How to plot a bar chart with Qt Designer graphics view

[Matthew Martin]

Hello,

What is the way I can plot a bar chart in a graphics view created with Qt Designer?

Following an example I found, I tried the following without success.  The variable gv_spec is a graphics view item promoted to a PlotWidget in Designer.

curve2 = self.gv_spec.plot()
y1 = np.linspace(0, np.floor(x_time[-1]/fs), data2.shape[0])
bg1 = pg.BarGraphItem(x=data2, height=y1, width=0.6, brush='r')
curve2.addItem(bg1)

This yields the error:  AttributeError: 'PlotDataItem' object has no attribute 'addItem'

My goal is simply to change from a line graph to a bar chart.  This line that I was using works fine in displaying the line graph.

curve2 = self.gv_spec.plot(data2, clickable=True,
                           fillBrush=pg.mkBrush(0, 255, 0, 100), fillLevel=0)

How can I convert this line graph to a bar chart?

[Patrick]

Hi,

The plot() method from PlotWidget is just a convenience method to generate a PlotDataItem (which is the default scatter/line plot) and add it to the PlotItem contained within. Here you are manually creating a plot type, which then needs to be added to the scene manually (in the same way you could also construct the PlotDataItem manually and add it). So try self.gv_spec.addItem(bg1) and that should do what you want.

Patrick

[Jim Crowell]

I worked out a method that didn't require promoting, which I found very fiddly; you just add a QWidget in designer and pass to this function:

def add_plot(widget):
    """Add a plot item (that will behave nicely) to a basic QWidget (e.g.
    generated by QTDesigner).

    widget: QWidget

    returns None
    """

    layout = QtGui.QHBoxLayout()
    widget.setLayout(layout)
    layout.setSpacing(0)

    widget.plotView = pg.GraphicsView()
    layout.addWidget(widget.plotView)

    widget.plotItem = pg.PlotItem()
    widget.plotItem.resize = widget.resize
    widget.plotView.setCentralItem(widget.plotItem)