extend vanilla sheet demo

sheetDemo.py

from vanilla import *

class SheetDemo(object):

    def __init__(self, parentWindow):
        self.w = Sheet((200, 100), parentWindow)
        self.w.myButton = Button((10, 10, -10, 20), "My Button")
        self.w.myTextBox = TextBox((10, 40, -10, 17), "My Text Box")
        self.w.closeButton = Button((10, -30, 80, 22), "Close", self.closeCallback)
        self.w.open()
    
    def closeCallback(self, sender):
        self.w.close()

class DummyWindowController(object):
    
    def __init__(self):
        
        self.w = Window((400, 50))
        self.w.openSheet = Button((10, 10, -10, 22), "Open Sheet", callback=self.openSheetCallback)
        self.w.open()
    
    def openSheetCallback(self, sender):
        SheetDemo(self.w)

DummyWindowController()