porting a fullscreen app from Tkinter to Kivy

Question

I wrote a dashboard application in Tkinter , basically a fullscreen app with a few tk.Label in a grid, updated with various information.

I now want to recode this in Kivy but I have some problems understanding the change in philosophy.

The Tkinter skeleton is

class Dashboard(object):
    def __init__(self, parent):
        self.root = parent.root
        self.timestr = tk.Label(self.root)
        self.timestr.configure(...)
(...)

I then .configure() various things (font, text tabel, etc.)

In Kivy I want to change the design by creating several FloatLayout widgets, equivelent to the tk.Label above. I have so far

from kivy.app import App
from kivy.uix.widget import Widget
from kivy.core.window import Window

class Time(Widget):
    def __init__(self):
        self.time = "xx:xx"

    def update(self):
        self.time = "9:53"

class Dashboard(Widget):
    Time()

class DashApp(App):
    def build(self):
        dash = Dashboard()
        return dash

Window.fullscreen = True
DashApp().run()

with the relavant kv file:

#:kivy 1.8.0
<Time>:
    size: root.width, root.height / 4
    pos: 0, 0
    Label:
        center_x: self.width / 2
        top: self.top - 5
        font_size: 70
        text: "aaa"

Upon launching the app it goes fullscreen but is empty.

How should I express the fact that I want to instantiate a Dashboad() and then within it some widgets ( Time() for instance)?

Answer 1

class Dashboard(Widget):
    Time()

I think you have a misconception about what this does - that being, nothing. The Time object is instantiated but not added to the Dashboard or anything. That's why your app is blank, it's just a Dashboard widget that is itself blank.

You instead need to add the Time widget to the dashboard, eg in the __init__ :

class Dashboard(Widget):
    def __init__(self, **kwargs):
        super(Dashboard, self).__init__(**kwargs)
        self.add_widget(Time())

Since you always want to do this, it's even easier and better to do it with a kv rule:

<DashBoard>:
    Time:

You'll also have some messed up positioning right now, but it looks like you're still experimenting with that.

Answer 2

Instead of the Label center_x being self.width/2 , which I think refers to the label itself, try root.width/2 , which I believe refers to the root widget, in this case, Time .

I'm quite sure, that in the kv file, root generally refers to the widget between these <> (that is the root parent of whatever you are tweaking at the time), self refers to the current widget, and app refers to the app instance.