@Composable in a overridden method?

Question

I would like to draw a @Composable on a override method, like

@Composable
override fun onKeyDown(keyCode: Int, event: KeyEvent?): Boolean {
    Greeting()
}

Unfortunately, I can not mark a override onKeyDown() with @Composable, since I get:

Conflicting overloads: @Composable public open fun onKeyDown(keyCode: Int, event: KeyEvent?): Boolean defined in com.example.emptycompose.MainActivity, public open fun onKeyDown(p0: Int, p1: KeyEvent!): Boolean defined in androidx.appcompat.app.AppCompatActivity

How can I use a @Composable in e.g. a override onKeyDown()?

I think that you need to have onKeyDown() update state that is used by your composables defined elsewhere. — CommonsWare

RickSanchez725 RickSanchez725 · Accepted Answer · 2020-12-07T23:22:28

You can't directly return an instance of a composable like that, but you can have a composable that observes changes and recomposes automatically.

In your ViewModel create a MutableLiveData that holds the slider position.

    val sliderPosition = MutableLiveData<Integer>()

In your Activity, have onKeyDown update the MutableLiveData:

override fun onKeyDown(keyCode: Int, event: KeyEvent?): Boolean {
    when (event?.keyCode) {
        KeyEvent.KEYCODE_VOLUME_UP, KeyEvent.KEYCODE_VOLUME_DOWN -> {
            viewModel.sliderPosition.value = getCurrentSliderPosition()
        }
    }
}

Then pass the ViewModel as a parameter to your composable function and then you can observe volume changes like this:

   val position by viewModel.sliderPosition.observeAsState(0)

Now you can just use position as a regular variable in your layout, but when it changes, the Composable will be automatically updated with the new value.

You can read more on managing state with Compose here.

As a side note, there is an experimental (at the time of the answer) keyInputFilter Modifier you may want to check out.

@Composable in a overridden method?

1 Answers