Declarative API for widgets

[peterbrittain]

@boxed has proposed this API for creating a more declarative model for creating widgets...

I experimented a bit with how the API could be nicer... here's from the contacts example using some tri.declarative magic:

class ContactView(Frame):
    def __init__(self, screen, model):
        super(ContactView, self).__init__(screen,
                                          screen.height * 2 // 3,
                                          screen.width * 2 // 3,
                                          hover_focus=True,
                                          can_scroll=False,
                                          title="Contact Details",
                                          reduce_cpu=True)
        # Save off the model that accesses the contacts database.
        self._model = model
        self.widget_by_name = Struct()

        layout(
            frame=self,
            fill_frame=True,
            widgets=dict(
                name=widget(Text, label="Name:"),
                address=widget(Text, label="Address:"),
                phone=widget(Text, label="Phone number:"),
                email=widget(Text, label="Email address:"),
                notes=widget(TextBox, height=Widget.FILL_FRAME, label="Notes:", as_string=True, line_wrap=True),
            ),
            grid=[
                ['name'],
                ['address'],
                ['phone'],
                ['email'],
                ['notes']
            ]
        )

        layout(
            frame=self,
            widgets=dict(
                ok=widget(Btn, on_click=self._ok),
                cancel=widget(Btn, on_click=self._cancel),
            ),
            grid=[
                ['ok', None, 'cancel']
            ]
        )

        self.fix()

where layout is:

@dispatch(
    widgets=EMPTY,
)
def layout(*, frame, widgets, grid, fill_frame=False):
    assert len(set(len(row) for row in grid)), 'All columns must be the same width'

    columns = [1 for _ in grid[0]]
    l = Layout(columns=columns, fill_frame=fill_frame)
    frame.add_layout(l)
    for row in grid:
        for i, widget_name in enumerate(row):
            if widget_name is None:
                # blank space in the layout
                continue
            widgets[widget_name].name = widget_name

            widget = widgets[widget_name]()
            l.add_widget(widget, i)
            frame.widget_by_name[widget_name] = widget

    return l

It's a big rough still, but I stopped working on it for unrelated reasons. I hope it can give you some things to think about.

Originally posted by @boxed in #24 (comment)