That s quite disappointing is there anything I can do to mak

Question

That s quite disappointing is there anything I can do to make Compose aware of the inside of an object

Mark Murphy · Answer

You could make `CalculatorState` be a `data class` with `val` properties then use `copy ` to create the mutated object that you use to update `calculatorState` Or you could have the individual properties of `CalculatorState` be `mutableStateOf ` property delegates Those correspond to alternatives 1 and 2 for the replacement of ` Model` as noted in this Gerrit entry <https android review googlesource com c platform frameworks support + 1311293 >

Adam Powell · Answer

Yep this is the way to do it

Adam Powell · Answer

I would strongly suggest going all the way for whichever approach you pick though if you choose the immutable state object held in a `MutableState lt CalculatorState gt ` great but if you make `CalculatorState` mutable by way of `mutableStateOf` property delegation don t use `State lt CalculatorState gt ` to hold it

Adam Powell · Answer

for all of the same reasons you would do `var list List lt T gt ` or `val list MutableList lt T gt ` but not `var list MutableList lt T gt `

Adam Powell · Answer

have either the object or the reference to that object be mutable but not both

galex · Answer

Thank you both really Interesting If the object is mine and I call it SomethingState I would expect Compose to be aware of it so I will use `mutableStateOf ` for its properties Using `copy` feels less clean memory wise but a good option if the object is not mine ex 3rd library

Adam Powell · Answer

Sounds like a good plan but the memory story isn t necessarily cut and dry `mutableStateOf` creates a mutable box and it does so with generics so anything you put in it is boxed as well We may do some additional optimizations around that last part later We also track historical values of `MutableState` objects to some extent in the form of the snapshot records Consider the API ergonomics you re trying to create here first and please report back if you experience issues and we ll see what we can do to optimize

Adam Powell · Answer

You re also very close to a pattern we like a lot for mutable hoisted state objects here if you go with that approach ``` Composable fun CalculatorScreen calculatorState CalculatorState = remember CalculatorState ```

Adam Powell · Answer

this lets your `CalculatorScreen` be self sufficient in the simple case but a caller that wants to also manipulate its `CalculatorState` via its public API can do so This is also great for testability since it means that `CalculatorScreen` itself is stateless and you can pass it any configuration you like to control and test its behavior

Adam Powell · Answer

it also means that by definition your `CalculatorState` object becomes a lot more testable so you can decouple testing of your logic in `CalculatorState` from testing the UI presentation itself

galex · Answer

That s just amazing I will use `remember` I haven t gotten to testing yet but it seems a thousand years easier than with the old UI framework

galex · Answer

I see in JetNews that s the pattern used indeed I didn t understand the reason for all those `mutableStateOf` but now it makes sense slightly smiling face

galex · Answer

Hey < Adam Powell> I tried to use `CalculatorState` in a junit simple test not AndroidTest and could not ```java lang IllegalStateException Not in a frame at androidx compose frames FramesKt currentFrame Frames kt 180 at androidx compose FramedMutableState setValue MutableState kt 296 at il co galex alexpizzapp feature calculator CalculatorState setNumberOfBalls CalculatorState kt 14 at il co galex alexpizzapp feature calculator CalculatorTest fourPizzasOf280 CalculatorTest kt 22 at sun reflect NativeMethodAccessorImpl invoke0 Native Method at sun reflect NativeMethodAccessorImpl invoke NativeMethodAccessorImpl java 62 at sun reflect DelegatingMethodAccessorImpl invoke DelegatingMethodAccessorImpl java 43 at java lang reflect Method invoke Method java 498 at org junit runners model FrameworkMethod$1 runReflectiveCall FrameworkMethod java 59 at org junit internal runners model ReflectiveCallable run ReflectiveCallable java 12 at org junit runners model FrameworkMethod invokeExplosively FrameworkMethod java 56 at org junit internal runners statements InvokeMethod evaluate InvokeMethod java 17 at org junit internal runners statements RunBefores evaluate RunBefores java 26 at org junit internal runners statements RunAfters evaluate RunAfters java 27 at org junit runners ParentRunner$3 evaluate ParentRunner java 306 at org junit runners BlockJUnit4ClassRunner$1 evaluate BlockJUnit4ClassRunner java 100 at org junit runners ParentRunner runLeaf ParentRunner java 366 at org junit runners BlockJUnit4ClassRunner runChild BlockJUnit4ClassRunner java 103 at org junit runners BlockJUnit4ClassRunner runChild BlockJUnit4ClassRunner java 63 at org junit runners ParentRunner$4 run ParentRunner java 331 at org junit runners ParentRunner$1 schedule ParentRunner java 79 at org junit runners ParentRunner runChildren ParentRunner java 329 at org junit runners ParentRunner access$100 ParentRunner java 66 at org junit runners ParentRunner$2 evaluate ParentRunner java 293 at org junit runners ParentRunner$3 evaluate ParentRunner java 306 at org junit runners ParentRunner run ParentRunner java 413 at org junit runner JUnitCore run JUnitCore java 137 at com intellij junit4 JUnit4IdeaTestRunner startRunnerWithArgs JUnit4IdeaTestRunner java 68 at com intellij rt junit IdeaTestRunner$Repeater startRunnerWithArgs IdeaTestRunner java 33 at com intellij rt junit JUnitStarter prepareStreamsAndStart JUnitStarter java 230 at com intellij rt junit JUnitStarter main JUnitStarter java 58 ``` So I am bound to test this code as an AndroidTest In this case a simpler object using `copy` would be easier to test right

Adam Powell · Answer

This might be a wait until Wednesday s dev15 release for the easiest fix in the form of the newer Snapshot replacement for Frames

Adam Powell · Answer

You can poke around a bit in the source tree for the parts to initialize frames outside of the usual Android setup harness if you want something sooner

galex · Answer

Ahaha I can wait till Wednesday smile Thanks