title: Problems with matplotlib and PyQt5
body: <p>Im currently working on a HDF5 converting and viewing tool. I tried to plot some measurement data from the HDF5 files in my TabWidget. The problem is, that the plots wont appear before i minimize the window. 
  Thats the code of the main window:</p>
  
  <pre><code># Plot
  self.plot = plt
  self.figure = self.plot.figure(figsize=(10, 10))
  self.plotLayout = QtWidgets.QVBoxLayout()
  self.canvas = FigureCanvas(self.figure)
  self.plotLayout.addWidget(self.canvas)
  self.ax = self.figure.add_subplot(111)
  
  self.tabWidget = QtWidgets.QTabWidget(self.centralwidget)
  
  # Never change the object name of a tab!
  self.tab = QtWidgets.QWidget()
  self.tab.setObjectName("Table")
  self.tab.layout = QtWidgets.QVBoxLayout(self)
  self.tab.setLayout(self.tab.layout)
  self.tab.layout.addWidget(self.tableWidget_1)
  self.tabWidget.addTab(self.tab, "")
  
  self.tab_1 = QtWidgets.QWidget()
  self.tab_1.setObjectName("Plot")
  self.tab_1.layout = QtWidgets.QVBoxLayout(self)
  self.tab_1.setLayout(self.plotLayout)
  self.tabWidget.addTab(self.tab_1, "")
  </code></pre>
  
  <p>The plots are defined in other files/functions. For example:</p>
  
  <pre><code>def plotData(view, path, root):
      hdf = pd.HDFStore(root)
      df = hdf.get(path)
      view.plot.xlabel("Angle")
      view.plot.ylabel("Intensity")
      view.ax = view.figure.add_subplot(111)
      view.ax.plot(df["Angle"].values, df["Intensity"].values)
      hdf.close()
  </code></pre>