What's the difference between 'window' and 'screen' in the Dimensions API

Question

The documentation on Dimensions is quite poor (outstanding issue), so you'll have to dive into the code to understand what is going on. If you look at the source of Dimensions, you'll see this comment on line 47:

// Screen and window dimensions are different on android

If you trace back the history using blame, you'll find this commit on the relevant section of code pointing to this old issue which itself points to this issue about Dimensions reporting different screen heights.

I don't know enough about Android itself, but from what I can gather, it appears that Android can report back two different numbers:

1. width/height with soft menu bar
2. width/height without soft menu bar (so the actual entire screen)

A quick test on my Android device printing out these values and I was able to confirm that window's height < screen's height. So in all likelihood, this means:

• window: reports width/height without the soft menu bar
• screen: reports entire screen's width/height

I didn't follow back this product pain about orientation changes on Android, so I don't know how rotating your screen affects this.

On Android, window reflects the section of the total screen made available for this app. In most cases, width and height for window will be the same size or smaller than screen.

There are at least 3 cases where screen and window may be different:

1. If an Android device has the device navigation bar visible, the window height will be lower than screen height by the height of the navigator. This is illustrated in this answer by RY Zheng which was linked to in an answer to this question which got deleted.

   _{Example image of an Android system navigation bar from developer.android.com:}

2. If the app is shown in Android's split screen/multi-window mode, with windows for two apps side by side, window width or height will be lower than for screen based on how much of the width or height is given to that screen. This would have been documented by this PR by ThisIsMissEm, but it was closed by Facebook because no-one from Facebook got around to reviewing it.

   _{Example illustration of Android multi-window mode from developer.android.com:}

   

3. If an Android device had "screen zoom" or "display size" setting changed in Accessibility settings while the app was open, the scale, width and height properties for window will update to reflect the zoom but the properties for screen will not. If the app is restarted, the window scale property will match that of the screen.

   If an element with fixed dimensions fails to scale on changing screen zoom without restarting the app, multiplying those dimensions by Dimensions.get('window').scale / Dimensions.get('screen').scale may help.

   _{Example image of the Display Size accessibility settings UI from androidpolice.com:}

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So, width and height for window are usually the same size, or, sometimes on Android, smaller than screen.

There's only one exception I'm aware of where window may give values larger than screen: if the app was opened with "display size" or "screen zoom" accessibility setting set high, then, this was set lower with the app still open. In this case the height and width will be greater and the scale will be lower by the same ratio. I suspect this may be a bug in React Native rather than an intended behaviour and may change in a future release.