How to fix a QFocusEvent behavior

Question

I'm making a widget to access and modify QGraphicsRectItem properties(scale, rotation, etc.). The main idea is to show a widget on clicking on an item. When you click on another item, this widget should be deleted and replaced by another(showing properties of another item.)

I've implemented this using QFocusEvent and unfortunately, it gives me a SIGSEGV error. I fully understand why it happens but can`t make out how to do it in another way.

Here's a python sketch:

from PySide2 import QtWidgets, QtCore, QtGui
import sys, shiboken2


class graphicsView(QtWidgets.QGraphicsView):
    def __init__(self, scene, parent=None):
        super(graphicsView, self).__init__(parent)
        self.scene = scene

        self.setScene(self.scene)

    def wheelEvent(self, event):
        factor = 1.41 ** (-event.delta() / 240)
        self.scale(factor, factor)

class boxItem(QtWidgets.QGraphicsRectItem):
    def __init__(self, parent):
        super(boxItem, self).__init__()

        self.setFlags(QtWidgets.QGraphicsItem.ItemIsSelectable
                      | QtWidgets.QGraphicsItem.ItemIsMovable
                      | QtWidgets.QGraphicsItem.ItemIsFocusable)

        self.rect = QtCore.QRectF(0, 0, 200, 200)
        self.setRect(self.rect)

        self.parent = parent


    def focusInEvent(self, event:QtGui.QFocusEvent):
        self.pBox = propBox()
        self.parent.layout.addWidget(self.pBox)
        self.pBox.r_box.setValue(self.rotation())
        self.pBox.r_box.valueChanged.connect(self.setRotationAngle)


    def focusOutEvent(self, event:QtGui.QFocusEvent):
        # Here's a shiboken(equivalent to sip in PyQt) deletes c++ object and a python wrapper
        # It works as expected but because of focusOutEvent it deletes the widget when i click on it
        # There's when the error appears.

        self.parent.layout.removeWidget(self.pBox)
        shiboken2.delete(self.pBox)

    def setRotationAngle(self, degrees):
        br = self.boundingRect()
        self.setTransformOriginPoint(QtCore.QPointF(br.width() / 2, br.height() / 2))
        self.setRotation(-degrees)
        self.update()



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

        self.layout = QtWidgets.QVBoxLayout()
        self.layout.setAlignment(QtCore.Qt.AlignTop)
        self.setLayout(self.layout)

        self.r_label = QtWidgets.QLabel("Rotation:", self)
        self.r_box = QtWidgets.QSpinBox(self)
        self.r_layout = QtWidgets.QHBoxLayout()
        self.r_layout.addWidget(self.r_label)
        self.r_layout.addWidget(self.r_box)

        self.s_label = QtWidgets.QLabel("Scale:")
        self.s_box = QtWidgets.QSpinBox(self)
        self.s_layout = QtWidgets.QHBoxLayout()
        self.s_layout.addWidget(self.s_label)
        self.s_layout.addWidget(self.s_box)

        self.layout.addLayout(self.r_layout)
        self.layout.addLayout(self.s_layout)

class mainWidget(QtWidgets.QWidget):
    def __init__(self):
        super(mainWidget, self).__init__()

        self.layout = QtWidgets.QHBoxLayout()
        self.setLayout(self.layout)

        box1 = boxItem(self)
        box1.setRotation(45)
        box2 = boxItem(self)

        self.scene = QtWidgets.QGraphicsScene(self)
        self.scene.setSceneRect(0, 0, 500, 300)
        self.scene.addItem(box1)
        self.scene.addItem(box2)

        self.view = graphicsView(self.scene)

        self.pBox = propBox(self)

        self.layout.addWidget(self.view)



if __name__ == '__main__':
    app = QtWidgets.QApplication(sys.argv)
    window = mainWidget()
    window.show()
    sys.exit(app.exec_())

user_6622587 · Answer

I have not analyzed because your program crashes so my answer will not focus on it, instead I will focus on the underlying problem.

You just have to have a PropertyBox that you hide or show when necessary. I see a problem trying to use the focusInEvent and focusOutEvent methods because when you press the PropertyBox the item will lose its focus so the PropertyBox itself will be removed (maybe this is the reason for the crash). So instead of using the focus you should use the mousePressEvent and check if there is an item where it was clicked.

