仅在释放时使用 RubberBandDrag 选择项目

Question

我有一个 QGraphicsScene，我有 QGraphicsItems 并启用了 RubberBand 选择。 我想通过橡皮筋选择来选择这些项目，但我希望它们仅在释放橡皮筋时才被选中。现在它可以实时选择/取消选择项目。因此，只有在我松开橡皮筋时才能选择项目。我想我可能需要彻底改变添加橡皮筋的方式，但我不太清楚如何。

ui_path = "C:/Users/User/ui/button_test.ui"

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

        loader = QtUiTools.QUiLoader()
        self.ui = loader.load(ui_path, self)

        self.scene = QtWidgets.QGraphicsScene()
        self.ui.graphics_view.setScene(self.scene)

        self.ui.create_rect.clicked.connect(self.itemAdd) # create_rect is a QPushButton
    
        self.ui.graphics_view.setDragMode(QGraphicsView.RubberBandDrag)

        self.setWindowFlags(QtCore.Qt.Window | QtCore.Qt.CustomizeWindowHint | Qt.WindowStaysOnTopHint)

    def itemAdd(self, event):
        
        pen = QPen(Qt.GlobalColor.lightGray)
        pen.setWidth(10)

        brush = QBrush(Qt.GlobalColor.lightGray)

        rect = self.scene.addRect(0, 0, 40, 40, pen, brush)
      
        rect.setFlag(QGraphicsItem.ItemIsMovable)
        rect.setFlag(QGraphicsItem.ItemIsFocusable)
        rect.setFlag(QGraphicsItem.ItemIsSelectable)
        


if __name__ == '__main__':
    win = Test()
    win.ui.show()

我还想让我的橡皮筋区域着色和半透明。 我已阅读文档，但无法正确实现我已阅读的所有内容。任何帮助将不胜感激！

Answer 1

一种可能的解决方案是创建一个“假”橡皮筋，它是视图（或者，更好的是，视口）的子小部件。

虽然 QGraphicsView 在paintEvent 中执行此操作（在视图上绘制“虚拟”矩形），但使用子小部件可避免覆盖绘制事件并提供对其行为的更多控制。

class Test(QWidget):
    def __init__(self):
        # ...
        self.ui.graphics_view.viewport().installEventFilter(self)
        self.rubberBand = None

    def eventFilter(self, obj, event):
        if event.type() == event.MouseButtonPress and event.button() == Qt.LeftButton:
            # if there is no item at the mouse position, create a rubber band
            if not self.ui.graphics_view.itemAt(event.pos()) and not self.rubberBand:
                self.createRubberBand(event.pos())
        elif event.type() == event.MouseMove and self.rubberBand:
            self.updateRubberBand(event.pos())
        elif event.type() == event.MouseButtonRelease and self.rubberBand:
            self.finalizeRubberBand()
        return super().eventFilter(obj, event)

    def createRubberBand(self, pos):
        # create a rubber band as child widget of the *viewport*
        self.rubberBand = QWidget(self.ui.graphics_view.viewport())
        # store the start position to get the proper rectangle when dragging
        self.rubberBand.start = pos

        # use the palette to get the default selection color and
        # make it semi transparent for the background
        background = self.palette().color(QPalette.Highlight)
        background.setAlphaF(.5)
        self.rubberBand.setStyleSheet('''
            border: 1px solid palette(highlight); 
            background: {};
        '''.format(background.name(background.HexArgb)))

        self.rubberBand.setGeometry(pos.x(), pos.y(), 0, 0)
        self.rubberBand.show()

    def updateRubberBand(self, pos):
        # update the rectangle based on start and mouse position, since the result
        # could be a rectangle with negative width or height, we need to "normalize"
        # as widget geometries can only have positive dimensions
        rect = QRect(self.rubberBand.start, pos).normalized()
        self.rubberBand.setGeometry(rect)

    def finalizeRubberBand(self):
        # map the geometry of the rubber band to the scene
        area = self.ui.graphics_view.mapToScene(self.rubberBand.geometry())
        path = QPainterPath()
        path.addPolygon(area)
        self.scene.setSelectionArea(path)
        # remove the rubber band
        self.rubberBand.deleteLater()
        self.rubberBand = None