownloadStringAsync(new Uri(url));

                     //throw:
                     //WebClient does not support concurrent I/O operations.
                });

                client.DownloadStringCompleted += (s,ea) =>
                {
                     //Do something
                };

    

解决方法

您正在使用共享的“ 1”实例，并且计时器显然导致一次进行多个下载。每次在

Tick

处理程序中启动一个新的客户端实例，或禁用计时器，以便在您仍在处理当前下载内容时不会再次打勾。

timer.Tick += new EventHandler(delegate(object p,EventArgs a)
{
    // Disable the timer so there won\'t be another tick causing an overlapped request
    timer.IsEnabled = false;

    client.DownloadStringAsync(new Uri(url));                     
});

client.DownloadStringCompleted += (s,ea) =>
{
    // Re-enable the timer
    timer.IsEnabled = true;

    //Do something                
};