I had been interested in making a part of my composable App

Question

I had been interested in making a part of my composable App keep the screen awake Reading though <https developer android com training scheduling wakelock kotlin|these docs> it shows that all the approaches include either an Activity or services etc has anyone had to do this before Any ideas on how to approach it

Stylianos Gakis · Answer

I was thinking of doing something like ``` Composable fun AwakeScreen content Composable gt Unit val window Window = null can I get access to the current window here Or some way to get the hosting activity which holds the window DisposableEffect Unit window addFlags WindowManager LayoutParams FLAG KEEP SCREEN ON onDispose window clearFlags WindowManager LayoutParams FLAG KEEP SCREEN ON content ``` But I am not sure we have access to this inside our composables Would I have to somehow hoist this all the way up to the hosting activity Anything smarter I should be able to do perhaps

Stylianos Gakis · Answer

Hmm this works actually ``` Composable fun AwakeScreen content Composable gt Unit val context = LocalContext current DisposableEffect Unit val powerManager = context getSystemService PowerManager class java val wakeLock = powerManager newWakeLock PowerManager SCREEN DIM WAKE LOCK myapp wakelock wakeLock acquire 10 minutes inWholeMilliseconds onDispose wakeLock release content ``` However `PowerManager SCREEN DIM WAKE LOCK` is deprecated suggesting to use the `FLAG KEEP SCREEN ON` on the window as I said before Can t find a way to do that so will use the deprecated option for now sweat smile

Albert Chang · Answer

You are abusing wake lock <https github com google accompanist blob main systemuicontroller src main java com google accompanist systemuicontroller SystemUiController kt L176|Here> s how you can access the window

Stylianos Gakis · Answer

This seems to work as well that s great ``` Composable fun AwakeScreen content Composable gt Unit val context = LocalContext current DisposableEffect Unit val window = context findWindow window addFlags WindowManager LayoutParams FLAG KEEP SCREEN ON onDispose window clearFlags WindowManager LayoutParams FLAG KEEP SCREEN ON content private fun Context findWindow Window var context = this while context is ContextWrapper if context is Activity return context window context = context baseContext return null ``` Now I gotta do a ` ` or at least a ` ` on the window though which either way doesn t make me feel that great I guess accessing it like this from a composable has no way of failing since it will always find the activity though right I d like to at least document that in that function if so so my colleagues don t need to worry about this not working

Stylianos Gakis · Answer

Also `LocalContext current findWindow ` and `LocalView current context findWindow ` should probably be equivalent since <https cs android com androidx platform frameworks support + androidx main compose ui ui src androidMain kotlin androidx compose ui platform AndroidCompositionLocals android kt l=89 q=AndroidCompositionLocals|this> is how they re provided so that s not important I assume

Albert Chang · Answer

Using `LocalView` in a library is safer as some people are overriding the context with their own ones e g to use a locale different from the default one

Stylianos Gakis · Answer

Right that s smart Thanks so much for saving me twice from doing something wrong joy hugging face

Adam Powell · Answer

you don t need the window for this since View has a keepScreenOn property of its own

Adam Powell · Answer

the view hierarchy automatically aggregates this within the window and handles it for you

Adam Powell · Answer

if you want to do this robustly from compose you ll want to refcount it so that multiple instances of something turning it on and off don t step on one another though

Adam Powell · Answer

something like this would do it untested code ```private val View keepScreenOnState KeepScreenOnState get = getTag R id keep screen on state as KeepScreenOnState KeepScreenOnState this also setTag R id keep screen on state it private class KeepScreenOnState private val view View private var refCount = 0 set value val newValue = value coerceAtLeast 0 field = newValue view keepScreenOn = newValue gt 0 fun request refCount++ fun release refCount Composable fun KeepScreenOnRequest val view = LocalView current DisposableEffect view val ksoState = view keepScreenOnState ksoState request onDispose ksoState release ``` and then declare the resource id `keep screen on state` in an `ids xml` resource file so that the `R` constant used above is there

Adam Powell · Answer

this approach maps to the `android keepScreenOn= true ` approach noted in the docs you linked above that s the view property mentioned

