kivy widget draws on root instead of widget place

as my first kivy adventures i try to print a data-graph.

my main.py looks like this.

I have to add some more details until stackoverflow lets me ask. But i think the code speaks for itself.

from kivy.app import App from kivy.uix.boxlayout import BoxLayout from kivy.uix.widget import Widget from kivy.graphics import Line, Color from kivy.properties import ListProperty import os class CamMeasureWidget(BoxLayout): def load_file(self): """Test: Datei laden und visualisieren""" try: with open("daten.bin", "rb") as f: data = f.read() self.ids.plot.data = list(data) print(f"{len(data)} Bytes geladen.") except Exception as e: print("Fehler beim Laden:", e) class BytePlot(Widget): data = ListProperty([]) # Liste von Bytes def __init__(self, **kwargs): super().__init__(**kwargs) with self.canvas: Color(0, 1, 0, 1) Line(circle=(self.width / 2, self.height / 2, 25), width=2) Line(rectangle=(0, 0, self.width, self.height), width=5) def on_data(self, instance, value): """Neuzeichnen wenn Daten geändert werden.""" self.draw_data() def draw_data(self): self.canvas.clear() if not self.data: return with self.canvas: Color(0, 1, 0) # grün width = self.width height = self.height n = len(self.data) if n == 0: return # Abstand zwischen Linien x_step = width / n for i, b in enumerate(self.data): x = i * x_step line_height = (b / 255) * height Line(points=[x, 0, x, line_height], width=1) class CamMeasureApp(App): def build(self): return CamMeasureWidget() if __name__ == '__main__': CamMeasureApp().run()

here is the kivy file

#:kivy 1.0.9 <CamMeasureWidget>: # BoxLayout: orientation: "vertical" spacing: 10 padding: 10 BytePlot: id: plot Button: text: "Start (Datei laden)" on_release: root.load_file() Button: text: "Stopp" on_release: print("Stopp gedrückt")

The green graph should be drawed in the first third, but it is drawn on background starting at lower left edge.

What is wrong here?

Screenshot

Greets from Bavaria