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#compose
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# compose
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Vinay Gaba
03/05/2021, 3:30 AMI’m curious about whether there is an API that allows me to get a callback about a composable being rendered on the screen or potentially modify a composable function right before its rendered. Sounds crazy I know but an API like
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Adam Powell
03/05/2021, 3:36 AMThe only real analog I can think of would be the composer interface itself. I'm curious what you would want to do along these lines
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Vinay Gaba
03/05/2021, 3:38 AMI was toying with the idea of adding overlays to composables for debugging reasons.
The simplest approach would be to create a default Modifier for your codebase that every Composable can use. The modifier would the provide this functionality through the logic that makes sense but I wonder if this can be done without every Composable having to “opt-in”
On a related note, I’m curious about what
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Zach Klippenstein (he/him) [MOD]
03/05/2021, 7:08 AMI would think you’d also need to get pretty granular events about individual recompose scopes – otherwise you’re analyzing the entire slot table/composable tree on every frame, which is quite slow (e.g. try clicking the checkbox in this sample app)
Hm, another idea: Can you wrap the
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Adam Powell
03/05/2021, 2:50 PMI think it's safe to say that this isn't a supported feature for the time being, but I'm keen to collect some use cases as it's kind of intriguing. We moved Composer to be an interface for other reasons of general API decoupling between the compiler plugin and runtime but it does raise this interesting avenue.
In general we've taken a fairly hard stance that thou shalt not manipulate the results of composable functions you call in any manner outside of their public API (which includes any CompositionLocals they consume)
This is demonstrated by the emit model, the preference for hoisted state objects as API, etc. Folks messing with Android date picker internals via findViewById and then being distressed by implementation detail changes that break those manipulations has stood as a cautionary tale throughout compose's development
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Vinay Gaba
03/05/2021, 4:44 PM@Zach Klippenstein (he/him) [MOD] Haven’t looked into hooks that UiApplier gives me but sounds like an interesting angle for sure!
@Adam Powell Thanks for shedding more light. I wonder how something like the overdraw debugging tool would be created in Compose? I know overdraw might not be that big of a concern in Compose due to the optimizations that are a first class citizen but a tool like that would be the use case that would require something like this.
the preference for hoisted state objects as APIOn a related note, I’m curious about how state hoisting relates to not allowing manipulation of composable functions?
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Adam Powell
03/05/2021, 4:56 PMonly in that it's a conscious pattern for exposing explicit API for callers to interact with
re. creating something like the overdraw debugging tool: probably by making it a part of compose-ui itself, from the state of things at the moment. Not a terribly satisfying answer, I know. 🙂
but for that in particular, drawing happens long after composition has come and gone. You would need to hook some very different parts of compose-ui than composition to do that.
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Vinay Gaba
03/05/2021, 5:09 PMwell I’m sure everything will be possible with time 😄 Doing this in compose-ui makes sense if I had some way to get this information. I have a couple crazy ideas to do it with what I have today but I don’t know if these would actually work.
1. Use the slot table to get the bounds of each composable in the hierarchy. Then create a separate Compose tree using these bounds with the information you want in the overlays of the Composable. Finally, wrap this overlay compose tree into a
ComposeViewComposeViewLayoutInflater.Factory2There are costs associated with both these options but since the purpose is debugging, maybe its acceptable to some level.
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Adam Powell
03/05/2021, 5:15 PMwhich overdraw debugging tool are you referring to anyway? the one in developer options already Just Works 🙂
(both 1 and 2 above are kind of terrifying)
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Vinay Gaba
03/05/2021, 6:04 PMhahaha agreed! And surprised to see the overdraw was just working but glad to see that! What I was hoping to do was something similar to overdraw where I add a colored overlay on top of the composable but also show the name of the composable in that overlay. This would help with something like component discovery.
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Adam Powell
03/05/2021, 7:01 PMyeah the layout inspector does the latter pretty well
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Zach Klippenstein (he/him) [MOD]
03/05/2021, 8:19 PMJust to ruin Adam’s day ( 😛 ), I prototyped my idea and it kinda works – although I did this during a meeting so i didn’t bother getting removals, moves, or size changes working, and those are the really interesting bits.
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Vinay Gaba
03/05/2021, 8:50 PMthat’s really cool!
and that’s a fair point. I just checked out the layout inspector with Compose support documentation and it seems like this should be good enough for now!
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