Where is the object of ExploreModel created?

Question

The following code is the project.

I don't understand fully the code onExploreItemClicked = { launchDetailsActivity(context = this, item = it) } in class MainActivity .

The fun launchDetailsActivity requires two paramaters which are Context and ExploreModel.

One of paramater is Context which is assigned with this, it's OK;

Another of paramater is ExploreModel which is assigned with it, I don't know where the object ExploreModel which is represented with it is created, could you tell me?

@AndroidEntryPoint
class MainActivity : ComponentActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        WindowCompat.setDecorFitsSystemWindows(window, false)

        setContent {
            ProvideWindowInsets {
                ProvideImageLoader {
                    CraneTheme {
                        MainScreen(
                            onExploreItemClicked = { launchDetailsActivity(context = this, item = it) }
                        )
                    }
                }
            }
        }
    }
}


@Composable
fun MainScreen(onExploreItemClicked: OnExploreItemClicked) {
   ...
}


typealias OnExploreItemClicked = (ExploreModel) -> Unit


fun launchDetailsActivity(context: Context, item: ExploreModel) {
    context.startActivity(createDetailsActivityIntent(context, item))
}

user_6395627 · Answer

The argument for onExploreItemClicked is an implementation of (ExploreModel) -> Unit. That function type is created via a lambda expression. In Kotlin, if a lambda has only one parameter then that parameter can be omitted and it's given the implicit name of it.

So in this case, it is the ExploreModel instance passed to the function when invoked. Which instance that will be is likely dependent on which "explore item" is clicked on the screen. I haven't properly read all the code, but I did find this in ExploreSection.kt (by following the code starting with the construction of MainScreen):

@OptIn(ExperimentalCoilApi::class) 
@Composable 
private fun ExploreItem(
    modifier: Modifier = Modifier,
    item: ExploreModel,
    onItemClicked: OnExploreItemClicked ) {
    Row(
        modifier = modifier
            .clickable { onItemClicked(item) }
            .padding(top = 12.dp, bottom = 12.dp)
    ) { 

/* REST OMITTED FOR BREVITY */

It accepts the OnExploreItemClicked instance, as well as an ExploreModel instance. Then, in the clickable labmda, it invokes the OnExploreItemClicked function:

.clickable { onItemClicked(item) }

And it passes in the associated ExploreModel instance. Of course, that only tells you where it (that we previously talked about) gets its value, but it doesn't tell you where the ExploreModel instance is actually created. You'd have to explore the code more to see where ExploreItem is called, and where it gets the model (I believe it at least comes from the view model).

Note if you don't want to use the implicit it, then you can give the parameter an explicit name (and type, if wanted). For example:

MainScreen(
    onExploreItemClicked = { model: ExploreModel -> launchDetailsActivity(context = this, item = model) }
)

Where is the object of ExploreModel created?

1 Answers