AttributeError: 'str' object has no attribute '_build_add_commands'

[hinayand]

Hi guys and gals. I want to switch the View in my Flet application, but I'm having some problems implementing this function
I have written a function that will return an object of type "ft.View"

def choose_small_tools():
    small_tools_list = ft.ListView(expand=True, spacing=10)
    small_tools_list.controls = ["A", "B", "C"]
    view = ft.View("/tools", [
            ft.Column([
                ft.Row([
                    ft.Text(value="Tools", style=ft.TextThemeStyle.TITLE_LARGE),
                ]),
                ft.Row([
                    small_tools_list
                ]),
                ft.Row([
                    ft.ElevatedButton(text="Launch", on_click=None),
                    ft.ElevatedButton(text="Back to home page", on_click=lambda _: page.go("/"))
                ])
            ])
        ])
    return view

Then I specified page.on_route_change and page.on_view_pop in the main function:

    def view_pop(view):
        page.views.pop()
        top_view = page.views[-1]
        page.go(top_view.route)

    def route_change(route: ft.RouteChangeEvent):
        page.views.clear()
        page.views.append(index())
        if route.route == "/tools":
            page.views.append(choose_small_tools())
        page.update()

Finally, when I tried to switch pages, my program reported the following error.

Exception in thread Thread-9 (go_to_small_tools):
Traceback (most recent call last):
  File "C:\Users\yang2\AppData\Local\Programs\Python\Python311\Lib\threading.py", line 1038, in _bootstrap_inner
    self.run()
  File "C:\Users\yang2\AppData\Local\Programs\Python\Python311\Lib\threading.py", line 975, in run
    self._target(*self._args, **self._kwargs)
  File "C:\Users\yang2\Desktop\WiteboardTools\main.py", line 60, in go_to_small_tools
    page.go("/tools")
  File "C:\Users\yang2\AppData\Local\Programs\Python\Python311\Lib\site-packages\flet\page.py", line 336, in go
    self.__on_route_change.handler(
  File "C:\Users\yang2\AppData\Local\Programs\Python\Python311\Lib\site-packages\flet\event_handler.py", line 16, in handler
    h(r)
  File "C:\Users\yang2\Desktop\WiteboardTools\main.py", line 23, in route_change
    page.update()
  File "C:\Users\yang2\AppData\Local\Programs\Python\Python311\Lib\site-packages\flet\page.py", line 219, in update
    added_controls = self.__update(self)
                     ^^^^^^^^^^^^^^^^^^^
  File "C:\Users\yang2\AppData\Local\Programs\Python\Python311\Lib\site-packages\flet\page.py", line 231, in __update
    control.build_update_commands(self._index, added_controls, commands)
  File "C:\Users\yang2\AppData\Local\Programs\Python\Python311\Lib\site-packages\flet\control.py", line 328, in build_update_commands
    innerCmds = ctrl._build_add_commands(
                ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\yang2\AppData\Local\Programs\Python\Python311\Lib\site-packages\flet\control.py", line 401, in _build_add_commands
    childCmd = control._build_add_commands(
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\yang2\AppData\Local\Programs\Python\Python311\Lib\site-packages\flet\control.py", line 401, in _build_add_commands
    childCmd = control._build_add_commands(
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\yang2\AppData\Local\Programs\Python\Python311\Lib\site-packages\flet\control.py", line 401, in _build_add_commands
    childCmd = control._build_add_commands(
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  [Previous line repeated 1 more time]
AttributeError: 'str' object has no attribute '_build_add_commands'

[ndonkoHenri]

I can't be of great help without the some better and complete code sample, so I advice you to simply inspire yourself from these examples: https://github.com/flet-dev/examples/tree/main/python/apps/routing-navigation

[hinayand]

I will provide the full code below, but there may be Chinese characters (because I am Chinese and my program is designed for Chinese people)

import flet as ft


def main(page: ft.Page):
    page.window_width = 300
    page.window_height = 400
    page.fonts = {
        "清晰黑": "fonts/LXGWNeoXiHei.ttf"
    }
    page.theme = ft.Theme(font_family="清晰黑")
    page.title = "白板工具箱"

    def view_pop(view):
        page.views.pop()
        top_view = page.views[-1]
        page.go(top_view.route)

    def route_change(route: ft.RouteChangeEvent):
        page.views.clear()
        page.views.append(index())
        if route.route == "/tools":
            page.views.append(choose_small_tools())
        page.update()

    def choose_small_tools():
        small_tools_list = ft.ListView(expand=True, spacing=10)
        small_tools_list.controls = ["计时器", "时钟", "抽学号"]
        view = ft.View("/tools", [
            ft.Column([
                ft.Row([
                    ft.Text(value="小工具", style=ft.TextThemeStyle.TITLE_LARGE),
                ]),
                ft.Row([
                    small_tools_list
                ]),
                ft.Row([
                    ft.ElevatedButton(text="启动", on_click=None),
                    ft.ElevatedButton(text="返回首页", on_click=lambda _: page.go("/"))
                ])
            ])
        ])
        return view

    def index():
        view = ft.View("/")
        view.controls = [
            ft.Column([
                ft.Row([
                    ft.Text(value="白板工具箱", style=ft.TextThemeStyle.TITLE_LARGE)
                ]),
                ft.Row([
                    ft.ElevatedButton(text="小工具", on_click=go_to_small_tools, width=260)
                ])
            ])
        ]
        view.vertical_alignment = ft.MainAxisAlignment.CENTER
        return view

    def go_to_small_tools(e):
        page.go("/tools")
        page.update()

    page.on_route_change = route_change
    page.on_view_pop = view_pop
    page.go(page.route)


ft.app(target=main, assets_dir="./resource")

In the meantime, I've seen the example on the official website, except that I don't know why this problem occurs.

[ndonkoHenri]

The problem comes from this line:

small_tools_list.controls = ["计时器", "时钟", "抽学号"]

The controls property takes a list of Controls and not a list of strings.

By the way, add the line below to your view_pop function:

page.go(top_view.route)

[hinayand]

Thanks!