Oh, what a title for a post. The correct title is “‘A device attached to the system is not functioning. (Exception from HRESULT: 0x8007001F)’ Exception Occurs When Showing A TextBox and ApplicationLanguages.PrimaryLanguageOverride Is Set To An Invalid Value in Windows Store Apps on Windows 8.1“.
Symptom
Building the Factory Commander, I was using ApplicationLanguages.PrimaryLanguageOverride to set the culture-correct date and number formatting. This is how the implementation in App.OnLaunched looked like:
ApplicationLanguages.PrimaryLanguageOverride = new GeographicRegion().CodeTwoLetter;
Unfortunately, I can’t recall where I found this approach.
The development of Factory Commander was started on Windows 8, where this approach worked well. But after upgrading the development machine to Windows 8.1, the Commander crashed whenever I tried to rename, copy, or move a single item.
I figured out that, whenever the apps wants to show a TextBox, an exception with the description “A device attached to the system is not functioning. (Exception from HRESULT: 0x8007001F)” was thrown. The exception did not contain any further information. Well, what kind of device is used by a TextBox that is not used by other common controls of a Windows Store app?
A newly created Windows Store app on the same machine, which did contain a TextBox only, did not threw this exception. Was the Commander not compatible with Windows 8.1? I tested it on a machine having Windows 8.1 initially installed, so no upgrade was made: no problem! Did the upgrade corrupted the development machine?
Then I installed the Commander on a Windows RT device that was upgraded to Windows 8.1: no problem! Was it an issue with upgrading the x64 version of Windows 8? That seems to be the fact, because on another x64 machine that was upgraded to Windows 8.1, the same problem occurs. So I installed Windows 8 x64 on a new virtual machine, upgraded it to Windows 8.1: no problem.
The Reason
As you might assume from the description above, it took me some time to figure out what the cause was. The exception thrown was not really helpful – in other words: absolutely misleading – and the fact that the implementation worked fine on Windows 8, but partially did not on Windows 8.1, wasn’t helpful too. At least the “good” old step-by-step comparison approach made it.
Looking at the docs, ApplicationLanguages.PrimaryLanguageOverride expects a BCP-47 language tag. Valid values are for example “en”, “en-US”, “de”, “de-DE”, and so forth. The Commander set the value to GeographicRegion.CodeTwoLetter, which “… returns the two-letter ISO 3166-1 alpha-2 code for this region“.
If you are lucky, the region’s ISO code will match to the (or at least one) BCP-47 language code. In case you have the region set to “United States” (search for “region and language”), you do not have luck. The return value of GeographicRegion.CodeTwoLetter is “US”, which does not seem to be a valid BCP-47 code.
The Solution
I completely removed the setting of ApplicationLanguages.PrimaryLanguageOverride. The docs mention that “the … setting is persisted between sessions“. Means, the app needs to be uninstalled to have the change take effect.
To format the date and number values according to the user’s regional settings, I am using the CultureInfo of the user’s first configured language now. I was not able to figure out how to get the date and time formatting settings from the system.
// Get all installed languages
IReadOnlyList<string> languages
= Windows.System.UserProfile.GlobalizationPreferences.Languages;
// In case we have at least one, set the culture info from it.
// The result will be used later on as parameter
// of String.Format calls.
CultureInfo = languages.Count > 0
? new CultureInfo(languages[0])
: CultureInfo.DefaultThreadCurrentUICulture;
I think there should be one language defined at minimum, but who knows what might happen.
Advertisement Side Effects
A side effect of the change was that the Microsoft advertising services started to deliver ads. Before the change, I was wondering why the fill rate (quota number of items delivered by number of requests) was exactly zero. I.e. no ad was delivered at all.
After the change, ads were retrieved. This means that the app’s primary language is used to request ads in the matching language. And having an invalid language set, there will be no advertisement.
Expected Behavior
Letting the user of an API set invalid values without giving any feedback is not really helpful from my point of view.
What I expect from ApplicationLanguages.PrimaryLanguageOverride is to throw an ArgumentOutOfRangeException in case I try to set an invalid value. This would have saved me a lot of time.
It throws an ArgumentException telling the value does not fall within the expected range when I try to set it to a value like “abcd”. But as long as the format of the value matches to the BCP-47 language tag structure, like “ab” or “ab-cd”, no exception is thrown by the setter.
Try It Yourself
Are you curious and want to try it yourself? This is how I was able to reproduce the behavior:
-
Use Windows 8.1
Create a Blank Windows Store App, name it as you like (e.g. PrimaryLanguageOverrideTest)
Add
ApplicationLanguages.PrimaryLanguageOverride = "US"; as the first line of App.OnLaunched
Insert <TextBox> into the Grid of MainPage.xaml
Start the app in debug mode (press F5)
This will cause the app to crash with the exception described above.
To make the positive test, follow these steps:
-
Uninstall the app (search for it, right-click, choose uninstall)
Change
ApplicationLanguages.PrimaryLanguageOverride = "US"; to ApplicationLanguages.PrimaryLanguageOverride = "en-US";
Start the app in debug mode (press F5)
The app should start now without any problems.
Links
ApplicationLanguages.PrimaryLanguageOverride
BCP-47 language tag