Converting dp to px without Context

Question

There is a very neat way of converting dp to px without Context, and it goes like this:

public static int dpToPx(int dp) {
    float density = Resources.getSystem().getDisplayMetrics().density;
    return Math.round((float) dp * density);
}

In every Google's example on Google GitHub page they are using the following approach:

public static int convertDpToPixel(Context ctx, int dp) {
    float density = ctx.getResources().getDisplayMetrics().density;
    return Math.round((float) dp * density);
}

So is there something wrong with the first approach? For me it works fine in all my apps, but I want to know is there some case where it might fail?

Answer 1

is there some case where it might fail?

Yes, there is!

Android supports different screens, for example you might cast the app with Chromecast or connect to a different screen by other means. In that case the values will not be converted properly to that other screen.

From the documentation for Resources.getSystem():

Return a global shared Resources object that provides access to only system resources (no application resources), and is not configured for the current screen (can not use dimension units, does not change based on orientation, etc).

Answer 2

Here is a little Kotlin extension function for that:

private fun Context.dpToPx(dp: Float): Float {
    val density = this.resources.displayMetrics.density
    return (dp * density).roundToInt().toFloat()
}