Handle mouse events on both parent and child widgets (button don't consume event?)

Question

Here's my setup:

I have a eventFilter on my QTableWidget to handle both mousePress and mouseRelease events.

I also have a custom class for the QPushButton to handle mousePress and mouseRelease events.

However when I trigger the mousePress event by clicking and holding on the button, the QTableWidget doesn't see the event.

Just in case here's the code for both the custom QPushButton class and QTableWidget eventFilter.

class Button(QPushButton):
    key = None

    def __init__(self, title, parent):
        super().__init__(title, parent)

    def mousePressEvent(self, e):

        super().mousePressEvent(e)

        if e.button() == Qt.LeftButton:
            print('press')


class TableWidget(QTableWidget):

    def __init__(self, rows, columns, parent=None):
        QTableWidget.__init__(self, rows, columns, parent)
        self._last_index = QPersistentModelIndex()
        self.viewport().installEventFilter(self)

    def eventFilter(self, source, event):
        if event.type() == QEvent.MouseButtonRelease:
            print("mouse release")
        return QTableWidget.eventFilter(self, source, event)

What I'm hoping to see is when I press the custom button and then release mouse, that it will print "mouse release" in the console.

This doesn't happen.

But it does print it successfully when I click anywhere in the table except the button.

Let me know in the comments if you want me to add any extra information.

Answer 1

Explanation:

As I already pointed out in this post: The handling of mouse events between the widgets goes from children to parents, that is, if the child does not accept the event (it does not use it) then it will pass the event to the parent.. That can be verified using the following example:

from PyQt5.QtCore import Qt
from PyQt5.QtWidgets import (
    QApplication,
    QLabel,
    QPushButton,
    QTableWidget,
    QTableWidgetItem,
    QVBoxLayout,
    QWidget,
)


class TableWidget(QTableWidget):
    def mouseReleaseEvent(self, event):
        super().mouseReleaseEvent(event)
        print("released")


class Widget(QWidget):
    def __init__(self, parent=None):
        super().__init__(parent)

        self.tablewidget = TableWidget(4, 4)

        container = QWidget()
        lay = QVBoxLayout(container)
        lay.addWidget(QLabel("QLabel", alignment=Qt.AlignCenter))
        lay.addWidget(QPushButton("QPushButton"))
        container.setFixedSize(container.sizeHint())

        item = QTableWidgetItem()
        self.tablewidget.setItem(0, 0, item)
        item.setSizeHint(container.sizeHint())
        self.tablewidget.setCellWidget(0, 0, container)
        self.tablewidget.resizeRowsToContents()
        self.tablewidget.resizeColumnsToContents()

        lay = QVBoxLayout(self)
        lay.addWidget(self.tablewidget)


def main():
    import sys

    app = QApplication(sys.argv)

    widget = Widget()
    widget.resize(640, 480)
    widget.show()

    sys.exit(app.exec_())


if __name__ == "__main__":
    main()

If the QPushButton is pressed then the mouseReleaseEvent method of the QTableWidget will not be invoked because the QPushButton consumes it, unlike when the QLabel is pressed since it does not consume it and the QTableWidget does.

Solution:

As I pointed out in the other post, a possible solution is to use an eventfilter to the QWindow and to be able to filter by verifying that the click is given on a cell.

from PyQt5.QtCore import (
    pyqtSignal,
    QEvent,
    QObject,
    QPoint,
    Qt,
)
from PyQt5.QtWidgets import (
    QApplication,
    QLabel,
    QPushButton,
    QTableWidget,
    QTableWidgetItem,
    QVBoxLayout,
    QWidget,
)


class MouseObserver(QObject):
    pressed = pyqtSignal(QPoint, QPoint)
    released = pyqtSignal(QPoint, QPoint)
    moved = pyqtSignal(QPoint, QPoint)

    def __init__(self, window):
        super().__init__(window)
        self._window = window

        self.window.installEventFilter(self)

    @property
    def window(self):
        return self._window

    def eventFilter(self, obj, event):
        if self.window is obj:
            if event.type() == QEvent.MouseButtonPress:
                self.pressed.emit(event.pos(), event.globalPos())
            elif event.type() == QEvent.MouseMove:
                self.moved.emit(event.pos(), event.globalPos())
            elif event.type() == QEvent.MouseButtonRelease:
                self.released.emit(event.pos(), event.globalPos())
        return super().eventFilter(obj, event)


class Widget(QWidget):
    def __init__(self, parent=None):
        super().__init__(parent)

        self.tablewidget = QTableWidget(4, 4)

        container = QWidget()
        lay = QVBoxLayout(container)
        lay.addWidget(QLabel("QLabel", alignment=Qt.AlignCenter))
        lay.addWidget(QPushButton("QPushButton"))
        container.setFixedSize(container.sizeHint())

        item = QTableWidgetItem()
        self.tablewidget.setItem(0, 0, item)
        item.setSizeHint(container.sizeHint())
        self.tablewidget.setCellWidget(0, 0, container)
        self.tablewidget.resizeRowsToContents()
        self.tablewidget.resizeColumnsToContents()

        lay = QVBoxLayout(self)
        lay.addWidget(self.tablewidget)

    def handle_window_released(self, window_pos, global_pos):
        lp = self.tablewidget.viewport().mapFromGlobal(global_pos)
        ix = self.tablewidget.indexAt(lp)
        if ix.isValid():
            print(ix.row(), ix.column())


def main():
    import sys

    app = QApplication(sys.argv)

    widget = Widget()
    widget.resize(640, 480)
    widget.show()

    mouse_observer = MouseObserver(widget.windowHandle())
    mouse_observer.released.connect(widget.handle_window_released)

    sys.exit(app.exec_())


if __name__ == "__main__":
    main()