use_reactive

Creates a reactive variable with the a local component scope.

def use_reactive(
    value: Union[T, solara.Reactive[T]],
    on_change: Optional[Callable[[T], None]] = None,
) -> solara.Reactive[T]:

    ...

It is a useful alternative to use_state when you want to use a reactive variable for the component state. See also our documentation on state management.

If the variable passed is a reactive variable, it will be returned instead and no new reactive variable will be created. This is useful for implementing component that accept either a reactive variable or a normal value along with an optional on_change callback.

Arguments:

• value (Union[T, solara.Reactive[T]]): The value of the reactive variable. If a reactive variable is provided, it will be used directly. Otherwise, a new reactive variable will be created with the provided initial value. If the argument passed changes the reactive variable will be updated.

• on_change (Optional[Callable[[T], None]]): An optional callback function that will be called when the reactive variable's value changes.

Returns: solara.Reactive[T]: A reactive variable with the specified initial value or the provided reactive variable.

Examples

Replacement for use_state

import solara

@solara.component
def ReusableComponent():
    color = solara.use_reactive("red")  # another possibility
    solara.Select(label="Color",values=["red", "green", "blue", "orange"],
                value=color)
    solara.Markdown("### Solara is awesome", style={"color": color.value})

@solara.component
def Page():
    # this component is used twice, but each instance has its own state
    ReusableComponent()
    ReusableComponent()

Flexible arguments

The MyComponent component can be passed a reactive variable or a normal Python variable and a on_value callback.

import solara
from typing import Union, Optional, Callable

@solara.component
def MyComponent(value: Union[T, solara.Reactive[T]],
                on_value: Optional[Callable[[T], None]] = None,
    ):
    reactive_value = solara.use_reactive(value, on_value)
    # Use the `reactive_value` in the component