Dark Mode Musings: Beware of the Context 🌗

Rebecca Franks — Sat, 14 Dec 2019 08:06:05 +0000

I’ve been working on getting Dark Mode in our app fully supported and I stumbled upon an interesting finding:

The Application#applicationContext does not keep information about the theme that you have set via AppCompatDelegate.setDefaultNightMode(), only a View or Activity context has this information stored.

After reading through Chris Banes’ articles and watching some great talks about Styles, Themes & Dark Mode, I felt pretty comfortable that I knew quite a bit about the Theming system on Android. However, this particular issue was something that I was not expecting, which is why I decided to document this particular problem I faced.

The Problem

I have the “Dark theme” set on in my system settings, but inside my app I am explicitly setting the theme to light mode (even though my device theme is set to Dark):

AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_NO)

I have two bitmap resources: one located in drawable and one located in drawable-night.

Despite my app theme overriding the mode to “light”, the resource from drawable-night was loaded instead of the one from the drawable folder.

Why was this happening? 🧐

I was using the Application#applicationContext to load up the Bitmap:

class BitmapLoader(val context: Context) {

    override fun loadBitmap(@RawRes resourceId: Int, bitmapConfig: Bitmap.Config): Bitmap? {
        val options =
            BitmapFactory.Options().apply { inPreferredConfig = bitmapConfig }
        return BitmapFactory.decodeResource(
            context.resources, resourceId, options
        )
    }
}
// This class was used in a similar way to the following usage:
val bitmapLoader = BitmapLoader(application.applicationContext)

The Solution

The fix in this case was to use the Activity#context method or View#context, instead of Application#applicationContext.

The lesson here is that the Application#applicationContext should not be used for retrieving UI resources. The Application object will only have system-level information and not information that is set by AppCompatDelegate. AppCompatDelegate only works on the activity-level.

You need to be very careful of the context you use when obtaining resources that could change based on the theme.

Thanks for reading, if you have any questions or comments — feel free to reach out on Twitter @riggaroo.

Thanks to Chris Banes and Alan Viverette for confirming what I was experiencing is intentional.

Nevertheless, Rebecca Franks Coded

Rebecca Franks — Tue, 07 Mar 2017 06:38:39 +0000

I began coding because...

I was curious. I wanted a job where I could combine maths and computers. I chose a degree that suited that without any knowledge of how to program. It was tough, I spent a lot more time than everyone else reading as much as I could in order to have it make sense to me. The first 6 months of university were the hardest, I couldn't cope as well as the others. I had countless thoughts of quitting but instead I kept at it until it made sense.

I'm currently hacking on...

Many things, mostly learning about Android Things and electronics. I'm a real electronics newbie, so I am learning a lot as I go and blogging about it on https://riggaroo.co.za.

I'm excited about...

The future of technology. I cant wait for driverless cars to become popular. I believe there is still so much to be discovered and made. I really want more innovations with the food industry to come about, things such as ovens that can bake things themselves and know when food is ready.

My advice for other women who code is...

It gets easier! Not easier as in "I understand everything about coding and I know it all", it gets easier as in "I don't know how to solve this problem but I am confident I can figure it out". The truth is you will never know everything there is to know, there will always be a new language, a new platform, a new templating engine. It is impossible to know everything. Most importantly just keep going. Make sure you learn a new skill everyday. Encourage others and never forget that once upon a time you also had no clue how to code.

DEV Community: Rebecca Franks