iOSCanvas.Paint
From Xojo Documentation
Event
Called when the Canvas needs to update its graphical display.
Sample Code
To draw a blue rectangle in the Canvas:
g.FillColor = Color.RGB(0, 0, 255)
g.FillRect(0, 0, g.Width, g.Height)
g.FillRect(0, 0, g.Width, g.Height)