introduce on_startup to schedule synchronous or asynchronous startup tasks

nicegui/nicegui.py

@@ -1,4 +1,5 @@
 #!/usr/bin/env python3
+from typing import Awaitable, Callable
 import justpy as jp
 import uvicorn
 import sys
@@ -46,6 +47,8 @@ async def binding_loop():
 @jp.app.on_event('startup')
 def startup():
     [jp.run_task(t) for t in Timer.tasks]
+    [t() for t in Ui.startup_tasks if isinstance(t, Callable)]
+    [jp.run_task(t) for t in Ui.startup_tasks if isinstance(t, Awaitable)]
     jp.run_task(binding_loop())
 
 Element.wp = wp

nicegui/timer.py

@@ -1,6 +1,7 @@
 import asyncio
 import time
 import traceback
+from typing import Awaitable
 from binding import BindableProperty
 from .elements.element import Element
 from .utils import handle_exceptions
@@ -11,7 +12,7 @@ class Timer:
 
     active = BindableProperty
 
-    def __init__(self, interval, callback, *, active=True, once=False):
+    def __init__(self, interval: float, callback: Awaitable, *, active: bool = True, once: bool = False):
         """Timer
 
         One major drive behind the creation of NiceGUI was the necessity to have a simple approach to update the interface in regular intervals, for example to show a graph with incomming measurements.

nicegui/ui.py

@@ -1,3 +1,6 @@
+from typing import Awaitable, Callable, List, Union
+
+
 class Ui:
 
     from .elements.button import Button as button
@@ -25,3 +28,9 @@ class Ui:
     from .elements.card import Card as card
 
     from .timer import Timer as timer
+
+    startup_tasks: List[Union[Callable, Awaitable]] = []
+
+    def on_startup(self, task: Union[Callable, Awaitable]):
+
+        self.startup_tasks.append(task)