Legend Example#

This example shows how to detach the legend from the chart and how to attach it back.

By default the chart draws the legend inside the same view with the chart. In some cases the user may want to draw the legend to somewhere else. To make this possible the legend can be detached from the chart. Detaching means that the chart doesn’t draw the legend or try to change its layout. The detached legend can then be drawn wherever the user wishes, for example, in a different graphics scene. The behavior of the legend can be inspected by running the legend example. In the example we use the bar series where we add or remove the bar sets. The legend reflects the changes in the series. The legend can be detached or attached back to the chart and its alignment can be modified. When the legend is detached, it can be resized and positioned freely.

Legend Screenshot
"""PySide6 port of the Legend example from Qt v5.x"""

import sys
from PySide6.QtCore import Qt, QRectF
from PySide6.QtGui import QBrush, QColor, QPainter, QPen
from PySide6.QtWidgets import (QApplication, QDoubleSpinBox,
    QFormLayout, QGridLayout, QGroupBox, QPushButton, QWidget)
from PySide6.QtCharts import QBarSeries, QBarSet, QChart, QChartView


class MainWidget(QWidget):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.chart = QChart()
        self.series = QBarSeries()

        self.main_layout = QGridLayout()
        self.button_layout = QGridLayout()
        self.font_layout = QFormLayout()

        self.font_size = QDoubleSpinBox()

        self.legend_posx = QDoubleSpinBox()
        self.legend_posy = QDoubleSpinBox()
        self.legend_width = QDoubleSpinBox()
        self.legend_height = QDoubleSpinBox()

        self.detach_legend_button = QPushButton("Toggle attached")
        self.detach_legend_button.clicked.connect(self.toggle_attached)
        self.button_layout.addWidget(self.detach_legend_button, 0, 0)

        self.add_set_button = QPushButton("add barset")
        self.add_set_button.clicked.connect(self.add_barset)
        self.button_layout.addWidget(self.add_set_button, 2, 0)

        self.remove_barset_button = QPushButton("remove barset")
        self.remove_barset_button.clicked.connect(self.remove_barset)
        self.button_layout.addWidget(self.remove_barset_button, 3, 0)

        self.align_button = QPushButton("Align (Bottom)")
        self.align_button.clicked.connect(self.set_legend_alignment)
        self.button_layout.addWidget(self.align_button, 4, 0)

        self.bold_button = QPushButton("Toggle bold")
        self.bold_button.clicked.connect(self.toggle_bold)
        self.button_layout.addWidget(self.bold_button, 8, 0)

        self.italic_button = QPushButton("Toggle italic")
        self.italic_button.clicked.connect(self.toggle_italic)
        self.button_layout.addWidget(self.italic_button, 9, 0)

        self.legend_posx.valueChanged.connect(self.update_legend_layout)
        self.legend_posy.valueChanged.connect(self.update_legend_layout)
        self.legend_width.valueChanged.connect(self.update_legend_layout)
        self.legend_height.valueChanged.connect(self.update_legend_layout)

        legend_layout = QFormLayout()
        legend_layout.addRow("HPos", self.legend_posx)
        legend_layout.addRow("VPos", self.legend_posy)
        legend_layout.addRow("Width", self.legend_width)
        legend_layout.addRow("Height", self.legend_height)

        self.legend_settings = QGroupBox("Detached legend")
        self.legend_settings.setLayout(legend_layout)
        self.button_layout.addWidget(self.legend_settings)
        self.legend_settings.setVisible(False)

        # Create chart view with the chart
        self.chart_view = QChartView(self.chart, self)

        # Create spinbox to modify font size
        self.font_size.setValue(self.chart.legend().font().pointSizeF())
        self.font_size.valueChanged.connect(self.font_size_changed)

        self.font_layout.addRow("Legend font size", self.font_size)

