feature: document for event mechanism for customer service/control development

[SamYuan1990]

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Describe the requested feature

We need an example for developer to design their own customer event.
The event trigger by dart code and catched by flet python code.
Specific in customer service/control development.

Suggest a solution

A document or example code, better for people feed to prompt as example.

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[FeodorFitsner]

You mean this: https://docs.flet.dev/extend/user-extensions/ ?

[SamYuan1990]

You mean this: https://docs.flet.dev/extend/user-extensions/ ?

yes, https://docs.flet.dev/extend/user-extensions/#events not only click, but looking for on_event as general case. For example, I am doing a ASR extension, so... the event maybe on_vad or on_ASR.