Hi is there a way to observe a MutableState value Like execu

Question

Hi is there a way to observe a MutableState value Like executing a code when the value is changed

SrSouza · Answer

You mean outside of a composition

Adam Powell · Answer

yes there are ways to do it that s how composition and compose ui do it slightly smiling face the best way to do it will depend on what the use case is What are you trying to do

Ayfri · Answer

I have 2 values the first is a string and the second is a value from an Enum The second is changed through a DropDown menu and I want the first to be equal to the name of the second But the first will later be used for multiple enums with other values like the second I have a main DropDown menu which presents you other DropDowns that will all set my first value

Ayfri · Answer

So I want to observe my second value to set the first value

Adam Powell · Answer

how is the first value currently represented

Adam Powell · Answer

It sounds like the first value is always a function of the second e g ```val first String get = second name```

hfhbd · Answer

Or use `derivedState` But a regular extension method sounds simpler

Adam Powell · Answer

yeah `derivedStateOf` is a good choice if the calculation is expensive and the result should be cached if not just make it a function that calculates the result based on the input states

Adam Powell · Answer

this is a kind of key element of declarative thinking with snapshots and compose instead of thinking in terms of observe changes in value A and update value B accordingly think in terms of B is defined as `f A `

Adam Powell · Answer

by thinking this way you leave no room for error no complexity of correct subscription management

Adam Powell · Answer

everything is defined in terms of single sources of truth for each input instead of as data processing pipelines with discrete imperative stages and update events

Ayfri · Answer

I can t use your solution Adam because I will maybe have other values that sets the first one My application is for creating JSON from templates but there are types of JSONs and type of these types like `Recipe` type and `Texture` type and for recipes there is `CraftingShapedRecipeTemplate` and `CraftingShapelessRecipeTemplate ` and `SmeltingRecipeTemplate ` etc same for `Texture` there are multiple types But I have 1 box that contains the fields the user have to complete for the template like `name` `id` etc there are a lot of different fields through the templates So to know what template I have I have multiple Enums like `RecipeType` and `TextureType` and for each enum I have a function `toTemplate ` which transform itself into the template So for now when my second value changes I set the first one to the Enum name and in the box I get back the template by searching through all the Enum if in any I can find a Enum value matching using `MyEnum values find it name == firstValue MyOtherEnum Values find it name == firstValue etc` and then I execute ` toTemplate ` or I return if null I don t know if it is a good architecture but I thought of this

Adam Powell · Answer

yeah I would probably find another way to do that slightly smiling face Even using an `Any` and a `when value is EnumTypeOne gt ` would be better than going through strings

Adam Powell · Answer

but the general declarative principle will still guide you to a simpler design that will have fewer opportunities for bugs `first` is equal to and then whatever logic is involved in determining its value absent any element of time or events

Ayfri · Answer

Okay I m gonna use the `when is ` so