PyQt5 GUI与pyqtgraph绘图不更新问题及多图添加咨询

Hey there, let's work through your PyQt5 + pyqtgraph problems together!

First up, let's figure out why your curve isn't showing up even though the axes are there. Here are the most common fixes to check:

• Verify your data is valid: Before plotting, print out your x and y arrays (e.g., print(self.x_data, self.y_data)) to make sure they're not empty, full of NaNs, or zero-length. If you're reading from serial, double-check that the data is being parsed correctly into numerical values.
• Ensure your PlotWidget is properly integrated with the UI:
  • If you used Qt Designer, did you promote a QWidget to pyqtgraph.PlotWidget? If not, you can either do that in Designer (right-click the widget > Promote to...) or manually create the PlotWidget in code and add it to your layout:

    self.plot_widget = pg.PlotWidget()
    self.your_layout_name.addWidget(self.plot_widget)  # Replace with your actual layout from Qt Designer
    

• Check your plotting logic:
  • When initializing, make sure you're creating a CurveItem and storing it (so you can update it later). For example:

    # Inside your button click slot
    self.x_data = np.linspace(0, 10, 100)
    self.y_data = np.sin(self.x_data)
    
    # First plot: create the curve
    if not hasattr(self, 'curve'):
        self.curve = self.plot_widget.plot(self.x_data, self.y_data, pen='red')
    # Subsequent updates: reuse the existing curve
    else:
        self.curve.setData(self.x_data, self.y_data)
    

• Force UI updates: Sometimes Qt needs a nudge to refresh the plot. Add self.plot_widget.repaint() or QtWidgets.QApplication.processEvents() after setting the data.
• Thread safety (if using serial): If you're reading serial data in a separate thread, never update the plot directly from the thread. Use Qt's signal-slot system to send data to the main thread, where you can safely update the curve. Example:

  # In your worker thread class
  data_ready = QtCore.pyqtSignal(np.ndarray, np.ndarray)
  
  def run(self):
      # Read serial data, parse into x and y
      self.data_ready.emit(x_data, y_data)
  
  # In your main window class
  self.thread = SerialWorker()
  self.thread.data_ready.connect(self.update_plot)
  self.thread.start()
  
  def update_plot(self, x, y):
      self.curve.setData(x, y)
  

For adding multiple plots in the same window, pyqtgraph has two great options depending on your needs:

Option 1: Use pg.GraphicsLayoutWidget (Recommended) #

This is pyqtgraph's built-in container for arranging multiple plots, and it's perfect for creating grids of plots or shared-axis layouts.

• If using Qt Designer: Promote a QWidget to pyqtgraph.GraphicsLayoutWidget, then in code:

  # Get the promoted widget from your UI
  self.graphics_layout = self.your_promoted_widget
  
  # Add first plot
  plot1 = self.graphics_layout.addPlot(title="Sine Wave")
  plot1.plot(np.linspace(0,10,100), np.sin(np.linspace(0,10,100)), pen='red')
  
  # Move to next row and add second plot
  self.graphics_layout.nextRow()
  plot2 = self.graphics_layout.addPlot(title="Cosine Wave")
  plot2.plot(np.linspace(0,10,100), np.cos(np.linspace(0,10,100)), pen='blue')
  
  # Add a plot to the right of plot2
  self.graphics_layout.nextCol()
  plot3 = self.graphics_layout.addPlot(title="Random Data")
  plot3.plot(np.random.randn(100), pen='green')
  

• You can also share axes between plots (e.g., plot2.setXLink(plot1) to sync the x-axis with plot1).

Option 2: Use Qt Layouts (Flexible Customization) #

If you need more control over plot sizes or positioning (e.g., different-sized plots), use Qt's standard layouts like QGridLayout or QHBoxLayout with individual pg.PlotWidgets:

# Create a grid layout
grid_layout = QtWidgets.QGridLayout()
self.centralwidget.setLayout(grid_layout)

# Add plots to the grid
plot1 = pg.PlotWidget(title="Plot 1")
grid_layout.addWidget(plot1, 0, 0)

plot2 = pg.PlotWidget(title="Plot 2")
grid_layout.addWidget(plot2, 0, 1)

plot3 = pg.PlotWidget(title="Plot 3")
grid_layout.addWidget(plot3, 1, 0, 1, 2)  # Span both columns

One final tip: Always avoid modifying the auto-generated code from Qt Designer directly. Instead, create a subclass that inherits from both your UI class and QMainWindow/QWidget, then set up your logic there. This makes it easier to re-generate the UI code later without losing your changes.

内容的提问来源于stack exchange，提问作者Mario Andres Gomez