Considering the above the solution is:

import random
from PySide2 import QtCore, QtGui, QtWidgets


class BoxItem(QtWidgets.QGraphicsRectItem):
    def __init__(self, parent=None):
        super(BoxItem, self).__init__(QtCore.QRectF(0, 0, 200, 200), parent)

        self.setFlags(
            QtWidgets.QGraphicsItem.ItemIsSelectable
            | QtWidgets.QGraphicsItem.ItemIsMovable
            | QtWidgets.QGraphicsItem.ItemIsFocusable
        )
        br = self.boundingRect()
        self.setTransformOriginPoint(
            QtCore.QPointF(br.width() / 2, br.height() / 2)
        )


class PropertyBox(QtWidgets.QWidget):
    rotationChanged = QtCore.Signal(float)
    scaleChanged = QtCore.Signal(float)

    def __init__(self, parent=None):
        super(PropertyBox, self).__init__(parent)
        self.m_rotation_spinbox = QtWidgets.QDoubleSpinBox(
            minimum=-360, maximum=360
        )
        self.m_rotation_spinbox.valueChanged.connect(self.rotationChanged)
        self.m_scale_spinbox = QtWidgets.QDoubleSpinBox(
            minimum=0, maximum=100, singleStep=0.1
        )
        self.m_scale_spinbox.valueChanged.connect(self.scaleChanged)

        lay = QtWidgets.QFormLayout(self)
        lay.addRow("Rotation:", self.m_rotation_spinbox)
        lay.addRow("Scale:", self.m_scale_spinbox)

    @property
    def rotation(self):
        return self.m_rotation_spinbox.value()

    @rotation.setter
    def rotation(self, value):
        self.m_rotation_spinbox.setValue(value)

    @property
    def scale(self):
        return self.m_scale_spinbox.value()

    @scale.setter
    def scale(self, value):
        self.m_scale_spinbox.setValue(value)


class GraphicsView(QtWidgets.QGraphicsView):
    currentItemChanged = QtCore.Signal(QtWidgets.QGraphicsItem)

    def mousePressEvent(self, event):
        super(GraphicsView, self).mousePressEvent(event)
        it = self.itemAt(event.pos())
        self.currentItem = it

    @property
    def currentItem(self):
        if not hasattr(self, "_currentItem"):
            self._currentItem = None
        return self._currentItem

    @currentItem.setter
    def currentItem(self, it):
        if self.currentItem != it:
            self._currentItem = it
            self.currentItemChanged.emit(it)


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

        self.m_scene = QtWidgets.QGraphicsScene()
        self.m_view = GraphicsView(self.m_scene)
        self.m_view.currentItemChanged.connect(self.onCurrentItemChanged)

        for i in range(4):
            it = BoxItem()
            self.m_scene.addItem(it)
            it.setPos(QtCore.QPointF(100 * i, 100 * i))
            it.setBrush(QtGui.QColor(*random.sample(range(255), 3)))

        self.m_property_box = PropertyBox()
        self.m_property_box.rotationChanged.connect(self.onRotationChanged)
        self.m_property_box.scaleChanged.connect(self.onScaleChanged)
        self.m_property_box.hide()

        lay = QtWidgets.QHBoxLayout(self)
        lay.addWidget(self.m_view)
        lay.addWidget(self.m_property_box)

    @QtCore.Slot(QtWidgets.QGraphicsItem)
    def onCurrentItemChanged(self, item):
        self.m_property_box.setVisible(item is not None)
        if item is not None:
            self.m_property_box.rotation = item.rotation()
            self.m_property_box.scale = item.scale()

    @QtCore.Slot(float)
    def onRotationChanged(self, rotation):
        it = self.m_view.currentItem
        if it is not None:
            it.setRotation(rotation)

    @QtCore.Slot(float)
    def onScaleChanged(self, scale):
        it = self.m_view.currentItem
        if it is not None:
            it.setScale(scale)


if __name__ == "__main__":
    import sys

    app = QtWidgets.QApplication(sys.argv)
    w = Widget()
    w.resize(640, 480)
    w.show()
    sys.exit(app.exec_())

How to fix a QFocusEvent behavior

1 Answers