Support for passing functions as layout (dynamic layouts)

[rpkyle]

As with the other implementations of Dash, Dash.jl should support passing functions (not just components) to layout. This is described in more detail (Dash for Python) in https://github.com/plotly/dash-docs/issues/172 and https://github.com/plotly/dash-docs/pull/201.

[rpkyle]

This was resolved by #18, closing.

[alexcjohnson]

Does this actually work the same way as in Python? What I mean is, when layout is a function in Python, every time a user requests the app index page, the layout function executes again - so in principle you can use that to refresh a database query or something.

It looks to me as though in the current Julia implementation this function is only evaluated when you start the server. Am I interpreting this correctly?

[waralex]

@alexcjohnson

layout_data(layout::Component) = layout
layout_data(layout::Function) = layout()
function process_layout(request::HTTP.Request, state::HandlerState)

    return HTTP.Response(
        200,
        ["Content-Type" => "application/json"],
        body = JSON2.write(layout_data(state.app.layout))
    )
end

function layout_data have 2 overloads (methods in Julia terms) - one used if layout is a Component and another if layout is a function.

This is about precessing the layout. To be honest, I didn't really understand how layout is related to the index_page query, which generates only the basic html of the page.

[alexcjohnson]

OK great - just wanted to check. Looks like we are indeed all set 🎉

To be honest, I didn't really understand how layout is related to the index_page query, which generates only the basic html of the page.

Yes, that's right, the layout isn't in the index page, but it only gets refreshed during the initial load sequence, via the _dash-layout request.