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));  
}

which version of the .NET framework are you using? Is it Compact Framework? — Mitch Wheat, Sep 23 '09 at 23:51
@Dave Rook: To indent code in a list, you need to indent each line by 8 spaces. It's a Markdown quirk. See http://meta.stackexchange.com/questions/3792/how-to-nest-code-within-a-list-using-markdown — BoltClock, Jan 21 '14 at 10:17
@Dave Rook: You edited this post and raised it to our attention a couple of weeks ago (which was how I was able to ping you). A bit of a delay there but I thought I'd let you know regardless. — BoltClock, Jan 21 '14 at 10:37

score 44 · Answer 1 · answered Sep 23 '09 at 12:40

44

This works just fine;

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

By the way; I notice you mistyped the expression new uri(..., with lowercase uri. This is not your problem, is it? Because it should be "new Uri".

answered Sep 23 '09 at 12:40

Digitalex

1,494
9
11

No there are no typos in my code just in the typing here. Also the URl is dynamically generated at runtime. – dezkev Sep 23 '09 at 13:19

score 8 · Answer 2 · answered Apr 27 '10 at 10:26

Okay, so I think if the others have proved your URI is valid in their code and it compiles etc. and you also mention it is generated at runtime - it could be that the UriString you are generating at runtime is invalid and not what you are expecting?

Instead of letting an exception be thrown for attempting to create a Uri from an invalid string, I would suggest the following method IsWellFormedUriString on the Uri class.

string uriString = "your_UriString_here";

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

Might help with your debugging also.

score 5 · Answer 3 · answered Sep 23 '09 at 12:29

5

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

answered Sep 23 '09 at 12:29

Thomas Levesque

286,951
70
623
758

Thanks. Tried that too ( sorry did not mention above) - no dice. Compile error. – dezkev Sep 23 '09 at 12:30
Thie error could be due to the typo in things I have tried (b). We just can't tell. – spender Sep 23 '09 at 12:34

Daniel Elliott · Answer 4 · 2009-09-23T13:31:23.390

5

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

edited Sep 23 '09 at 13:31

answered Sep 23 '09 at 12:30

Daniel Elliott

22,647
10
64
82

Sorry Does'nt work; Now the error is as follows: Cannot resolve constructor: Memory Stream(void) candidates are: MemoryStream (byte[]) (in class memory stream) memoryStream (int) (in class memory stream) – dezkev Sep 23 '09 at 12:55
public void DownloadDataAsync(System.Uri address) Member of System.Net.WebClient Summary: Downloads the specified resource as a System.Byte array. This method does not block the calling thread. Parameters: address: A System.Uri containing the URI to download. – dezkev Sep 23 '09 at 13:20

score 0 · Answer 5 · answered Sep 23 '09 at 12:31

0

If I understand your code correctly, then

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

should work.

answered Sep 23 '09 at 12:31

Mitch Wheat

295,962
43
465
541

Yes, I want to use the Async method but I cannot because of the string to Uri thingy. The method above works fine. – dezkev Sep 23 '09 at 12:37

Cannot Convert System.String to System.Uri

5 Answers5

Linked