v1: Generator event handlers

[FeodorFitsner]

Allow event handlers with yield inside (making them generators) to call auto-update on yield.

Example:

import asyncio
from dataclasses import dataclass

import flet as ft

@dataclass
class AppState:
    counter: float

    async def start_counter(self):
        self.counter = 0
        yield
        for _ in range(0, 10):
            self.counter += 0.1
            yield
            await asyncio.sleep(0.5)


def main(page: ft.Page):
    state = AppState(counter=0)

    page.add(
        ft.ControlBuilder(
            state,
            lambda state: ft.Column(
                [
                    ft.ProgressBar(state.counter),
                    ft.Button("Run!", on_click=state.start_counter),
                ]
            ),
        )
    )

ft.run(main)

Screen.Recording.2025-06-19.at.2.23.13.PM.mov

Summary by Sourcery

Enable generator event handlers (sync and async) to drive incremental UI updates by yielding, and fix the auto_update target to reference controls by index.

New Features:

• Support async and sync generator event handlers to trigger auto-update on each yield.

Bug Fixes:

• Correct the target passed to auto_update to use the control index reference.