在 PyQt5 中从 QGraphicsScene 中选择项目

Question

我正在使用 QGraphicsView 和 QGraphicsSCene 加载图像。我在 QGraphicsScene 中有多个 RectItems。代码如下；

def load_image(self,image_item):
    rect_list = [[20,30,70,35],[50,100,60,100],[410,450,60,100]]
    self.pic = QPixmap(str(image_item.text()))
    self.scene = QGraphicsScene(self.centralWidget)
    self.brush = QBrush(Qt.BDiagPattern)
    self.pen = QPen(Qt.red)
    self.pen.setWidth(2)
    self.load_view = self.scene.addItem(QGraphicsPixmapItem(self.pic))
    for rect in rect_list:
        self.rect_item = self.scene.addRect(rect[0],rect[1],rect[2],rect[3],self.pen,self.brush) # x,y,w,h
        self.rect_item.setFlag(QGraphicsItem.ItemIsSelectable) #Item is Selectable
        self.rect_item.setFlag(QGraphicsItem.ItemIsMovable) # Item is Movable

    self.gView.setScene(self.scene)
    self.gView.setRenderHint(QPainter.Antialiasing)
    self.gView.show()

现在，每当我从 QgraphicsScene 的项目列表中单击一个 rect_item 时，我都想打印该项目。

Answer 1

我认为最简单的解决方案，如果你真的只需要一个 "item clicked" 消息，就是向项目添加 Qt.ItemIsFocusable 标志，然后使用场景的 focusItemChanged 信号：

    def load_image(self, image_item):
        # ...
        self.scene = QGraphicsScene(self.centralWidget)
        self.scene.focusItemChanged.connect(self.focusChanged)
        # ...
        for rect in rect_list:
            self.rect_item = self.scene.addRect(rect[0],rect[1],rect[2],rect[3],self.pen,self.brush) # x,y,w,h
            self.rect_item.setFlag(QGraphicsItem.ItemIsSelectable)
            self.rect_item.setFlag(QGraphicsItem.ItemIsMovable)
            # required for focusItemChanged signal to work:
            self.rect_item.setFlag(QGraphicsItem.ItemIsFocusable)

    def focusItemChanged(self, newItem, oldItem, reason):
        if newItem and reason == Qt.MouseFocusReason:
            print('item {} clicked!'.format(newItem))

不过，此方法存在一些问题，最重要的是，如果某个项目已被选中（因此它具有焦点），您将不会收到信号。

没有直接的解决方案，因为基本的 QGraphicsItems 不是 QObject 的后代，这意味着它们不能发出任何信号。

如果你不需要signal/slot支持，你可以继承QGraphicsRectItem并重新实现它的mousePressEvent:

class ClickableGraphicsRectItem(QGraphicsRectItem):
    def __init__(self, x, y, w, h, pen, brush):
        super(ClickableGraphicsRectItem, self).__init__(x, y, w, h)
        self.setPen(pen)
        self.setBrush(brush)
        # flags can be set all at once using the "|" binary operator
        self.setFlags(self.ItemIsSelectable|self.ItemIsMovable)

    def mousePressEvent(self, event):
        super(ClickableGraphicsRectItem, self).mousePressEvent(event)
        if event.button() == Qt.LeftButton:
            print('item clicked!')

class MyProgram(QMainWindow):
    def load_image(self, image_item):
        # ...
        for rect in rect_list:
            self.rect_item = ClickableGraphicsRectItem(...)

如果您确实需要一些signal/slot机制，您也可以将场景子类化并使项目发出信号。这不是最佳做法，但它有效:-)

class ClickableGraphicsRectItem(QGraphicsRectItem):
    # ...
    def mousePressEvent(self, event):
        super(ClickableGraphicsRectItem, self).mousePressEvent(event)
        if event.button() == Qt.LeftButton:
            self.scene().itemClicked.emit(self)

class ItemClickableGraphicsScene(QGraphicsScene):
    itemClicked = pyqtSignal(QGraphicsItem)

class MyProgram(QMainWindow):
    def load_image(self, image_item):
        # ...
        self.scene = ItemClickableGraphicsScene(self.centralWidget)
        self.scene.itemClicked.connect(self.itemClicked)
        # ...
        for rect in rect_list:
            self.rect_item = ClickableGraphicsRectItem(...)

    def itemClicked(self, item):
        print('item {} clicked!'.format(item))

或者，您可以重新实现图形视图的 mousePressEvent。在这个例子中，我只是检查它是否是 QGraphicsRectItem（因为您也有 QGraphicsPixmapItem），但是如果您添加其他项目类型，您将不得不更仔细地找到一种方法 "recognize" 它们。

class ClickableItemView(QGraphicsView):
    def mousePressEvent(self, event):
        super(ClickableItemView, self).mousePressEvent(event)
        if event.button() == Qt.LeftButton:
            item = self.itemAt(event.pos())
            if isinstance(item, QGraphicsRectItem):
                print('item {} clicked!'.format(item))

在 PyQt5 中从 QGraphicsScene 中选择项目

Selecting item from QGraphicsScene in PyQt5

python

pyqt

qgraphicsview

qgraphicsscene