reflex/docs/events/yield_events.md

import reflex as rx

Yielding Multiple Updates

A regular event handler will send a StateUpdate when it has finished running. This works fine for basic event, but sometimes we need more complex logic. To update the UI multiple times in an event handler, we can yield when we want to send an update.

To do so, we can use the Python keyword yield. For every yield inside the function, a StateUpdate will be sent to the frontend with the changes up to this point in the execution of the event handler.

import asyncio

class MultiUpdateState(rx.State):
    count: int = 0

    async def timed_update(self):
        for i in range(5):
            await asyncio.sleep(0.5)
            self.count += 1
            yield


def multi_update():
    return rx.vstack(
    rx.text(MultiUpdateState.count),
    rx.button("Start", on_click=MultiUpdateState.timed_update)
)

Here is another example of yielding multiple updates with a loading icon.

import asyncio

class ProgressExampleState(rx.State):
    count: int = 0
    show_progress: bool = False

    async def increment(self):
        self.show_progress = True
        yield
        # Think really hard.
        await asyncio.sleep(0.5)
        self.count += 1
        self.show_progress = False

def progress_example():
    return rx.cond(
        ProgressExampleState.show_progress,
        rx.chakra.circular_progress(is_indeterminate=True),
        rx.heading(
            ProgressExampleState.count,
            on_click=ProgressExampleState.increment,
            _hover={"cursor": "pointer"},
        )
    )