Changing Pixmap image automatically at runtime in PyQt

Question

I wish to change the image of a pixmap being displayed in a window automatically using a while loop that has a defined delay and uses locations of images stored in a string list. All possibilities I tried led to the first image being displayed but not changing at runtime. Any changes gets reflected only after the program has completed all kinds of execution.

from PyQt4 import QtCore, QtGui
import time
import sys

try:
    _fromUtf8 = QtCore.QString.fromUtf8
except AttributeError:
    def _fromUtf8(s):
        return s

try:
    _encoding = QtGui.QApplication.UnicodeUTF8
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig, _encoding)
except AttributeError:
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig)


class Ui_Form(QtGui.QWidget):
    def __init__(self):
        QtGui.QWidget.__init__(self)
        self.setupUi(self)
    def setupUi(self, Form):
        Form.setObjectName(_fromUtf8("Form"))
        Form.resize(598, 555)
        self.horizontalLayout = QtGui.QHBoxLayout(Form)
        self.horizontalLayout.setObjectName(_fromUtf8("horizontalLayout"))
        self.start_pulse = QtGui.QPushButton(Form)
        self.start_pulse.setObjectName(_fromUtf8("start_pulse"))
        self.horizontalLayout.addWidget(self.start_pulse)
        self.label = QtGui.QLabel(Form)
        self.label.setAutoFillBackground(True)
        self.label.setText(_fromUtf8(""))
        self.label.setPixmap(QtGui.QPixmap(_fromUtf8("GUI.png")))
        self.label.setScaledContents(True)
        self.label.setObjectName(_fromUtf8("label"))
        self.horizontalLayout.addWidget(self.label)

        self.retranslateUi(Form)
        QtCore.QMetaObject.connectSlotsByName(Form)


    def retranslateUi(self, Form):
        Form.setWindowTitle(_translate("Form", "Form", None))
        self.start_pulse.setText(_translate("Form", "start", None))
        self.start_pulse.clicked.connect(self.soumyajit)
    def soumyajit(self):
        j=0
        while(1):
            print("change")
            if j==0:
                self.label.setPixmap(QtGui.QPixmap(_fromUtf8("GUI2.png")))
            if j==1:
                self.label.setPixmap(QtGui.QPixmap(_fromUtf8("GUI.png")))
            if j==2:
                self.label.setPixmap(QtGui.QPixmap(_fromUtf8("GUI2.png")))
            if j==3:
                self.label.setPixmap(QtGui.QPixmap(_fromUtf8("GUI.png")))
            j=j+1
            #delay
            time.sleep(.5)
if __name__=='__main__':
        app=QtGui.QApplication(sys.argv)
        ex = Ui_Form()
        ex.show()
        sys.exit(app.exec_())

Answer 1

You run your loop in GUI thread so it's freeze all your app. It is bad approach. You should use QTimer instead. Use timeout() signal do all you image changes inside special slot. QTimer is asynchronous so it will not freeze your app.

You can also call processEvents() inside loop but it is not good solution, timer is better than loop with sleep.

Answer 2

Following code what I modified from your code, it works well:

Original Code from Changing Pixmap image automatically at runtime in PyQt

Modified for solving problem by WonJong Kim (wjkim@etri.re.kr)

import sys
import time
import numpy
from PyQt4 import QtCore, QtGui
import PyQt4.Qwt5 as Qwt

numPoints=1000
xs=numpy.arange(numPoints)
ys=numpy.sin(3.14159*xs*10/numPoints) #this is our data

try:
    fromUtf8 = QtCore.QString.fromUtf8

except AttributeError:
    def _fromUtf8(s):
    return s

try:
    _encoding = QtGui.QApplication.UnicodeUTF8
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig, _encoding)

except AttributeError:
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig)

class Ui_Form(QtGui.QWidget):
    def __init__(self):
        QtGui.QWidget.__init__(self)
        self.setupUi(self)
        self.index = 0

    def setupUi(self, Form):
        Form.setObjectName(_fromUtf8("Form"))
        Form.resize(500, 300)
        self.horizontalLayout = QtGui.QHBoxLayout(Form)
        self.horizontalLayout.setObjectName(_fromUtf8("horizontalLayout"))
        self.start_pulse = QtGui.QPushButton(Form)
        self.start_pulse.setObjectName(_fromUtf8("start_pulse"))
        self.stop_pulse = QtGui.QPushButton(Form)
        self.stop_pulse.setObjectName(_fromUtf8("stop_pulse"))
        self.horizontalLayout.addWidget(self.start_pulse)
        self.horizontalLayout.addWidget(self.stop_pulse)
        self.label = QtGui.QLabel(Form)
        self.label.setAutoFillBackground(True)
        self.label.setText(_fromUtf8(""))
        self.label.setPixmap(QtGui.QPixmap(_fromUtf8("GUI.png")))
        self.label.setScaledContents(True)
        self.label.setObjectName(_fromUtf8("label"))
        self.horizontalLayout.addWidget(self.label)

        self.retranslateUi(Form)
        QtCore.QMetaObject.connectSlotsByName(Form)

    def refreshUi(self):
        if self.index%10==0:
            self.label.setPixmap(QtGui.QPixmap(_fromUtf8("Images/10.jpg")))
        if self.index%10==1:
            self.label.setPixmap(QtGui.QPixmap(_fromUtf8("Images/1.jpg")))
        if self.index%10==2:
            self.label.setPixmap(QtGui.QPixmap(_fromUtf8("Images/2.jpg")))
        if self.index%10==3:
            self.label.setPixmap(QtGui.QPixmap(_fromUtf8("Images/3.jpg")))
        if self.index%10==4:
            self.label.setPixmap(QtGui.QPixmap(_fromUtf8("Images/4.jpg")))
        if self.index%10==5:
            self.label.setPixmap(QtGui.QPixmap(_fromUtf8("Images/5.jpg")))
        if self.index%10==6:
            self.label.setPixmap(QtGui.QPixmap(_fromUtf8("Images/6.jpg")))
        if self.index%10==7:
            self.label.setPixmap(QtGui.QPixmap(_fromUtf8("Images/7.jpg")))
        if self.index%10==8:
            self.label.setPixmap(QtGui.QPixmap(_fromUtf8("Images/8.jpg")))
        if self.index%10==9:
            self.label.setPixmap(QtGui.QPixmap(_fromUtf8("Images/9.jpg")))

    def retranslateUi(self, Form):
        Form.setWindowTitle(_translate("Form", "Form", None))
        self.start_pulse.setText(_translate("Form", "start", None))
        self.start_pulse.clicked.connect(self.start)
        self.stop_pulse.setText(_translate("Form", "stop", None))
        self.stop_pulse.clicked.connect(self.stop)

    def start(self):
        self.timer1.start(500.0) #set the interval (in ms)

    def stop(self):
        self.timer1.stop() #stop the timer

    def change_index(self):
        self.index += 1


if __name__ == "__main__":
    app = QtGui.QApplication(sys.argv)
    win_plot = Ui_Form()

    win_plot.index = 0
    win_plot.timer = QtCore.QTimer() #start a timer (to call replot events)
    win_plot.timer.start(100.0) #set the interval (in ms)
win_plot.connect(win_plot.timer, QtCore.SIGNAL('timeout()'), win_plot.refreshUi)

win_plot.timer1 = QtCore.QTimer() #start a timer (to call replot events)
win_plot.connect(win_plot.timer1, QtCore.SIGNAL('timeout()'),
    win_plot.change_index)

# show the main window
win_plot.show()
sys.exit(app.exec_())