python - QGraphicsScene 将选择保留在空选择框上

Question

我在QGraphicsScene内有一个QGraphicsItem集合。我试图获得按住 ctrl 键并取消选择选择选取框内的任何项目的行为。问题是按下鼠标时当前选择将被清除。我是否缺少某些东西来防止这种情况发生？

我唯一能想到的是在鼠标释放时保存当前选择，然后在下一个鼠标按下事件时恢复它。但这看起来不太优雅，所以我希望避免这种情况。

Answer 1

这给了我我正在寻找的行为。我知道这不是最有效的方法，所以请让我知道这是否仍然可以改进!

# Override double click event so it doesn't clear selection
def mouseDoubleClickEvent(self, event):
    pass

def mousePressEvent(self, event):
    QtGui.QGraphicsView.mousePressEvent(self, event)

    # Save state of mouse button and any key modifiers
    self.mouseButton = event.button()
    self.modifiers = event.modifiers()

    # If a modifier key is held, don't clear the selection!
    if self.modifiers == QtCore.Qt.SHIFT or self.modifiers == QtCore.Qt.CTRL:
        if self.lastSelection:
            for item in self.lastSelection:
                item.setSelected(True)
    else:
        self.scene().clearSelection()

def mouseMoveEvent(self, event):
    QtGui.QGraphicsView.mouseMoveEvent(self, event)

    # Only apply if the left mouse button is being held down
    if self.mouseButton == QtCore.Qt.MouseButton.LeftButton:
        # Add items to current selection if shift is held down
        if self.modifiers == QtCore.Qt.SHIFT:
            sel = set( self.lastSelection ).union( set( self.scene().selectedItems() ) )
            for item in sel:
                item.setSelected(True)
        # Remove items from current selection if ctrl is held down
        elif self.modifiers == QtCore.Qt.CTRL:
            sel = set( self.lastSelection ).union( set( self.scene().selectedItems() ) )
            dif = set( self.lastSelection ).symmetric_difference( set( self.scene().selectedItems() ) )
            for item in sel:
                selectState = not (item not in self.lastSelection or item not in dif)
                item.setSelected(selectState)

def mouseReleaseEvent(self, event):
    QtGui.QGraphicsView.mouseReleaseEvent(self, event)

    # Reset values
    self.mouseButton = None
    self.modifiers = None
    self.lastSelection = self.scene().selectedItems() # Store last selected items

现在，如果我按住ctrl，它将取消选择项目，按住shift将添加到选择中，而普通的鼠标单击将按预期清除选择。

唯一要添加的就是将 shift 和 ctrl 包含到单次鼠标单击中，但由于按住 ctrl 确实会添加并删除，那么现在就足够了。