Stylianos Gakis · Answer

Oh alright didn t know keepScreenOn existed on the View itself as well Considering these two would be functionally equivalent this feels like a much more involved process and I d need to add this to my codebase probably with a link to this chat because otherwise whoever sees this would wonder why I didn t just do the normal approach If this is the way to do this in compose maybe it s worth a spot in the documentation

Adam Powell · Answer

probably worth adding the above to one of the official libraries really But there s nothing about it that isn t already documented in the link you posted

Stylianos Gakis · Answer

This would be perfect to exist in one of the official libraries indeed Thank you for your help

Dejan Predovic · Answer

``` Composable fun KeepScreenOn val activity = LocalContext current as Activity DisposableEffect Unit activity window addFlags WindowManager LayoutParams FLAG KEEP SCREEN ON onDispose activity window clearFlags WindowManager LayoutParams FLAG KEEP SCREEN ON ``` Works perfectly for me

Adam Powell · Answer

it will work in isolation only so long as there are either 0 or 1 of that composable present at a time Once there s more than one at a time for any reason and that can include things like animated transitions between screens then you can get into trouble if you re not scoping and reference counting it

Dejan Predovic · Answer

Hmmm You are right something like this should do the trick right

Dejan Predovic · Answer

```val keepScreenOnCounter = AtomicInteger 0 Composable fun KeepScreenOn val activity = LocalContext current as Activity DisposableEffect Unit val counter = keepScreenOnCounter incrementAndGet if counter == 1 activity window addFlags WindowManager LayoutParams FLAG KEEP SCREEN ON onDispose val counter = keepScreenOnCounter decrementAndGet if counter == 0 activity window clearFlags WindowManager LayoutParams FLAG KEEP SCREEN ON ```

Adam Powell · Answer

Nope because the activity window flags are per activity window and what you have there is global Plus if you have any other UI in the window it may also fight over the flag I m curious why not use what I pasted above That snippet will scope the changes to the ComposeView you re working with

Stylianos Gakis · Answer

Could this have been a Modifier btw I find it a bit awkward to have a random composable which doesn t emit any UI nor does it return a value so it s basically a side effect Maybe it s just because I am not used to doing something like this but anyway I ve looked into the Modifier documentation and I can t find too much about how to make our own one Not quite sure even if this use case fits a Modifier or how one would write one like that It s just that on the call site if I slapped a ` keepScreenOn` in the modifier chain of a composable I think it d feel more natural

Stylianos Gakis · Answer

Aha just this seems to work actually ```fun Modifier keepScreenOn = composed KeepScreenOnRequest this ``` Can anyone confirm that this is isn t fine Not sure if I am breaking some Modifier rule though sweat smile Can we just have whatever composables as part of a `composed` modifier Even ones that emit UI Is there some part of the documentation that talks more about all this and both don t mention this making me think this isn t what I want to do for some reason

Albert Chang · Answer

If it s a modifier what does it modify

Stylianos Gakis · Answer

It modifies its behavior on the screen and the flag of the current View it is inside isn t that a modification There are definitely modifiers that don t modify the composable size behavior itself like for example `onGloballyPositioned` or `onKeyEvent` which alters the keyboard behavior

Albert Chang · Answer

A modifier modifies the layout it s applied to It doesn t modify itself

Stylianos Gakis · Answer

Hmm yes that s true It just feels quite natural to be able to write `SomeComposable modifier = Modifier keepScreenOn ` as I feel like this is modifying my `SomeComposable` by making it keep the screen on just like I d expect all other modifiers to work Especially compared to having to put a `KeepScreenOnRequest ` at the top of a composable as a side effect at the spot I d also put a `SideEffect` or smth like that Maybe if I found a better name for it it d feel less weird

Stylianos Gakis · Answer

Maybe the best solution is for it to act like a wrapper like MaterialTheme does for example with a signature like ``` Composable fun ScreenOn content Composable gt Unit same code as Adam posted content ``` where I can add a `ScreenOn myComposables and just take the extra indentation

Albert Chang · Answer

It s basically the same as `BackHandler ` I think you just have to get used to it

Stylianos Gakis · Answer

TIL `BackHandler` exists And you re right it s the exact same approach Should probably just keep it like that then Thanks for helping me out on this one everyone