title: QWidget::setLayout: Attempting to set QLayout "" on MainWindow "", which already has a layout
body: <p>I'm making an application in PyQt4 and this is my code so far:</p>
  
  <pre><code>import sys
  from PyQt4 import QtGui, QtCore
  
  class MainWindow(QtGui.QMainWindow):
  
      def __init__(self):
          super(MainWindow, self).__init__()
          self.initUi()
  
      def initUi(self):
          self.setWindowTitle('Main Menu')
          self.setFixedSize(1200, 625)
          self.firstWidgets()
          self.show()
  
      def firstWidgets(self):
          self.vbox1 = QtGui.QVBoxLayout()
          self.task1 = QtGui.QLabel('Check 1', self)
          self.task1CB = QtGui.QCheckBox(self)
          self.hbox1 = QtGui.QHBoxLayout()
          self.hbox1.addWidget(self.task1)
          self.hbox1.addWidget(self.task1CB)
          self.vbox1.addLayout(self.hbox1)
  
          self.setLayout(self.vbox1)
  
  
  def main():
      application = QtGui.QApplication(sys.argv)
      gui = MainWindow()
      sys.exit(application.exec_())
  
  if __name__=='__main__':
      main()
  </code></pre>
  
  <p>My problem is in <code>MainWindow.firstWidgets()</code>. I try to set a layout but I get an error even though that's my first time using <code>.setLayout</code> for that form, which confuses me. </p>
  
  <blockquote>
    <p>QWidget::setLayout: Attempting to set QLayout "" on MainWindow "",
    which already has a layout</p>
  </blockquote>