Android - How to detect if night mode is on when using AppCompatDelegate.MODE_NIGHT_AUTO

int nightModeFlags =
    getContext().getResources().getConfiguration().uiMode &
    Configuration.UI_MODE_NIGHT_MASK;
switch (nightModeFlags) {
    case Configuration.UI_MODE_NIGHT_YES:
         doStuff();
         break;

    case Configuration.UI_MODE_NIGHT_NO:
         doStuff();
         break;

    case Configuration.UI_MODE_NIGHT_UNDEFINED:
         doStuff();
         break;
}

If you are kotlin developer then you can use below code to judge dark mode.

when (context.resources?.configuration?.uiMode?.and(Configuration.UI_MODE_NIGHT_MASK)) {
    Configuration.UI_MODE_NIGHT_YES -> {}
    Configuration.UI_MODE_NIGHT_NO -> {}
    Configuration.UI_MODE_NIGHT_UNDEFINED -> {}
}

For more about dark theme mode

https://github.com/android/user-interface-samples/tree/main/DarkTheme

A very simple solution is to add a string resource like this.

res/values/strings.xml

<string name="mode">Day</string>

res/values-night/strings.xml

<string name="mode">Night</string>

And then wherever you need to check it:

if (resources.getString(R.string.mode) == "Day") {
    // Do Day stuff here
} else {
    // Do night stuff here
}

But you CAN NOT call this before super.onCreate() in an activity's life-cycle. It will always return "Day" before onCreate.

The bitwise operator in Java (which is used in @ephemient 's answer) is different in kotlin so the code might not be easily convertible for beginners. Here is the kotlin version just in case someone needs it:

    private fun isUsingNightModeResources(): Boolean {
        return when (resources.configuration.uiMode and 
Configuration.UI_MODE_NIGHT_MASK) {
            Configuration.UI_MODE_NIGHT_YES -> true
            Configuration.UI_MODE_NIGHT_NO -> false
            Configuration.UI_MODE_NIGHT_UNDEFINED -> false
            else -> false
    }
}

For Xamarin.Android

if (Build.VERSION.SdkInt >= BuildVersionCodes.Froyo)
{
    var uiModeFlags = Application.Context.Resources.Configuration.UiMode & UiMode.NightMask;
    switch (uiModeFlags)
    {
        case UiMode.NightYes:
            // dark mode
            break;
        case UiMode.NightNo:
            // default mode
            break;
        default:
            // default mode
            break;
    }
}
else
{
// default mode
}