Simple app to show different screens in Jetpack Compose and how to navigate between them.
This is part of the Jetpack Compose navigation series:
Part 1 - Simple Jetpack Compose Navigation Example
I created this simple app to try out the navigation component in Jetpack Compose. This is how the app looks like.
These are the steps to implement this simple app.
1. Add Navigation Compose Library
In app\build.gradle
, add this dependency.
dependencies {
implementation "androidx.navigation:navigation-compose:2.5.0-alpha01"
}
2. Create NavHostController
NavHostController
is required to build the navigation graph in the next step which is used to navigate to different screens.
Create this NavHostController
using rememberNavController()
in your root composable function and pass that into the NavGraph()
composable function.
@Composable
private fun MainScreen() {
SimpleNavComposeAppTheme {
val navController = rememberNavController()
NavGraph(navController)
}
}
3. Build Navigation Graph
The navigation graph looks like this:
- Login Screen -> Home Screen -> Profile Screen
- Login Screen -> Home Screen -> Search Screen
Login screen is the start destination. Home screen takes no navigation argument. Profile screen takes 2 navigation arguments and search screen takes 1 navigation argument.
To build the navigation graph, you use NavHost()
composable function and NavGraphBuilder.composable()
function to build each composable screen.
fun NavGraph(navController: NavHostController) {
NavHost(
navController = navController,
startDestination = "login"
) {
composable(route = "login") {
//call LoginScreen composable function here
}
composable(route = "home") {
//call HomeScreen composable function here
}
...
}
}
To navigate to home screen:
navController.navigate("home")
To pop back current stack:
navController.popBackStack()
To pop up to login screen:
navController.popBackStack(NavRoute.Login.path, inclusive = false)
Navigation With Arguments
navGraphBuilder.composable
has 2 parameters - route
and arguments
. To navigation with argument, we want to update both route
and arguments
parameters.
This is route format for profile screen. id
is the first parameter. showDetails
is the second parameter.
route = "profile/{id}/{showDetails}"
The arguments
parameter looks like this:
arguments = listOf(
navArgument("id") {
type = NavType.IntType
}
,
navArgument("showDetails") {
type = NavType.BoolType
}
)
You can specify the NavType
of the parameter. You can also set the defaultValue
to make the argument optional.
...
navArgument("showDetails") {
type = NavType.BoolType
defaultValue = false
}
...
I personally will avoid using
defautValue
because it requires your route to follow certain format (i.e."profile/{id}/?showDetails={showDetails}"
).?showDetails
is the optional arguement to allow you specify thedefaultValue
.
To retrieve the argument value, you use the NavBackStackEntry.arguments
:
composable(
...
) { navBackStackEntry ->
val args = navBackStackEntry.arguments
// get id param value
val id = args?.getInt("id")!!
// get showDetails param value
val showDetails = args?.getBoolean("showDetails")!!
// call profile screen composable function here
...
}
This is an example to navigate to profile screen.
val id = 7
val showDetails = true
navController.navigate("profile/$id/$showDetails")
Any Route Format Is Fine!
Instead of using this (which I prefer because it is the simplest form):
route = "profile/{id}/{showDetails}"
You can use this (required if you want showDetails
to be optional):
route = "profile/{id}/?showDetails={showDetails}"
Or this (required if you want both id
and showDetails
to be optional): :
route = "profile/?id={id}/?showDetails={showDetails}"
But please do NOT use this:
route = "profile/{id}{showDetails}"
Please make sure you at least put a separator (any string) between the navigation parameters. This navigation parameters could be parsed wrongly especially they're same data type.
If you change the route format, you need to update the navigation call too. For example:
val id = 7
val showDetails = true
navController.navigate("profile/$id/?showDetails=$showDetails")
Too Much Boilerplate Code
You may have noticed, the hard-coded strings are everywhere. One mistake can just crash the app. It is prone to errors.
So what I did is to create this NavRoute
class that has all the hard-coded strings there. I also include a utility functions (i.e. withArgs()
to build the navigation path and withArgsFormat()
to build the route
format string.
sealed class NavRoute(val path: String) {
object Login: NavRoute("login")
object Home: NavRoute("home")
object Profile: NavRoute("profile") {
val id = "id"
val showDetails = "showDetails"
}
object Search: NavRoute("search") {
val query = "query"
}
// build navigation path (for screen navigation)
fun withArgs(vararg args: String): String {
return buildString {
append(path)
args.forEach{ arg ->
append("/$arg")
}
}
}
// build and setup route format (in navigation graph)
fun withArgsFormat(vararg args: String) : String {
return buildString {
append(path)
args.forEach{ arg ->
append("/{$arg}")
}
}
}
}
Some usage examples:
// navigate to home
navController.navigate(NavRoute.Home.path)
// navigate to search
navController.navigate(NavRoute.Search.withArgs(query))
// setup route for search screen with query param
route = NavRoute.Search.withArgsFormat(NavRoute.Search.query)
Final Thoughts
I'm not sure my NavRoute approach above is the good one. I'm also not sure if it makes the code unreadable? Maybe a bit? However, it at least can get rid of many hard-coded strings and no more boilerplate code.
There is a Compose Destinations library which removes even more boilerplate code. I think it is better to understand the fundamental first before trying out this library.
Here are the steps to convert this app to use this library:
Source Code
GitHub Repository: Demo_SimpleNavigationCompose
Originally published at https://vtsen.hashnode.dev.
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