Binding a key to scroll MarkdownViewer

[tthkbw]

I have written a lot of Python, but am not really fluent in classes and object oriented programming--I was a C and Verilog person for many years . . .

So I am trying to bind the 'j' and 'k' keys to scroll the MarkdownViewer in the example program markdown.py. I think what I want to do is bind 'j', for example, to generate a MouseScrollDown event, but I have no idea how to generate an event.

Either that, or figure out how to rewrite the scroll_down and scroll_up functions that are in widget.py so that they reference my instance of MarkdownViewer. This seems complicate (particularly to me!) since the code already exists, I just need to figure out how to reference it.

The only success I've had is to hack the widget.py source and add my bindings there. That works, but obviously isn't a solution.

If someone can point me to an example that does a binding like this that would be perfect--I can learn from it.

[davep]

Unless otherwise told not to, bindings inherit. So you can generally inherit from a widget and add your own bindings. For example:

from pathlib import Path

from textual.app     import App, ComposeResult
from textual.widgets import Header, Footer, MarkdownViewer
from textual.binding import Binding

class ViLikeMarkdownViewer( MarkdownViewer ):

    BINDINGS = [
        Binding( "j", "up", "", show=False ),
        Binding( "k", "down", "", show=False ),
    ]

    def action_up( self ) -> None:
        self.scroll_up()

    def action_down( self ) -> None:
        self.scroll_down()

class ViLikeMarkdownApp( App[ None ] ):

    def compose( self ) -> ComposeResult:
        yield Header()
        yield ViLikeMarkdownViewer( Path( "../textual/README.md" ).read_text() )
        yield Footer()

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

[TomJGooding]

I was just about to post something similar Dave but you beat me to it!

However my example simply used the scroll_up / scroll_down methods inherited from the class - just wondering if you would instead recommend defining new methods or was this just showing how to use Textual's actions?

class VLikeMarkDownViewer(MarkdownViewer):
    BINDINGS = [
        ("j", "scroll_down", "Scroll Down"),
        ("k", "scroll_up", "Scroll Up"),
    ]


class MarkdownApp(App):
    ...

[davep]

Mostly comes down to me constantly thinking bindings only work with actions. 🤦🏻‍♀️

(Although I do sort of like how they're a similar in feel to Emacs interactive functions vs normal functions)

[tthkbw]

Thanks to both of you for the quick response. I was close in my messing around, but hadn't created the new class based on MarkdownViewer.

On the the next thing--I am playing with creating a command line epub reader using Textual. I have used Rich to build a book database manager and created all sorts of pretty tables and bar graphs and such.