c# - Cannot Convert System.String to System.Uri

Question

I am using the Web Client Class to download files from the internet (Flickr actually). This works fine as long as I use : WebClient().DownloadData(string) , however this locks up the UI as it is Not asynchronous.

However when I try WebClient().DownloadDatAsync(string), I get a compile error: "Unable to convert System.String to System.Uri".

The string MediumUrl returns "http://farm4.static.flickr.com/2232/2232/someimage.jpg"

So the question is how do I convert the string "http://farm4.static.flickr.com/2232/2232/someimage.jpg" to a Uri.

Things I have tried-

I have tried to cast it to Uri but that does not work either.

I have tried Uri myuri = new uri(string) - errors out as above.

foreach (Photo photo in allphotos)  
{  
    //Console.WriteLine(String.Format("photo title is :{0}", photo.Title));
    objimage = new MemoryStream(wc.DownloadData(photo.MediumUrl));
    images.Add(new Pictures(new Bitmap(objimage), photo.MediumUrl, photo.Title));  
}

score 43 · Accepted Answer

这工作得很好；

System.Uri uri = new System.Uri("http://farm4.static.flickr.com/2232/2232/someimage.jpg");

顺便一提; 我注意到您输入错误的表达式 new uri(...，使用小写的 uri。这不是您的问题，是吗？因为它应该是“new Uri”。

score 8 · Accepted Answer

好的，所以我认为如果其他人已经证明您的 URI 在他们的代码中有效并且可以编译等，并且您还提到它是在运行时生成的 - 可能是您在运行时生成的 UriString 无效，而不是您是什么期待？

我建议不要在尝试从无效字符串创建 Uri 时引发异常，而是建议在Uri类上使用以下方法IsWellFormedUriString 。

string uriString = "your_UriString_here";

if (Uri.IsWellFormedUriString(uriString, UriKind.Absolute))
{
    Uri uri = new Uri(uriString);
}
else
{
    Logger.WriteEvent("invalid uriString: " + uriString);
}

也可能有助于您的调试。

score 5 · Accepted Answer

objimage = new MemoryStream(wc.DownloadData(new Uri(photo.MediumUrl)));

b) I have tried Uri myuri = new uri(string) - errors out as above.

This is the usual way to create a Uri from a string... I don't see why it wouldn't work if the string is a valid URI

score 5 · Accepted Answer

var yourUri = new UriBuilder(yourString).Uri;

So your example would be:

wc.DownloadDataAsync(new UriBuilder(photo.MediumUrl).Uri);
objimage = new MemoryStream(wc.Result);

You may need to put a check in to see the operation has completed.

Hope that helps,

Dan

score 0 · Accepted Answer

If I understand your code correctly, then

wc.DownloadDataAsync(new Uri(photo.MediumUrl));

should work.

c# - Cannot Convert System.String to System.Uri

5 回答 5

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