自定义布局管理器中的子小部件缺少调整大小事件

Question

[在PyQt5中，我正在尝试使用带有缩放标签图像的（FlowLayout）。在使用普通BoxLayout进行测试时，缩放图像本身的工作与预期的一样，并实现了缩放的方法resizeEvent(self, evt)。

但是，当我尝试将其与自定义FlowLayout一起使用时，标签图像在调整外部容器的大小时不再收到resize事件（侦听器仅在小部件创建时执行一次），因此图像无法缩放。问题可以在这里看到：

缩小后，图像被剪切：

为什么图像不再接收resizeEvent？

布局管理器的代码来自here：

# Code from Qt Docs and modified/adapted by jonB

class FlowLayout(QLayout):
    def __init__(self, parent: QWidget=None, margin: int=-1, hSpacing: int=-1, vSpacing: int=-1):
        super().__init__(parent)

        self.itemList = list()
        self.m_hSpace = hSpacing
        self.m_vSpace = vSpacing

        self.setContentsMargins(margin, margin, margin, margin)

    def __del__(self):
        # copied for consistency, not sure this is needed or ever called
        item = self.takeAt(0)
        while item:
            item = self.takeAt(0)

    def addItem(self, item: QLayoutItem):
        self.itemList.append(item)

    def horizontalSpacing(self) -> int:
        if self.m_hSpace >= 0:
            return self.m_hSpace
        else:
            return self.smartSpacing(QStyle.PM_LayoutHorizontalSpacing)

    def verticalSpacing(self) -> int:
        if self.m_vSpace >= 0:
            return self.m_vSpace
        else:
            return self.smartSpacing(QStyle.PM_LayoutVerticalSpacing)

    def count(self) -> int:
        return len(self.itemList)

    def itemAt(self, index: int) -> typing.Union[QLayoutItem, None]:
        if 0 <= index < len(self.itemList):
            return self.itemList[index]
        else:
            return None

    def takeAt(self, index: int) -> typing.Union[QLayoutItem, None]:
        if 0 <= index < len(self.itemList):
            return self.itemList.pop(index)
        else:
            return None

    def expandingDirections(self) -> Qt.Orientations:
        return Qt.Orientations(Qt.Orientation(0))

    def hasHeightForWidth(self) -> bool:
        return True

    def heightForWidth(self, width: int) -> int:
        height = self.doLayout(QRect(0, 0, width, 0), True)
        return height

    def setGeometry(self, rect: QRect) -> None:
        super().setGeometry(rect)
        self.doLayout(rect, False)

    def sizeHint(self) -> QSize:
        return self.minimumSize()

    def minimumSize(self) -> QSize:
        size = QSize()
        for item in self.itemList:
            size = size.expandedTo(item.minimumSize())

        margins = self.contentsMargins()
        size += QSize(margins.left() + margins.right(), margins.top() + margins.bottom())
        return size

    def smartSpacing(self, pm: QStyle.PixelMetric) -> int:
        parent = self.parent()
        if not parent:
            return -1
        elif parent.isWidgetType():
            return parent.style().pixelMetric(pm, None, parent)
        else:
            return parent.spacing()

    def doLayout(self, rect: QRect, testOnly: bool) -> int:
        left, top, right, bottom = self.getContentsMargins()
        effectiveRect = rect.adjusted(+left, +top, -right, -bottom)
        x = effectiveRect.x()
        y = effectiveRect.y()
        lineHeight = 0

        for item in self.itemList:
            wid = item.widget()
            spaceX = self.horizontalSpacing()
            if spaceX == -1:
                spaceX = wid.style().layoutSpacing(QSizePolicy.PushButton, QSizePolicy.PushButton, Qt.Horizontal)
            spaceY = self.verticalSpacing()
            if spaceY == -1:
                spaceY = wid.style().layoutSpacing(QSizePolicy.PushButton, QSizePolicy.PushButton, Qt.Vertical)

            nextX = x + item.sizeHint().width() + spaceX
            if nextX - spaceX > effectiveRect.right() and lineHeight > 0:
                x = effectiveRect.x()
                y = y + lineHeight + spaceY
                nextX = x + item.sizeHint().width() + spaceX
                lineHeight = 0

            if not testOnly:
                item.setGeometry(QRect(QPoint(x, y), item.sizeHint()))

            x = nextX
            lineHeight = max(lineHeight, item.sizeHint().height())

        return y + lineHeight - rect.y() + bottom

Answer 1

resizeEvent仅在调整标签大小时才在标签上调用。布局管理器FlowLayout从未调整其子级的大小。参见doLayout]中的以下行

item.setGeometry(QRect(QPoint(x, y), item.sizeHint()))
这里子级的新大小设置为item.sizeHint()，默认为item的当前大小（可以通过覆盖标签的小部件类中的sizeHint进行更改。