Curious question, do my Compose Functions finally use View.java to be rendered on the Screen, if not...

# compose

[Gaurav Gangwar]

Curious question, do my Compose Functions finally use View.java to be rendered on the Screen, if not then how does the final rendering happen ? If there is any good resource available on this, please point me to that.

[nitrog42]

it uses a ComposeView to be on the screen

[Filip Wiesner]

No, thankfully there is no View.java at the and 😌 But the final rendering is done using Skia just like the "old" system.
Sadly I don't know about some in-depth article about the rendering but hey, it's Google I/O tomorrow so there might be some talk about it.

[Gaurav Gangwar]

ComposeView extends ViewGroup ?

[nitrog42]

yes

[Gaurav Gangwar]

which inturn extends View.java

[nitrog42]

yes, I'm not sure they are any way around that because it still has to use the Activity "system" provided in every Android phones

[nitrog42]

but the use of the "View" part seems hollow, if we look at the code of a composeView, you will not see calls/redefined draw(), onDraw() , so for the rendering part I would follow what @Filip Wiesner said

[Filip Wiesner]

it uses a ComposeView to render on screen

I believe that ComposeView is just bridge to the View system and saying that it's used to render Composable functions is a little misleading. I haven't fact-checked this I think that there is no ComposeView if you directly use setContent { // compose } in your activity.
It's completely different drawing system based on Compose UI nodes and you can think of ComposeView as Canas of sorts. It's just a portal to a differrent world.

[nitrog42]

setContent in Activity does use a ComposeView, but you are right on the rest and I changed my wording

[nitrog42]

[Filip Wiesner]

Oh okay, my bad 🙂
To the original question, I think that Leland Richardson and Romain Guy talked a little bit about this process on the latest episode of Android Leaks podcast.

[Albert Chang]

For rendering, Compose UI uses RenderNode APIs on API 23+ and View APIs on API 21-22.

[Albert Chang]

If what you're asking is whether Compose UI reuses standard Android widgets, then the answer is no.

[Albert Chang]

You can see all the internals here.

[Gaurav Gangwar]

Thanks guys, will go through these.

[Adam Powell]

A View is the lowest level construct Android exposes for UI that interfaces with the system. An Android window is nothing more than a View added to the WindowManager. Compose represents your UI as the contents of a View and uses that View as an interface to the rest of Android.

[Filip Wiesner]

Hmmm, next time I'll rather keep my mouth shut when I am not 100% sure 😅 Sorry for the misinformation