import sys
from PySide.QtCore import QTimeLine
from PySide.QtGui import *

class PageA( QWidget ):
    def __init__( self ):
        super( PageA, self ).__init__()
        self.setLayout( QVBoxLayout() )
        self.btn = QPushButton( 'Calendar Page')
        self.layout().addWidget(QCalendarWidget())
        self.layout().addWidget( self.btn )

class PageB( QWidget ):
    def __init__( self ):
        super( PageB, self ).__init__()
        self.setLayout( QVBoxLayout() )
        editor = QTextEdit()
        editor.setPlainText("Hello world! "*100)
        self.btn = QPushButton( 'Text Page')
        self.layout().addWidget( editor )
        self.layout().addWidget( self.btn )

class FaderWidget( QWidget ):

    def __init__(self, old_widget, new_widget):

        QWidget.__init__( self, new_widget )
        self.old_pixmap = QPixmap( new_widget.size() )
        old_widget.render( self.old_pixmap )
        self.pixmap_opacity = 1.0

        self.timeline = QTimeLine()
        self.timeline.valueChanged.connect( self.animate )
        self.timeline.finished.connect( self.close )
        self.timeline.setDuration( 800 )
        self.timeline.start()

        self.resize( new_widget.size() )
        self.show()

    def paintEvent(self, event):

        painter = QPainter()
        painter.begin( self )
        painter.setOpacity( self.pixmap_opacity )
        painter.drawPixmap( 0, 0, self.old_pixmap )
        painter.end()

    def animate(self, value):
        print value
        self.pixmap_opacity = 1.0 - value
        self.repaint()

class StackedWidget(QStackedWidget):

    def __init__(self, parent = None):
        QStackedWidget.__init__(self, parent)

    def setCurrentIndex(self, index):
        self.fader_widget = FaderWidget(self.currentWidget(), self.widget(index))
        QStackedWidget.setCurrentIndex(self, index)

    def setPage1(self):
        self.setCurrentIndex(0)

    def setPage2(self):
        self.setCurrentIndex(1)


if __name__ == "__main__":

    app = QApplication(sys.argv)

    window = QWidget()

    stack = StackedWidget()
    pageA = PageA()
    pageB = PageB()
    stack.addWidget( pageA )
    stack.addWidget( pageB )
    #stack.addWidget(QCalendarWidget())
    #editor = QTextEdit()
    #editor.setPlainText("Hello world! "*100)

    page1Button = QPushButton("Page 1")
    page2Button = QPushButton("Page 2")

    # THOSE BUTTONS WORK:
    page1Button.clicked.connect( stack.setPage1 )
    page2Button.clicked.connect( stack.setPage2 )
    # THOSE DON'T:
    pageA.btn.clicked.connect( stack.setPage1 )
    pageB.btn.clicked.connect( stack.setPage2 )


    layout = QGridLayout(window)
    layout.addWidget(stack, 0, 0, 1, 2)
    layout.addWidget(page1Button, 1, 0)
    layout.addWidget(page2Button, 1, 1)

    window.show()

    sys.exit(app.exec_())