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using PyQt, I am trying to create an interface for which I can add or remove widget dynamically. I want to define a separate class for the widget that will be added or removed. I can't seem to be able to get the widget that I instantiate to display inside the main interface. Here is the code I am using: 

from PyQt4 import QtGui, QtCore
import sys

class Main(QtGui.QMainWindow):
    def __init__(self, parent = None):
        super(Main, self).__init__(parent)

        # central widget
        self.centralWidget = QtGui.QWidget(self)

        # main layout
        self.vLayout = QtGui.QVBoxLayout(self.centralWidget)

        # main button
        self.pButton_add = QtGui.QPushButton(self.centralWidget)
        self.pButton_add.setText('button to add other widgets')

        # scroll area
        self.scrollArea = QtGui.QScrollArea(self.centralWidget)
        self.scrollArea.setWidgetResizable(True)

        # scroll area widget contents
        self.scrollAreaWidgetContents = QtGui.QWidget(self.scrollArea)

        # scroll area widget contents - layout
        self.formLayout = QtGui.QFormLayout(self.scrollAreaWidgetContents)

        self.scrollArea.setWidget(self.scrollAreaWidgetContents)

        # add all main to the main vLayout
        self.vLayout.addWidget(self.pButton_add)
        self.vLayout.addWidget(self.scrollArea)
        # set central widget
        self.setCentralWidget(self.centralWidget)
        # connections
        self.pButton_add.clicked.connect(self.addWidget)


    def addWidget(self):
        z = Test(self.scrollAreaWidgetContents)
        count = self.formLayout.rowCount()
        self.formLayout.setWidget(count, QtGui.QFormLayout.LabelRole, z)


class Test(QtGui.QWidget):
  def __init__( self, parent):
      super(Test, self).__init__(parent)

      self.pushButton = QtGui.QPushButton(self)


app = QtGui.QApplication(sys.argv)
myWidget = Main()
myWidget.show()
app.exec_()

the thing is, when I use the below code inside my 'addWidget' method, it exactly does what I want it to do, but the the class method doesn't seem to work. 

z = QtGui.QPushButton(self.scrollAreaWidgetContents)
count = self.formLayout.rowCount())
self.formLayout.setWidget(count, QtGui.QFormLayout.LabelRole, z)

I wonder why the z = Test() is not yielding any results? Any ideas? Thanks!

boundless
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3 Answers3

20

Actually, it does work. Problem is, your Test widget has a QPushButton without any layout management. So it can't calculate its minimumSize with taking the button into consideration. When you put that widget in a layout, it just shrinks to 0 (since a QWidget has no default minimumSize) and you don't see anything.

You have two choices, either you manually manage layout and enter a needless world of pain, or you rely on layout managers. In general, you should prefer the latter.

I would re-write your script like this (Although I'm not sure why you use QFormLayout, I leave it as it is.):

from PyQt4 import QtGui, QtCore
import sys

class Main(QtGui.QMainWindow):
    def __init__(self, parent = None):
        super(Main, self).__init__(parent)

        # main button
        self.addButton = QtGui.QPushButton('button to add other widgets')
        self.addButton.clicked.connect(self.addWidget)

        # scroll area widget contents - layout
        self.scrollLayout = QtGui.QFormLayout()

        # scroll area widget contents
        self.scrollWidget = QtGui.QWidget()
        self.scrollWidget.setLayout(self.scrollLayout)

        # scroll area
        self.scrollArea = QtGui.QScrollArea()
        self.scrollArea.setWidgetResizable(True)
        self.scrollArea.setWidget(self.scrollWidget)

        # main layout
        self.mainLayout = QtGui.QVBoxLayout()

        # add all main to the main vLayout
        self.mainLayout.addWidget(self.addButton)
        self.mainLayout.addWidget(self.scrollArea)

