Attaching a "on" handler dynamically to widget

[FredoVelcro]

Hello,

Is there a way to manually attach an handler (eg: on_key, on_mouse_down etc) to a given widget dynamically ?
eg :

def decorate(mywidget: Widget)
    mywidget.add_handler('key', mycallback) <= or something like this

The widget may have already registered handlers so may keep in this case and add mine.
Message Pump maybe ?

Thank you for any help.
Best regards,
Fred

[willmcgugan]

The short answer is "no".

The closest that Textual supports is the message_signal attribute on widgets. You can subscribe to that and get a callback for any widget sent to that app.

However, this sounds like an XY problem. There is almost certainly a better way to accomplish what you are trying to solve. Could you elaborate on the problem you are tackling?

[FredoVelcro]

Hello Will,

First thanks for your quick response :)
Textual is really amazing, i would like to congratulate, it's really good job !

This is a POC but makes app freeze (BEWARE) and nothing detected :

from textual.app import App, ComposeResult
from textual.widgets import Static
from textual.events import MouseDown
from textual import events
from textual import log
from textual.widget import Widget

class WidgetHandler():
    def __init__(self, widget: Widget):
        self.widget = widget
        self.widget.message_signal.subscribe(self.widget, self.handle, False)
    
    def handle(self, event) -> None:
        log("event ok")

class Demo(App[None]):
    CSS = """
    #t {
        width: 100%;
        height: 100%;
        background: #1f6feb;
        color: white;
        content-align: center middle;
        text-style: bold;
    }
    """
    BINDINGS = [("q", "quit", "Quit app")]

    def compose(self) -> ComposeResult:
        yield Static("click here", id="t")

    def on_mount(self) -> None:
        try:
            w: Static = self.query_one("#t", Static)
            handler = WidgetHandler(w)
        except Exception as e:
            log(e)

    def action_quit(self) -> None:
        self.exit()

if __name__ == "__main__":
    Demo().run()

I know that i could have done it with "@on" decorator or "on_key()" method on custom Static, but in my case, it's like here : i'm given a Widget (or custom) and i need to "plug" events support.

Note: using textual console, i can see that Static natively "see" all events (keys, mouse), so may have a way to catch them without defining a new "MyStatic" with "on_key" etc

(BEWARE, app freezes terminal here)

Thank you again.

Fred

[Zaloog]

Hi @FredoVelcro ,
You can define the handlers also on your Custom Widgets directly. Or define handlers with ids and create the widgets with the specified id.

can you elaborate, whats the purpose of your Approach, and why you do not want to use the suggested approach.
If we get a better understanding there, we might be able to provide better help.

best regards
Lars

[FredoVelcro]

Hello Lars,

Thanks for your help too :)

In fact, underlying problem as you could have understood is : can we handle events (key, mouse) on a widget if handlers not first set in its declaration ?
At first I thought that as handlers are plugged at app start (fetching @on annotations, or on_* methods), there was a common public api to do this manually...

But, as you both tell me, i think the only way is to subclass the concerned widget... (widget.message_signal is hard to place...)

Best regards,

Fred

[Zaloog]

I understand what you want to achive, but also would be interested to understand, why you want it that way.

Because you dont want to create custom widgets?