Solara•3mo ago

Trying to understand state management

If I have a reusable component with an internal state value = use_reactive(42) linked to an IntSlider and I have multiple of these components on my page, how do I then get the values of all nested slider components to e.g. use in another component? e.g.

@solara.component
def SliderComponent():
    slider_value = solara.use_reactive(42)
    solara.IntSlider('', slider_value.value, min=0, max=50)

@solara.component
def MyApp():
    SliderComponent()
    SliderComponent()

    SomeComponentThatUsesTheValuesOfAllSliders()

@solara.component
def SliderComponent():
    slider_value = solara.use_reactive(42)
    solara.IntSlider('', slider_value.value, min=0, max=50)

@solara.component
def MyApp():
    SliderComponent()
    SliderComponent()

    SomeComponentThatUsesTheValuesOfAllSliders()

4 Replies

Dave Hirschfeld•3mo ago

Is the recommended way to inject reactive variables into reusable components from the outer scope? e.g.

@solara.component
def SliderComponent(value: int | Reactive[int] = 0) -> None:
    if not isinstance(value, Reactive):
        slider_value = solara.use_reactive(value)
    else:
        slider_value = value
    solara.IntSlider('', slider_value.value, min=0, max=50)

@solara.component
def MyApp():
    slider1 = solara.use_reactive(21)
    slider2 = solara.use_reactive(42)
    SliderComponent(slider1)
    SliderComponent(slider2)
    SomeComponentThatUsesTheValuesOfAllSliders(
        slider1, slider2,
    )

@solara.component
def SliderComponent(value: int | Reactive[int] = 0) -> None:
    if not isinstance(value, Reactive):
        slider_value = solara.use_reactive(value)
    else:
        slider_value = value
    solara.IntSlider('', slider_value.value, min=0, max=50)

@solara.component
def MyApp():
    slider1 = solara.use_reactive(21)
    slider2 = solara.use_reactive(42)
    SliderComponent(slider1)
    SliderComponent(slider2)
    SomeComponentThatUsesTheValuesOfAllSliders(
        slider1, slider2,
    )

MaartenBreddels•3mo ago

Hi Dave, good questions. use_reactive already does what you want to do, so you can remove the if (actually hooks - function prefixed with use_ - should not be conditional). I've put together a working example that demos a few of these ideas:

import solara

value_app = solara.reactive(3)

@solara.component
def SliderComponent(label, value: int | solara.Reactive[int] = 0) -> None:
    # will convert to reactive, if not already a reactive
    slider_value = solara.use_reactive(value)
    solara.IntSlider(label, slider_value, min=0, max=50)


@solara.component
def ValueOnlyComponent(*values: list[int]):
    solara.Text(repr(values))

# this component is not reusable (pratically speaking)
# because it uses application wide state.
# it's main use is seperation of concerns, code organization
# and possibly putting the same component in two places
@solara.component
def SliderApp() -> None:
    solara.IntSlider('SliderApp', value_app, min=0, max=50)


@solara.component
def Page():
    slider1 = solara.use_reactive(21)
    slider2 = solara.use_reactive(42)
    with solara.Card("State management"):
        # note that slider2.value is never updated, because it's being pass by value
        ValueOnlyComponent(slider1.value, slider2.value, value_app.value)
        SliderComponent('reactive slider1', slider1)
        SliderComponent('value slider2', slider2.value) # passes value, so will not sync back the value
        # application wide state in combination with a reusable component that can take a reactive value
        SliderComponent('using value_app', value_app)
        SliderApp()

import solara

value_app = solara.reactive(3)

@solara.component
def SliderComponent(label, value: int | solara.Reactive[int] = 0) -> None:
    # will convert to reactive, if not already a reactive
    slider_value = solara.use_reactive(value)
    solara.IntSlider(label, slider_value, min=0, max=50)


@solara.component
def ValueOnlyComponent(*values: list[int]):
    solara.Text(repr(values))

# this component is not reusable (pratically speaking)
# because it uses application wide state.
# it's main use is seperation of concerns, code organization
# and possibly putting the same component in two places
@solara.component
def SliderApp() -> None:
    solara.IntSlider('SliderApp', value_app, min=0, max=50)


@solara.component
def Page():
    slider1 = solara.use_reactive(21)
    slider2 = solara.use_reactive(42)
    with solara.Card("State management"):
        # note that slider2.value is never updated, because it's being pass by value
        ValueOnlyComponent(slider1.value, slider2.value, value_app.value)
        SliderComponent('reactive slider1', slider1)
        SliderComponent('value slider2', slider2.value) # passes value, so will not sync back the value
        # application wide state in combination with a reusable component that can take a reactive value
        SliderComponent('using value_app', value_app)
        SliderApp()

Run and edit this code snippet at PyCafe Hope this helps (btw, you can run and edit the code snippet if you click the link)

Dave Hirschfeld•3mo ago

Thanks @MaartenBreddels! I'm just trying to figure out how best to structure a solara app and I think that aligns with what I'm envisaging - only use globals for application-wide state and otherwise inject reactive variables into the components 🤔

MaartenBreddels•3mo ago

yeah, that's a good approach. When possible, it's even better to not pass reactive variables if they do not mutate them (just pass .value)

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