More in-depth examples on message passing?

[igorfil]

Hi,

I really love the Textual! One thing I would like to understand better is message passing.

There are not many examples really and I did not find documentation. From the discussions and the Calculator example it is more or less clear how to pass messages between widgets. What I would like to know is how to pass messages into the Textual App from the outside? I.e. when Textual is only a frontend for a bigger application, possibly running multiple threads.

For example, I have a thread that processes some data, and when it's done, I would like it to be displayed. I would like to understand how to pass a message with data to be displayed into the Textual App and then channel it to a proper Widget that will render it.

Is there any examples that would show proper ways of doing that?

[zed]

As I see it, builtin messages are used by widgets to bubble up events such as Button.Pressed https://textual.textualize.io/guide/events/
reactive/var can be used by a parent widget for the opposite top-down direction. https://textual.textualize.io/guide/reactivity/
There is also experimental (for internal use) textual.signal: having a signal, widgets can subscribe; signal owner publishes e.g., app.theme_changed_signal.

More generally, event-related Python packages follow Observer/Publish-subscribe patterns (there is a dispatch/message bus object in the latter case). For example, your UI code responsible for displaying model.some_attr can connect to changes in your model object: model.events.some_attr.connect(callback) and the code responsible for updating the value: model.some_attr = new_value--assuming something like https://pypi.org/project/psygnal/ (similar to Qt's Signals & Slots API). To handle multiple threads, there may be additional steps such as .connect(thread="current") & .emit_queued().