The Secret Diary of a Xamarin Android Developer, Aged 48 1/3


I have been trying to update Catfood Earth for Android to support Material You in Android 12. This sets a color palette from your wallpaper and other than making notifications harder to manage seems to be the main thing that Google has been working on for the past year. Live wallpaper isn't automatically supported, it's up to you to tell the system about your colors.

Happily there is an overridable OnComputeColors in WallpaperService.Engine, and you can create a WallpaperColors object from a bitmap so this looked like a five minute update. Hahahahahahhahahahah.

I spent a few weeks waiting for the Android 12 SDK to be available in Xamarin. I found some pointers to their GitHub and assumed it would show up there and so waited a few weeks. It still isn't there. I found some article about forcing it to install in Visual Studio 2019 that didn't work for me, and then realized that Visual Studio 2019 update checks were crashing. While trying to fix that I found that Visual Studio 2022 has been released and this installs with the Android 12 SDK!

These days I work on side projects when I get the occasional free hour. Almost inevitably that hour is consumed with updating two or three things and then hoping that the next time I get some time at least I'll be ready to go. But when that hour arrives I'm back to updating again.

So finally I have the right SDK and drop in an OnComputeColors and a call to NotifyColorsChanged when my wallpaper is updated. Time to start testing. The good news is that Material You is now working with Catfood Earth selected as the current wallpaper. The bad news is that every time I call NotifyColorsChanged the launcher disappears and I'm just left with the wallpaper and no icons or search box. Probably not a good experience. I try moving the NotifyColorsChanged call around to different points in code and it makes no difference. This simple update is rapidly spiraling from minutes to days to weeks.

Maybe it's some Xamarin bug, or something in Android 12 or maybe a change in the solemn contract between live wallpaper services and the rest of the system. Can't find any hint of any of this on the Internet.

It's also possible that the bitmap I'm passing is too large or too complex or too something else. So let's try just sending back a simple WallpaperColors in OnComputeColors and see if that helps.

The Android documentation for WallpaperColors suggests that you can construct it from three colors which seems sensible. The Xamarin implementation takes ColorObject instead of Color. What is a ColorObject? The sparse Xamarin documentation suggests that it has an empty constructor that creates an opaque black color and then properties like Red that are read only. So an immutable black? That can't be right? When constructing a color the constructor would seem like a great place to tell the class what color it is. Failing that, a FromColor or FromArgb would seem to follow the right sort of convention. But no. You need to find ValueOf. To create a color that is a class and not a value. Sigh. Maybe that is some kind of deep Android convention that I would just know if I did this more often than once a year or so.

Although, maybe most Google Developers can't figure out how to make a non-black color and that's the origin of Material Design 2. Everything else is just marketing rationalization on top of a terrible API.

Finally I have a simple WallpaperColors to test with but my build has broken. At some point while figuring out how to get a ColorObject that isn't black I thought a NuGet package would help. My project is now completely broken. My experience with touching NuGet is that you can either spend several days unpicking the carnage or just start over. Git reset --hard  HEAD it is then.

After quickly reimplementing the changes so far, returning a vanilla WallpaperColors object works... and so does the FromBitmap version. So 90% chance that I bodged something subtle the first time and didn't make the mistake on the second pass. 10% chance it was something strange in Visual Studio.

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I Thought He Came With You is Robert Ellison's blog.



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