I'm new in jetpack compose and trying to understand the difference between remember and mutableStateOf
In other words the deference between this line
val text = remember{ mutableStateOf("") }
and this
val text = remember{ "" }
and this also
val text = mutableStateOf("")
remember is a composable function that can be used to cache expensive operations. You can think of it as a cache which is local to your composable.
val state: Int = remember { 1 }
The state in the above code is immutable. If you want to change that state and also update the UI, you can use a MutableState. Compose will observe any reads/writes the MutableState object and trigger a recomposition to update the UI.
val state: MutableState<Int> = remember { mutableStateOf(1) }
Text(
modifier = Modifier.clickable { state.value += 1 },
text = "${state.value}",
)
Another variant (added in alpha12) called rememberSaveable which is similar to remember, but the stored value can survive process death or configuration changes.
val state: MutableState<Int> = rememberSaveable { mutableStateOf(1) }
Note: You can also use property delegates as a syntactic sugar to unwrap the MutableState.
var state: Int by remember { mutableStateOf(1) }
Regarding the last part of your question:
val text = mutableStateOf("")
MutableState is an alternative to using LiveData or Flow. Compose does not observe any changes to this object by default and therefore no recomposition will happen. If you want the changes to be observed and the state to be cached use remember. If you don't need the caching but only want to observe, you can use derivedStateOf. Here is a sample of how to use it.
As pointed out by Ahmad Hamwi in the comments and quoting them:
Compose does observe the value of the state, in fact there's a @Stable annotation on top of it, and that's its sole responsibility, but since we're not remembering the state, a mutableStateOf(1) will always be created AGAIN, so there will be a new instance of a state, but will still have the same value of 1. So the state seems to not change, but there IS a recomposition happening.