Is there any callback or listener to get an event ...

# compose

[_shtomar]

Is there any callback or listener to get an event when Composable rendered it’s content for first time or it’s content is changed?

[nglauber]

you can achieve something similar using this:

@Composable
fun Foo() {
    // ...
    LaunchedEffect(Unit) {
        // This code will run just on
        // the first composition
    }
}

However, if you remove Foo from the composition, it will be called again…
For instance:

if (someFlag) {
    Foo()
} else {
    Bar()
}

every time you set someFlag to true, the code inside the LaunchedEffect will be executed.

[Adam Powell]

What are you looking to use that callback event to do? Like @nglauber mentions above you can use the effect APIs to publish data about a recomposition, but there are many ways content can change and we try very hard to make sure that as many of them as possible have fast paths that skip running as much code as possible, and depending on what you want this for you might find yourself scratching your head as to why you aren't getting a callback you expect.

[_shtomar]

Thank @nglauber

[_shtomar]

I am changing content of the Composable. Basically I need a callback whenver the content of the Composable changes

[K Merle]

I think in that case you can replace Unit with the value of the content. So if you want to call LaunchedEffect when title changes only, you could do

@Composable
fun Foo() {
    // ...
    LaunchedEffect(title) {
        // This code will run just on
        // the first composition
    }
}