Question

I’m fairly new to Python and Qt, but I’m trying to create a GUI with some animated graphic elements. I can make a simple animation work; in the following code class MyView will work when called, but class GraphicsView is not animated!

Can anyone help me see the problem?

The problem is in the class GraphicsScene, I think:

import sys
from PyQt4 import QtGui, QtCore

class MyView(QtGui.QGraphicsView):
    def __init__(self):
        QtGui.QGraphicsView.__init__(self)

        self.scene = QtGui.QGraphicsScene(self)
        self.item = QtGui.QGraphicsEllipseItem(-20, -10, 40, 20)
        self.scene.addItem(self.item)
        self.setScene(self.scene)

        # Remember to hold the references to QTimeLine and QGraphicsItemAnimation instances.
        # They are not kept anywhere, even if you invoke QTimeLine.start().
        self.tl = QtCore.QTimeLine(1000)
        self.tl.setFrameRange(0, 100)
        self.a = QtGui.QGraphicsItemAnimation()
        self.a.setItem(self.item)
        self.a.setTimeLine(self.tl)

        # Each method determining an animation state (e.g. setPosAt, setRotationAt etc.)
        # takes as a first argument a step which is a value between 0 (the beginning of the
        # animation) and 1 (the end of the animation)
        self.a.setPosAt(0, QtCore.QPointF(0, -10))
        self.a.setRotationAt(1, 360)

        self.tl.start()

#create the graphicsView which contains the graphicsScene
class GraphicsView(QtGui.QGraphicsView):
    #initialize and set dragMode and renderHints for everything inside the view
    def __init__(self, parent=None):
        super(GraphicsView, self).__init__(parent)

        #the dragMode should be changed to use the rihgt-mousebutton
        self.setDragMode(QtGui.QGraphicsView.ScrollHandDrag)

        self.setRenderHint(QtGui.QPainter.Antialiasing)
        self.setRenderHint(QtGui.QPainter.TextAntialiasing)

    #crate a zoom function for the mouse-wheel
    def wheelEvent(self, event):
        factor = 1.5 ** (event.delta() / 240.0)
        self.scale(factor, factor)

#create the GraphicsScene containing the main graphics
class GraphicsScene(QtGui.QGraphicsScene):

    def animate(self):

        self.animations = range(3)

        #move item to position(x,y) at time t
        def animate_to(item,x,y,t):

            animation = QtGui.QGraphicsItemAnimation()
            #create a timeline of 1 second
            timeline = QtCore.QTimeLine(2000)
            #number of steps in timeline (100)
            timeline.setFrameRange(0,100)
            #set position at time t
            animation.setPosAt(t, QtCore.QPointF(x,y))
            #apply this to "item"
            animation.setItem(item)
            #add timeline to the animation
            animation.setTimeLine(timeline)

            #output of this definition is "animation"
            return animation

        self.animations[0] = animate_to(self.geos[0],200,200,0.2)
        self.animations[1] = animate_to(self.geos[1],200,200,0.2)
        self.animations[2] = animate_to(self.geos[2],200,200,0.2)

        #animation.timeline().start()
        self.animator.start(2000)


    def __init__(self, parent=None):
        QtGui.QGraphicsScene.__init__(self, parent)
        #set the size of the scene
        self.setSceneRect(0,0,2000,2000)

        #self.addRect(QtCore.QRectF(800,800,200,200))

        #---create the scene-geometries ---   

        #empty list to hold the geometries
        self.geos = []

        #create stuff to add to the scene
        geo_01 = QtGui.QGraphicsEllipseItem(800,800,200,200)
        geo_02 = QtGui.QGraphicsEllipseItem(850,850,300,300)
        geo_03 = QtGui.QGraphicsEllipseItem(900,900,400,400)
        #add stuff to the scene
        self.addItem(geo_01)
        self.addItem(geo_02)
        self.addItem(geo_03)

        #put stuff into list so it can be referenced
        self.geos.append(geo_01)
        self.geos.append(geo_02)
        self.geos.append(geo_03)

        #----do the animation thing---
        self.animator = QtCore.QTimer()

        self.animator.timeout.connect(self.animate)

        self.animate()


#Create a new class which inherrits from "QtGui.QMainWindow"
class Example(QtGui.QMainWindow):

    def __init__(self):
        #The "super()"-method returns the parrent object of the example-class
        #and it's constructor is called ("__init__")
        super(Example, self).__init__()

        self.initUI()

    #create the GUI
    def initUI(self):

        """---create the buttons---"""

        #set a font for the tool-tips
        QtGui.QToolTip.setFont(QtGui.QFont('SansSerif', 10))

        #create a button and a tool-tip for the button
        btn_01 = QtGui.QPushButton('Button', self)
        btn_01.setToolTip('This is a <b>QPushButton</b> widget')
        #resize the button with a recommended size (.sizeHint())
        btn_01.resize(btn_01.sizeHint())

        #create a button and a tool-tip for the button
        btn_02 = QtGui.QPushButton('Button', self)
        btn_02.setToolTip('This is a <b>QPushButton</b> widget')
        #resize the button with a recommended size (.sizeHint())
        btn_02.resize(btn_02.sizeHint())

        """----create a layout----"""

        #create the main widget, which holds the layout
        self.main_widget = QtGui.QWidget(self)

        #create a vertical box layout to hold the buttons on the right
        vbox = QtGui.QVBoxLayout()
        vbox.addStretch(1)
        vbox.addWidget(btn_01)
        vbox.addWidget(btn_02)  

        #create horizontal box layout to hold the vbox and the main area
        hbox = QtGui.QHBoxLayout()

        #store the GraphicsScene in a variable so it is not destroyed
        self.scene = GraphicsScene()
        #add the scene to the GraphicsView
        view = GraphicsView(self.scene)

        hbox.addWidget(view)
        hbox.addStretch(1)
        hbox.addLayout(vbox)

        self.main_widget.setLayout(hbox)
        self.setCentralWidget(self.main_widget)

        #set the possition and size of the window, then set the window title
        #these methods have been inherited by the "QtGui.QWidget"-class
        self.setGeometry(100, 100, 700, 500)
        self.setWindowTitle("PatternNexus...Maybe?")
        #self.setWindowIcon(QtGui.QIcon('web.png'))

        self.show()

    def closeEvent(self, event):
        #create a messagebox to confirm quit
        # when QtGui.QWidget is closed the QtGui.QCloseEvent is generated
        # to modify its behaviour the event handler (closeEvent()) must be reinplemented

        #create a msgBox with 2 buttons
        #4th argument is the button combination
        #5th argument is the button with initial ketboard focus
        reply = QtGui.QMessageBox.question(self, 'Message',
            "Are you leaving?", QtGui.QMessageBox.Yes | 
            QtGui.QMessageBox.No, QtGui.QMessageBox.No)

        #test the return value, is "yes" the event is accepted
        if reply == QtGui.QMessageBox.Yes:
            event.accept()
        else:
            event.ignore()

def main():
    #start the application
    app = QtGui.QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())

#if this module (.py-file) is run as the main program the statement is true
#if this module is imported the statement will return false
if __name__ == '__main__':
    main()

My main references for coding this are “Rapid GUI programming with python and QT – Chapter 12”, and these links: http://lateral.netmanagers.com.ar/stories/BBS53.html, and http://www.diotavelli.net/PyQtWiki/GraphicsView_-_SimpleAnimation

Answer 1

so the answer to my question was: start the timelne by adding:
[ animation.timeLine().start() for animation in self.animations ]
in the animate definition