Graphs don't have the values after turning them into images

[Rangerguy128]

This has been a real headscratcher for a while. I’ve been working to intergrate a print function for my desktop app program where the users can print a document with the generated graphs added on it. Before I do that, I need to find a way to save the graphs as images. After many attempts, I only managed to print out images of the graphs before the data was to be added, even though I saved these images right after adding the values from a CSV file into the graph. This is what it should look like:

However, when I try to save the image, it just shows the graphs but without the values (the colored bars) Mind you, I'm using PyQt and CustomWidgets to create the graphs. Here's what I've used to create the graph in my code, as well as saving it as an image:

def create_temp_chart(self):
        if not self.fileName:
            return
        low = QtChart.QBarSet("min")
        high = QtChart.QBarSet("max")
        ltemp = []
        htemp = []

        with open(self.fileName) as csvfile:
            csvreader = csv.reader(csvfile, delimiter=',')
            header_found = False
            for row in csvreader:
                if row[0] == "MinTemp":
                    header_found = True
                    continue
                if header_found:
                    ltemp.append(float(row[0]))
                    htemp.append(float(row[1]))
                if len(ltemp) >= 12:
                    break  # Assuming only the first 12 months of data are needed

        low.append(ltemp)
        high.append(htemp)

        series = QtChart.QStackedBarSeries()
        series.append(low)
        series.append(high)

        chart = QtChart.QChart()
        chart.addSeries(series)
        chart.setTitle("Muestra de Temperatura en Celsius")
        chart.setAnimationOptions(QtChart.QChart.AnimationOption.SeriesAnimations)

        category = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"]

        axisX = QtChart.QBarCategoryAxis()
        axisX.append(category)
        axisX.setTitleText("Mes")
        chart.addAxis(axisX, Qt.AlignmentFlag.AlignBottom)
        axisY = QtChart.QValueAxis()
        axisY.setRange(-52, 52)
        axisY.setTitleText("Temperatura en Celsius")
        chart.addAxis(axisY, Qt.AlignmentFlag.AlignLeft)
        series.attachAxis(axisX)
        series.attachAxis(axisY)

        self.ui.chart_view_temp = QtChart.QChartView(chart)
        self.ui.chart_view_temp.setRenderHint(QPainter.RenderHint.Antialiasing)
        self.ui.chart_view_temp.chart().setTheme(QtChart.QChart.ChartTheme.ChartThemeDark)
        sizePolicy = QSizePolicy(QSizePolicy.Policy.Expanding, QSizePolicy.Policy.Expanding)
        sizePolicy.setHeightForWidth(self.ui.chart_view_temp.sizePolicy().hasHeightForWidth())
        self.ui.chart_view_temp.setSizePolicy(sizePolicy)

        self.ui.gridLayout_2.addWidget(self.ui.chart_view_temp)
        self.ui.frame_18.setStyleSheet(u"background-color: transparent")

        # Save chart as image
        self.save_chart_as_image(self.ui.chart_view_temp, "temp_chart.png")

def save_chart_as_image(self, chart_view, file_name):
        QApplication.processEvents()  # Process all pending events to ensure rendering is complete

        image = QImage(chart_view.size(), QImage.Format.Format_ARGB32)
        painter = QPainter(image)
        chart_view.render(painter)
        painter.end()
        image.save(file_name)

        # Display the image after saving
        self.display_image(file_name)

    def display_image(self, file_path):
        dialog = QDialog(self)
        dialog.setWindowTitle("Chart Image")
        layout = QVBoxLayout()
        label = QLabel()
        pixmap = QPixmap(file_path)
        label.setPixmap(pixmap)
        layout.addWidget(label)
        dialog.setLayout(layout)
        dialog.exec_()

Any advice on how to fix this?

[JonB]

@Rangerguy128
I know nothing about when QtCharts might or might not finishing rendering/showing, if that is required to get your saved image right, But

QApplication.processEvents()  # Process all pending events to ensure rendering is complete

This for sure is insufficient. Basically you "probably" have something wrong if you are calling processEvents().

Start by changing so that you do not call save_chart_as_image() from within the code which has just created a chart. It's not shown/rendered at this point. Call it, say, from a slot attached to a singleshot timer, which gives enough time for the graph to render properly. If that works you can look at speeding up by maybe doing it from something like a showEvent() if you don't want to use a timer.