        # Create layout for grid and detached legend
        self.main_layout.addLayout(self.button_layout, 0, 0)
        self.main_layout.addLayout(self.font_layout, 1, 0)
        self.main_layout.addWidget(self.chart_view, 0, 1, 3, 1)
        self.setLayout(self.main_layout)

        self.create_series()

    def create_series(self):
        self.add_barset()
        self.add_barset()
        self.add_barset()
        self.add_barset()

        self.chart.addSeries(self.series)
        self.chart.setTitle("Legend detach example")
        self.chart.createDefaultAxes()

        self.chart.legend().setVisible(True)
        self.chart.legend().setAlignment(Qt.AlignBottom)

        self.chart_view.setRenderHint(QPainter.Antialiasing)

    def show_legend_spinbox(self):
        self.legend_settings.setVisible(True)
        chart_viewrect = self.chart_view.rect()

        self.legend_posx.setMinimum(0)
        self.legend_posx.setMaximum(chart_viewrect.width())
        self.legend_posx.setValue(150)

        self.legend_posy.setMinimum(0)
        self.legend_posy.setMaximum(chart_viewrect.height())
        self.legend_posy.setValue(150)

        self.legend_width.setMinimum(0)
        self.legend_width.setMaximum(chart_viewrect.width())
        self.legend_width.setValue(150)

        self.legend_height.setMinimum(0)
        self.legend_height.setMaximum(chart_viewrect.height())
        self.legend_height.setValue(75)

    def hide_legend_spinbox(self):
        self.legend_settings.setVisible(False)

    def toggle_attached(self):
        legend = self.chart.legend()
        if legend.isAttachedToChart():
            legend.detachFromChart()
            legend.setBackgroundVisible(True)
            legend.setBrush(QBrush(QColor(128, 128, 128, 128)))
            legend.setPen(QPen(QColor(192, 192, 192, 192)))

            self.show_legend_spinbox()
            self.update_legend_layout()
        else:
            legend.attachToChart()
            legend.setBackgroundVisible(False)
            self.hide_legend_spinbox()
        self.update()

    def add_barset(self):
        series_count = self.series.count()
        bar_set = QBarSet(f"set {series_count}")
        delta = series_count * 0.1
        bar_set.append([1 + delta, 2 + delta, 3 + delta, 4 + delta])
        self.series.append(bar_set)

    def remove_barset(self):
        sets = self.series.barSets()
        len_sets = len(sets)
        if len_sets > 0:
            self.series.remove(sets[len_sets - 1])

    def set_legend_alignment(self):
        button = self.sender()
        legend = self.chart.legend()
        alignment = legend.alignment()

        if alignment == Qt.AlignTop:
            legend.setAlignment(Qt.AlignLeft)
            if button:
                button.setText("Align (Left)")
        elif alignment == Qt.AlignLeft:
            legend.setAlignment(Qt.AlignBottom)
            if button:
                button.setText("Align (Bottom)")
        elif alignment == Qt.AlignBottom:
            legend.setAlignment(Qt.AlignRight)
            if button:
                button.setText("Align (Right)")
        else:
            if button:
                button.setText("Align (Top)")
            legend.setAlignment(Qt.AlignTop)

    def toggle_bold(self):
        legend = self.chart.legend()
        font = legend.font()
        font.setBold(not font.bold())
        legend.setFont(font)

    def toggle_italic(self):
        legend = self.chart.legend()
        font = legend.font()
        font.setItalic(not font.italic())
        legend.setFont(font)

    def font_size_changed(self):
        legend = self.chart.legend()
        font = legend.font()
        font_size = self.font_size.value()
        if font_size < 1:
            font_size = 1
        font.setPointSizeF(font_size)
        legend.setFont(font)

    def update_legend_layout(self):
        legend = self.chart.legend()

        rect = QRectF(self.legend_posx.value(),
            self.legend_posy.value(),
            self.legend_width.value(),
            self.legend_height.value())
        legend.setGeometry(rect)

        legend.update()


if __name__ == "__main__":
    app = QApplication(sys.argv)
    w = MainWidget()
    available_geometry = w.screen().availableGeometry()
    size = available_geometry.height() * 0.75
    w.setFixedSize(size, size)
    w.show()
    sys.exit(app.exec())