MutableState

In Jetpack Compose, mutableState() is a function that is used to create a mutable state object in which you can store and manage data that is used by a composable function. This function allows you to change the value of the state object, which will trigger a recomposition of the UI, updating the UI elements that are affected by the change.

The mutableState() function takes an initial value as an argument and returns a MutableState object, which has two properties:

The current value of the state object.
A setter function that can be used to change the value of the state object.
Here’s an example of how to use mutableState() to create a counter that can be incremented or decremented:

val count = mutableState(0)

@Composable
fun Counter() {
    Column {
        Text("Count: ${count.value}")
        Button(onClick = { count.value-- }) {
            Text("-")
        }
        Button(onClick = { count.value++ }) {
            Text("+")
        }
    }
}

In this example, the count variable is created using the mutableState() function, with an initial value of 0. The Counter composable function displays the current value of the count, and two buttons that can be used to decrement or increment the count.

It’s important to note that mutableState should be used with care, it’s best practice to use it only when you want to change something in the UI based on the user interaction and not for any other purpose.

Also, if the state is not used in the composable, the recomposition will not happen, and it could lead to some performance issues.

Remember

In Jetpack Compose, remember { mutableState() } is a function that is used to create a mutable state object that is remembered across different compositions. This means that the state object is not recreated every time the composable function is recomposed, and its value is retained between compositions.

When a composable function is recomposed, the state objects that are created within the function are also recreated, which can lead to unnecessary work and performance issues. By using remember { mutableState() }, you can ensure that the state object is only created once and its value is retained between compositions.

Here’s an example of how to use remember { mutableState() } to create a counter that can be incremented or decremented:

val count = remember { mutableState(0) }

@Composable
fun Counter() {
    Column {
        Text("Count: ${count.value}")
        Button(onClick = { count.value-- }) {
            Text("-")
        }
        Button(onClick = { count.value++ }) {
            Text("+")
        }
    }
}

In this example, the count variable is created using remember { mutableState() }, with an initial value of 0. The Counter composable function displays the current value of the count, and two buttons that can be used to decrement or increment the count.

It’s important to note that using remember { mutableState() } is only necessary when a composable function is recomposed multiple times and the state object is used in the composable function. If the state object is not used in the composable function, it will not have any impact on the performance.

LiveData

You can listen to LiveData by using the remember { liveData() } function and the state composable.

The remember { liveData() } function is used to create a LiveData object that is remembered across different compositions. This means that the LiveData object is not recreated every time the composable function is recomposed, and its value is retained between compositions.

The state composable is used to observe the LiveData object and to update the UI when the value of the LiveData object changes.

Here’s an example of how to use remember { liveData() } and the state composable to listen to a LiveData object:

val data = remember { liveData(initialValue = "Hello World") }

@Composable
fun MyText() {
    state(data) { value ->
        Text(value)
    }
}

In this example, the data variable is created using remember { liveData() }, with an initial value of “Hello World”. The MyText composable function uses the state composable to observe the data variable, which is a LiveData object, and updates the UI with the latest value of the LiveData object.