A method was called at an unexpected time

Question

I'm trying to iterate all files in a directory using GetFilesAsync, but every time I call the GetResults method, it throws an exception that says

System.InvalidOperationException: A method was called at an unexpected time

The code is simply

var files = myStorageFolder.GetFilesAsync(); //runs fine
var results = files.GetResults(); //throws the exception

I'm new to Win 8 dev so I might be missing something obvious.

Edit (solved) I'm running my console application, but now that the program runs async, the files.GetResult() method no longer exists.

static void Main(string[] args)
{
   var files = GetFiles(myStorageFolder);
   var results = files.GetAwaiter().GetResults();//Need to add GetAwaiter()
}

static async Task GetFiles(StorageFolder sf)
{
   await sf.GetFilesAsync();
}

score 41 · Answer 1 · answered Sep 21 '13 at 16:23

41

If you don't want to use the asynckeyword (in my case, the code was inside a property, so asyncwasn't an option), you can use a TaskAwaiter instead, by chaining these two methods:

var folder = Package.Current.InstalledLocation.GetFolderAsync("folderName").GetAwaiter().GetResult();

This won't throw a InvalidOperationException nor cause a deadlock.

answered Sep 21 '13 at 16:23

dcastro

66,540
21
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1

Do I need any `Using` statements to use the `GetAwaiter` method? – JKennedy Nov 24 '16 at 09:45
1

@user1 I can't remember, this is from 2 years ago. But looking through the docs, this is the extension method you need: [`WindowsRuntimeSystemExtensions.GetAwaiter`](https://msdn.microsoft.com/en-us/library/hh582011(v=vs.110).aspx). It's defined in the `System` namespace, so you probably have it in scope already – dcastro Nov 24 '16 at 11:14
7

I noticed the `GetAwaiter()` was on a `Task` and I was trying to use it on an `IAwaitableOperation` so I had to call `AsTask` then `Results`, damn `UWP`. Thanks though! – JKennedy Nov 24 '16 at 11:17
This also solves the issue when in an `if` statement as well. I was receiving the error when I just ran the application, but not if I placed a breakpoint just before the `if` statement and used Step Into to run through the `if` statement. `if(ApplicationData.Current.LocalFolder.TryGetItemAsync("savedFavorites.xml").GetAwaiter().GetResult() == null)` – Keven M Mar 14 '19 at 16:15

score 13 · Accepted Answer · answered Oct 27 '12 at 01:31

13

You need to wait for the async method to complete. So you could use the new await as one option:

var files = await myStorageFolder.GetFilesAsync();

You might want to check the documentation on dealing with async methods here.

answered Oct 27 '12 at 01:31

AndrewS

6,054
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31

score 1 · Answer 3 · answered Oct 25 '20 at 22:02

1

If you are using an variation of Task like Windows.Foundation.IAsyncOperation the code can be like this:

var file = StorageFile.GetFileFromPathAsync(protocolArgs.Uri.LocalPath).AsTask().Result;

answered Oct 25 '20 at 22:02

Murilo Maciel Curti

2,677
1
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score 0 · Answer 4 · answered Oct 27 '12 at 01:31

you should await the var files = myStorageFolder.GetFilesAsync(); as the operation might still be running when you get to next instruction var results = files.GetResults(); //throws the exception

var files = await myStorageFolder.GetFilesAsync(); //runs fine
var results = files.GetResults(); //this will run when call above returns

A method was called at an unexpected time

4 Answers4

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