Reading at navigation documentation

Question

Reading at navigation documentation <https developer android com jetpack compose navigation nav with args> I ve seen that we can navigate with string argument But is there a way to pass custom argument Or must I serialize deserialize between my custom `class` and `String` Or is even this last very bad practice

Leo Zam · Answer

We just convert object to json and wrap to base64 i guess it s only way

loloof64 · Answer

Thank you slightly smiling face I am also thinking about handling the data directly in the main activity where I define the ` Composable` so to do state hoisting I think i can handle that way also

loloof64 · Answer

This way

Colton Idle · Answer

It s a bad practice to pass anything but strings You should think of it like a web address You want to give an id in the web address not the full object serialized into a string From the docs gt Caution Passing complex data structures over arguments is considered an anti pattern Each destination should be responsible for loading UI data based on the minimum necessary information such as item IDs This simplifies process recreation and avoids potential data inconsistencies tldr Just use identifiers Bonus being you can retrieve stuff after process death if you really want to share an object just put the object in some shared scope by the two things that need it

Ian Lake · Answer

Yep identifiers make sense Arguments shouldn t be the source of truth for data

Ian Lake · Answer

That being said Navigation supports passing custom types if your identifier is complicated you absolutely shouldn t be base64ing anything <https developer android com guide navigation navigation kotlin dsl custom types|https developer android com guide navigation navigation kotlin dsl custom types>

loloof64 · Answer

< Colton Idle> Thank you I was not aware of this fact In fact I need to pass a list of PGNGame which is a custom type itself

loloof64 · Answer

< Ian Lake> Thank you So I ll need to review Jetpack Compose concepts as I m still having some issue understanding the fact that argument should not be the source of truth for data Also my PGNGame custom data is quite a rather complex data hold a mutable map from String to String and a list of another custom data

loloof64 · Answer

< Colton Idle> I will also investigate into the sharing solution from the top `Composable` in main activity

loloof64 · Answer

As my shared data is very very complex with a recursive data I went into sharing it with a view model Not sure if this is fine Also I m afraid this could create Memory Leak

loloof64 · Answer

Is there a better way to share complex recursive data among NavHost components

Colton Idle · Answer

I think its fine yeah lol

Colton Idle · Answer

you just gotta make sure you can get that data back if it goes away process death

loloof64 · Answer

No other way = gt so I m gonna for it

loloof64 · Answer

I m sure I can always recover data as in fact it is made from a Chess Pgn file format either from assets or from local files So all I have to do is to parse the file again and it s quite fast using an ANTLR4 grammar So yes data can be easily recovered

loloof64 · Answer

Finally came to make my custom data ` Parcelize` and to use this feature ```val games = extractGames fileData = it context = context navController currentBackStackEntry savedStateHandle set NavHostParcelizeArgs gamesList games navController navigate NavHostRoutes gamePage ``` and ```val gamesList = navController previousBackStackEntry savedStateHandle get lt List lt PGNGame gt gt NavHostParcelizeArgs gamesList ``` and ``` Composable fun MainContent stockfishLib StockfishLib val navController = rememberNavController NavHost navController startDestination = NavHostRoutes gamesListPage composable NavHostRoutes gamesListPage GamesListPage navController = navController composable NavHostRoutes gamePage GamePage navController = navController stockfishLib = stockfishLib ``` This way should be far cleaner

Ian Lake · Answer

No you really really don t want to be abusing savedStateHandle for that This is way way worse than your initial code of having a `rememberSaveable` above the NavHost layer acting as a repository that both destinations use as their source of truth

Ian Lake · Answer

I d suggest reading the Guide to App Architecture which talks specifically about how to get data onto your screens <https developer android com jetpack guide|https developer android com jetpack guide>

loloof64 · Answer

Hi eveyone I ve started to design my app with Jetpack Architecture components But then I m stuck about how to use my UseCase so that all screens can make a call to it More in the following posts

loloof64 · Answer

This is the use case

loloof64 · Answer

This is the data source

loloof64 · Answer

This is the repository

loloof64 · Answer

But how to share the use case to all screens I mean where should I instantiate it In the ` composable` which defines the `NavHost` And how to pass it to all screens In short where should I create the single instance of `GamesFromFileExtractorUseCase` Otherwise should the `GamesFromFileExtractorUseCase` be a Singleton object class

loloof64 · Answer

This is the current state of my main activity

loloof64 · Answer

Hi Is creating a Singleton of my use case this way fine Or is it bad practise Trying to follow Android Architecture Guidelines

Javier · Answer

I wouldn t use a `object` + `lateinit var` if I could use a `class` + ` Singleton` + `val`

loloof64 · Answer

Thank you ~~Could you give a simple snippet as an example Because I don t see yet how to apply your suggestion~~

loloof64 · Answer

Oups Didn t realize that ` Singleton` is also a Dagger annotation Thank you very much slightly smiling face

loloof64 · Answer

Meanwhile it seems that using ` Singleton` does not make it a Singleton <https stackoverflow com a 44237507 662618>

loloof64 · Answer

So maybe I should create it inside Application class instead <https stackoverflow com a 57118576 662618>

Javier · Answer

depending on how you configure ` Singleton` you should get the same instance always which is your use case

Javier · Answer

loloof64 · Answer

Thank you So I ll try this way Also the SO link I gave above was posted on 2019

loloof64 · Answer

I m still wondering if the following use of use case is good to set my main use case instance inside the application class and reference to it in each page

loloof64 · Answer

Here I m calling ``` context applicationContext as MyApplication gamesFromFileExtractorUseCase extractGame ``` but I m wondering whether it is better or worse than setting it inside NavHost state