Ever tried logging impressions of components or screens in your app when they’re displayed to a user? If you’ve been down that rabbit hole, you know it’s like trying to catch the wind. Given how common this functionality it, having an out-of-the-box solution would’ve been a huge time-saver.
Enter Rebecca Franks, a Dev Rel Engineer at Google, who’s swooping in to save the day with a proposal for a new “Visibility” Modifier. This nifty Modifier aims to track visibility changes of a Composable easily. It’s still a proposal because, like any good superhero, it has its kryptonite: performance implications when used in lists. But hey, it’s currently the best way to track visibility, so I encourage you to check it out. And if you’ve got opinions, suggestions, or just want to say hi, give Rebecca your feedback directly. Let’s help shape this API
/**
* `onVisibleChange` fires events when the visibility of an item changes.
*
* The event includes information such as the bounds of the visible item, and the fraction of the
* item that's visible. It'll only fire once for when the item enters the screen, and on exit, using
* the bounds within the current window to determine if an item is visible or not.
*
* _Limitations_:
* - This modifier has no way to detect if there is something on top of it - obscuring (ie z-index checking).
* - Keyboard visibility, if an item is below the keyboard, this modifier will still track
* the item as visible, it is recommended that you ensure you are using
* android:windowSoftInputMode="adjustResize" to ensure the whole window is resized and then
* items will not report themselves as being visible.
*
* See VisibilityTrackingSample.kt for example usage.
*
* @param visibleEvent function that will run when the item becomes visible or invisible.
*/
fun Modifier.onVisibilityChanged(visibleEvent: (VisibleEvent) -> Unit) =
* `onVisiblePositionChanged` fires events when the visibility of an item changes. It include the same information as `onVisibleChange`, with additional information such as
* a trigger on each position change.
*
* The event includes information such as the bounds of the visible item, and the fraction of the
* item that's visible. It'll trigger when the item enters the screen, and on exit, using
* the bounds within the current window to determine if an item is visible or not, as well as for each position change of the item on screen.
*
* WARNING: This function is invoked often if items are changing frequently (e.g. in a scrolling list), it should be use sparingly. Prefer `onVisibleChange` over this function.
*
* _Limitations_:
* - This modifier has no way to detect if there is something on top of it - obscuring (ie z-index checking).
* - Keyboard visibility, if an item is below the keyboard, this modifier will still track
* the item as visible, it is recommended that you ensure you are using
* android:windowSoftInputMode="adjustResize" to ensure the whole window is resized and then
* items will not report themselves as being visible.
*
* See VisibilityTrackingSample.kt for example usage.
*
* @param visibleEvent function that will run when the item becomes visible or invisible.
*/
fun Modifier.onVisiblePositionChanged(visibleEvent: (VisiblePositionChangedEvent) -> Unit) =
