我有这段代码:
WebClient webClient = new WebClient();
webClient.DownloadFileAsync(new Uri("http://MySite.com/Desktop/Pics.png"),
@"c:\users\Windows\desktop\DesktopsPics\Desktop.png");
我的程序会每天下载.png
张照片作为“每日照片”放在一个文件夹中!因此,当用户点击按钮时,如果服务器中已存在“每日图片”,则程序将下载此文件。
我可以使用上面的代码执行此操作,但是,如果服务器中尚不存在Pic.Png
,则我的程序会抛出错误。它会下载.html
文件,内容为404 not found
。
如果服务器上存在此文件,我该如何下载文件?
答案 0 :(得分:0)
由于您正在下载文件Async,因此需要在下载完成时添加事件处理程序。然后你可以检查arg是否有错误。
试试这个:
static void Main(string[] args)
{
WebClient client = new WebClient();
client.DownloadFileCompleted += new AsyncCompletedEventHandler(DownloadCompleted);
string fileName = Path.GetTempFileName();
client.DownloadFileAsync(new Uri("https://www.google.com/images/srpr/logo11w.png"), fileName, fileName);
Thread.Sleep(20000);
Console.WriteLine("Done");
}
private static void DownloadCompleted(object sender, AsyncCompletedEventArgs e)
{
if (e.Error != null)
{
// inspect error message for 404
Console.WriteLine(e.Error.Message);
if (e.Error.InnerException != null)
Console.WriteLine(e.Error.InnerException.Message);
}
else
{
// We have a file - do something with it
WebClient client = (WebClient)sender;
// display the response header so we can learn
foreach(string k in client.ResponseHeaders.AllKeys)
{
Console.Write(k);
Console.WriteLine(": {0}", client.ResponseHeaders[k]);
}
// since we know it's a png, let rename it
FileInfo temp = new FileInfo((string)e.UserState);
string pngFileName = Path.Combine(Path.GetTempPath(), "DesktopPhoto.png");
if (File.Exists(pngFileName))
File.Delete(pngFileName);
File.Move((string)e.UserState, pngFileName); // move to where ever you want
Process.Start(pngFileName);
}
}