        # central widget
        self.centralWidget = QtGui.QWidget()
        self.centralWidget.setLayout(self.mainLayout)

        # set central widget
        self.setCentralWidget(self.centralWidget)

    def addWidget(self):
        self.scrollLayout.addRow(Test())


class Test(QtGui.QWidget):
  def __init__( self, parent=None):
      super(Test, self).__init__(parent)

      self.pushButton = QtGui.QPushButton('I am in Test widget')

      layout = QtGui.QHBoxLayout()
      layout.addWidget(self.pushButton)
      self.setLayout(layout)



app = QtGui.QApplication(sys.argv)
myWidget = Main()
myWidget.show()
app.exec_()
Avaris
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    Thanks for the detailed answer! The reason I was using Form Layout was that I wanted the widgets to start appearing at the top of the scroll area and fill the empty places from there, instead of appearing at the middle and rearranging themselves as the new widgets are created. Though I am sure there are other ways to do that, formlayout seemed like an easy solution to me.. Thanks again! – boundless Dec 28 '11 at 08:43
  • @boundless: Ah, I see. My approach to that would be wrapping `scrollLayout` in another `QVBoxLayout` with a stretch of `1` added below that. That should keep things at the top. – Avaris Dec 28 '11 at 09:25
  • one another thing that I like formlayout for is, it makes it easier to have two widgets next to each other as well while keeping things at top.. Though maybe at that point, I should just use grid layout. Thanks again for the hint! – boundless Dec 28 '11 at 22:11
  • @Avaris Is there a way that I can call a .py file on button click and load it in the frame. The .py file contains few attributes and buttons. So on button click I am looking to load the file in the frame. – Valla Nov 14 '14 at 16:29
  • Thank you so much! I was trying to solve this problem for 1 week. Thank you really much. – Lixt Nov 10 '22 at 19:21
4

Here is a little change that will make the button delete itself once clicked:

from PyQt4 import QtGui, QtCore
import sys

class Main(QtGui.QMainWindow):
    def __init__(self, parent = None):
        super(Main, self).__init__(parent)

        # main button
        self.addButton = QtGui.QPushButton('button to add other widgets')
        self.addButton.clicked.connect(self.addWidget)

        # scroll area widget contents - layout
        self.scrollLayout = QtGui.QFormLayout()

        # scroll area widget contents
        self.scrollWidget = QtGui.QWidget()
        self.scrollWidget.setLayout(self.scrollLayout)

        # scroll area
        self.scrollArea = QtGui.QScrollArea()
        self.scrollArea.setWidgetResizable(True)
        self.scrollArea.setWidget(self.scrollWidget)

        # main layout
        self.mainLayout = QtGui.QVBoxLayout()

        # add all main to the main vLayout
        self.mainLayout.addWidget(self.addButton)
        self.mainLayout.addWidget(self.scrollArea)

        # central widget
        self.centralWidget = QtGui.QWidget()
        self.centralWidget.setLayout(self.mainLayout)

        # set central widget
        self.setCentralWidget(self.centralWidget)

    def addWidget(self):
        self.scrollLayout.addRow(TestButton()) 


class TestButton(QtGui.QPushButton):
  def __init__( self, parent=None):
      super(TestButton, self).__init__(parent)
      self.setText("I am in Test widget")
      self.clicked.connect(self.deleteLater)


app = QtGui.QApplication(sys.argv)
myWidget = Main()
myWidget.show()
app.exec_()

This way it shouldn't mem leak when deleted and the button can actually be used for stuff. I follow this pattern for progress bars by the dozens for downloads and chunks monitoring and it works just fine even with threading and multi processing. And not the easy QThreads...

ClearType3000
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2

If u want to say , delete a widget whenever a button is clicked , or during any event of ur program , use the deleteLater() method :self.yourwidget.deleteLater()

self.button.clicked.connect(delete_widget);

def delete_widget(self):
     self.widget.deleteLater();

self.widget.deleteLater();

Using the above function makes that widget dissappear from the Application

Natesh bhat
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