Calling update() inside Control.did_mount() causes deadlock

[FeodorFitsner]

Sample code causing deadlock:

import flet
from flet import Container, Page, Text, UserControl

class MyControl(UserControl):
    def build(self):
        print("i am built")
        self.c = Container()
        self.c.bgcolor = "blue"
        self.c.content = Text("hello there")
        return self.c

    def did_mount(self):
        print("i am mounted")
        self.resize_me()

    def resize_me(self):
        self.c.bgcolor = "red"
        self.update()

def main(page: Page):
    t = MyControl()
    page.add(t)
    print("i am added")

flet.app(target=main)

Solution:

Go through a list of added controls after update() is finished and lock released and call did_mount() for each added control.

[ndonkoHenri]

Hey, will it now be possible to easily access self.page in the UserControl?

[FeodorFitsner]

Sure, it's possible now.

[ItsCubeTime]

Hi, coming from #488 which was merged in favor of this. The issue described there still seems present in both 0.3.0.dev941 & 0.2.4 on Pypi.

import flet

class userCtrl(flet.UserControl):
    def build(self):
        return [flet.Container(bgcolor=flet.colors.RED, width=self.page.width, height=100000)]

def main(page: flet.Page):
    page.add(
        userCtrl()
    )

flet.app(
    target=main, web_renderer="html", assets_dir=".", port=3768
    # , view=flet.WEB_BROWSER
)

PS C:\Users\olliv\Desktop\Art And Development\Flutter Learning\Flet\Calculator example> python -u "f:\Olliver\Art and development\Flutter Learning\Flet\Calculator example\selfPageBug.py"
Unhandled error processing page session 07cc183d-3ca2-4055-bcd2-0a70433d1b61: Traceback (most recent call last):
  File "C:\Users\olliv\AppData\Local\Programs\Python\Python310\lib\site-packages\flet\flet.py", line 220, in on_session_created
    session_handler(page)
  File "f:\Olliver\Art and development\Flutter Learning\Flet\Calculator example\selfPageBug.py", line 8, in main
    page.add(
  File "C:\Users\olliv\AppData\Local\Programs\Python\Python310\lib\site-packages\flet\page.py", line 256, in add
    added_controls = self.__update(self)
  File "C:\Users\olliv\AppData\Local\Programs\Python\Python310\lib\site-packages\flet\page.py", line 231, in __update
    control.build_update_commands(self._index, added_controls, commands)
  File "C:\Users\olliv\AppData\Local\Programs\Python\Python310\lib\site-packages\flet\control.py", line 353, in build_update_commands
    innerCmds = ctrl._build_add_commands(
  File "C:\Users\olliv\AppData\Local\Programs\Python\Python310\lib\site-packages\flet\control.py", line 401, in _build_add_commands
    childCmd = control._build_add_commands(
  File "C:\Users\olliv\AppData\Local\Programs\Python\Python310\lib\site-packages\flet\control.py", line 381, in _build_add_commands
    self._build()
  File "C:\Users\olliv\AppData\Local\Programs\Python\Python310\lib\site-packages\flet\user_control.py", line 12, in _build
    content = self.build()
  File "f:\Olliver\Art and development\Flutter Learning\Flet\Calculator example\selfPageBug.py", line 5, in build
    return [flet.Container(bgcolor=flet.colors.RED, width=self.page.width, height=100000)]
AttributeError: 'NoneType' object has no attribute 'width'

[FeodorFitsner]

self.page is available in did_mount() method only: #488 (comment)

Control tree is updated with a page instance only after its changes sent to a UI.

[ItsCubeTime]

Ah I see

Thank you for clarifying