Dark Mode for Xamarin Apps

This week I have mostly been trying to get Dark Mode working with one of my Xamarin Forms Shell apps. This is the new feature available on most mobile OSs where the screen goes white on black (rather then black on white) to reduce glare at night. There is no “out the box” solution but after much googling and a bit of fiddling I found something that works.

There were three main changes I had to make to get it working.

  1. Modify the Shell part of the app.
  2. Modify the content of the various ContentPages.
  3. Modify the splash screen.

Starting with points 1 & 2, I referred to these two posts for their approach. Read them but bear in mind I had the following issues. The general idea is that you have two resource dictionaries, one for the light screen and one for the dark screen. The elements have the same names so you can swap them over at run time and it applies the new colours to the existing controls.

Shell & ContentPages

I am quite new to using StaticResources. Hot Reload is great as you can edit the XAML and see it update on the device. This light/dark approach means that the resources are compiled and switched at runtime. This means Hot Reload doesn’t work as the XAML doesn’t have a direct “live” link to the app. This just means you have to get it all looking nice with the XAML as part of the app or page and then copy it to the light/dark ResourceDictionary when you have finished. You might also want to separate out and DataTemplates into another ResourceDictionary that uses the other two.

I also found that this process didn’t work for the Shell objects themselves. by that I mean the UI that presents itself when the app starts up. Navigation bars and Tab bars, but not modal pages. In these cases I defined the Shell colours like this.

<Shell xmlns=""
        BackgroundColor="{AppThemeBinding Light=SteelBlue, Dark=Black}"
        ForegroundColor="{AppThemeBinding Light=White, Dark=White}"
        TitleColor="{AppThemeBinding Light=White, Dark=White}"
        DisabledColor="{AppThemeBinding Light=Green, Dark=Green}"
        UnselectedColor="{AppThemeBinding Light=LightGray, Dark=DarkGray}"
        FlyoutBackgroundColor="{AppThemeBinding Light=White, Dark={OnPlatform Gray, iOS=Gray, Android=LightGray, UWP=Gray}}"

While in the content pages definitions it was used as

<Style TargetType="NavigationPage">
    <Setter Property="BarBackgroundColor" Value="{StaticResource NavigationPrimary}" />
    <Setter Property="BarTextColor" Value="White" />
    <Setter Property="BackgroundColor" Value="{StaticResource BackgroundColor}" />

Also occasionally I needed a DynamicResource instead of a static one. Half a template would update and half wouldn’t. Also it pays to check ALL of your screens work.

Splash Screens

These aren’t essential but are nice to have. Especially if your existing splash screen is light and bright. For this I mainly used this blog post as a reference. It explains everything you need to know , but as I had done a splashscreen before this was fairly familiar. The only thing I had trouble with was editing the iOS storyboard. I ended up adding the ViewController in XCode rather than in Visual Studio.


WiFi Android Debugging

I have a Galaxy S9. It works but the USB-C connector is a bit loose. I have had it replaced once and do most of my charging via a mat. However I still need the connector for deploying and debugging apps.

Well, it turns out you can deploy and debug via wifi. It is dead slow but it works. I got most of the details form here and here. Once you have your batch file correct, you run it and your phone magically appears as a launch option in Visual Studio.

First get the IP address of your phone from

Setting->Connections->Wifi->Current Network->Settings

and your device name from the Stack Overflow link. In my case I had emulators running as well as my phone so it is easier just to hardcode the command to work on your phone. Put the following into a batch file and change 227bef7922047ece to your device name and to your phones IP address.

@echo off
echo starting
echo Android bits
cd C:\Program Files (x86)\Android\android-sdk\platform-tools
adb -s 227bef7922047ece tcpip 5555
adb -s 227bef7922047ece connect
echo Finished

Then connect your phone via USB, run the batch file, unplug the USB and check Visual Studio. As I said earlier, it is dead slow but you can do most of your debugging in the emoulator and just deploy the odd build this way.

More detail here.