C# Loading images async

Question

the program i'm currently creating has some pictureboxes. The images from these are not added to the resources, instead i want to load them from a website. Its working fine so far, the biggest problem is that the program crashes if it could not load the images. I searched for this problem and it seems that getting the images async would be the right way to solve this problem.

Currently this is the way i'm loading the images:

private static Image GetImageFromURL(string url)
{
    HttpWebRequest httpWebRequest = (HttpWebRequest)HttpWebRequest.Create(url);
    HttpWebResponse httpWebReponse = (HttpWebResponse)httpWebRequest.GetResponse();
    Stream stream = httpWebReponse.GetResponseStream();
    return Image.FromStream(stream);
}

....

foo.Image = GetImageFromURL("https://foo.com/bar.jpg");

I've read many threads on SO and other sites but i still dont understand async. I realy hope someone here can try to explain how to use it if async is the right way to go.

Sorry for my bad english, i hope its not to hard to understand.

`"getting the images async would be the right way to solve this problem"` - What makes you think that? Determining *why* the application is failing seems like a good first step to preventing that from happening, rather than making random changes and hoping for the best. Otherwise the same problem will still manifest, just asynchronously. — David, May 03 '16 at 16:06
@David Its not that much about crashing itself. I maybe should have explained it a little bit better. The program is crashing if it cant find a working connection to get the images. This should be easy to fix. The async part is more to solve a long loading time while starting the program if the connection or the website is slow. — Backslash, May 03 '16 at 16:10
The `PictureBox` control has built-in support to load `Image` from a Url asynchronously. [Asynchronously Load an Image from a Url to a PictureBox](http://stackoverflow.com/questions/37763916/asynchronously-load-an-image-from-a-url-to-a-picturebox) — Reza Aghaei, Jul 12 '16 at 14:09

score 1 · Accepted Answer · answered May 03 '16 at 16:17

In general with the .NET built-in objects (and hopefully by convention with any objects), the "async" version is used by simply using the Async corresponding method.

For example, instead of this:

HttpWebResponse httpWebReponse = (HttpWebResponse)httpWebRequest.GetResponse();

You would have this:

HttpWebResponse httpWebReponse = (HttpWebResponse)(await httpWebRequest.GetResponseAsync());

Note the addition of the Async on the method call, found here, as well as the addition of the await keyword. This latter change would necessitate a change to the method signature as well:

private static async Task<Image> GetImageFromURL(string url)

And any method which invokes it would have to change as well:

Image someImage = await GetImageFromURL(someUrl);

The asynchronous operation should continue as such all the way to the top level. (The common way of saying this is that it should be "async all the way down".)

Once the method is async, you can have as many await operations within it as you like. Some of the other methods you're currently calling may also have Async equivalents, so you can do the same with them.

That makes everything a little bit more clear. To use await GetImageFromURL i need to have it in a async method, right? — Backslash, May 03 '16 at 16:35
@Backslash: Correct. The underlying asynchronous operations should be exposed all the way up to the application host level so it can handle them accordingly. Never "hide" an asynchronous operation behind a synchronous interface, that would open the door to all sorts of difficult-to-find bugs. — David, May 03 '16 at 16:41
Thank you, everything is working now and i think i understand the most of it! :) — Backslash, May 03 '16 at 18:14

C# Loading images async

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