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Jetpack Compose — Composable lifecycle consciousness | by Saqib | June 2023

Composable lifecycle conscious?

Each Composable has a lifecycle proprietor LocalLifeCycleOwner.present which we’ll use so as to add an observer to the View lifecycle occasions and react to them. We additionally want to verify to take away that observer when the View is destroyed and the Composable leaves the Element. DisposableEffect The Facet Results API is a perfect alternative right here so as to add an observer and it gives onDispose block for cleanup.

In case you are not accustomed to DisposableEffect API or wish to discover intimately, I wrote an in depth story about DisposableEffect API and its comparability with LaunchedEffect And bear in mind(key). You may learn from hyperlink.

The code under reveals how DisposableEffect What does the API implementation seem like after including and eradicating lifecycle occasion observers.

Please replace the code additional to bear in mind present lifecycle occasion right into a state variable lifecycleEvent and prolong the earlier instance to react above lifecycle occasion.

Within the above code, it remembers a state variable lifecycleEvent Up to date from inside DisposableEffect. IN NewsScreen synthesis added LaunchedEffect with lifecycleEvent like a key and name fetchNews inside lambda each time lifecycleEvent To be ON_RESUME standing. This may make NewsScreen artificiallifecycle-aware . (Code for NewsViewModel will stay as it’s uncovered fetchNews methodology)

Now everytime the View seems Resume says it fetches Information and the View is up to date with the newest content material that meets our new information use case coming from the background.

What if there are various Composables that have to be lifecycle-aware? Then make this code reusable for different synthesizers.

Check out the reusable code snippet under.

Code inside NewsScreen composable turns into easier and extra readable as a result of all of the code is being noticed lifecycle occasions handed to a generic Composable are internally memoized lifecycle state for that individual Composable. NewsScreen simply take lifecycle phrase standing rememberLifecycleEvent Will be mixed and become a key for LaunchedEffect That is the information on ON_RESUME.

In case you are not accustomed to LaunchedEffect . I wrote an in depth story about LaunchedEffect And rememberCoroutineScope Uncomfortable side effects API you possibly can learn from hyperlink .

This resolution has one downside: LaunchedEffect not activated on ON_CREATE and first ON_START life cycle occasions, LaunchedEffect simply begin to hear the phrase ON_RESUME life cycle occasions onwards. Additionally LaunchedEffect means to run droop features associated to the person interface.

A sensible use case could be to document analytics occasions when any display is opened for the primary time. To realize that we should pay attention ON_CREATE occasions to log analytics occasions, so we have to discover one other resolution to have the ability to react on ON_START/ON_CREATE life cycle occasions.

We’ll use DisposableEffect API to pay attention lifecycle occasions and react to them in DisposableEffect API impact block. We additionally wish to make the answer reusable in order that it may be built-in into different Compound Objects.

Check out the code under

DisposableEffectWithLifecycle composable takes lambda parameter for all lifecycle occasion, observer lifecycle occasions and implement particular strategies on every lifecycle occasion. DisposableEffectWithLifecycle commentary packing lifecycle occasions and cleanup when leaving the Element. Its resolution is reusable and could be simply mixed inside every other composable machine to make that composable lifecycle conscious.

It solves our issues and gives the above information ON_CREATE And ON_START in addition to our earlier resolution failed.

It is a affordable resolution however we are able to even enhance shifting such code contained in the ViewModel the place our ViewModel will observe lifecycle occasion and can react.

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Updated: June 13, 2023 — 6:48 am

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