如何消除QGraphicsView不必要的水平滚动条，将垂直滚动条移至外侧？

我用PyQt6开发的应用包含一个QGraphicsView，当窗口调整到足够宽、本应无需水平滚动条时，垂直滚动条仍占用视图内部空间，导致出现仅能滚动垂直滚动条宽度的多余水平滚动条。希望垂直滚动条能显示在视图右侧的富余空间中，避免这个不必要的水平滚动条（类似QScrollArea.setWidgetResizable(True)的效果，但QGraphicsView继承自QAbstractScrollArea，没有该属性）。

最小可复现示例 #

from PyQt6 import QtCore, QtGui, QtWidgets

class MyBottomWidget(QtWidgets.QWidget):
    def __init__(self):
        super().__init__()

        scene = QtWidgets.QGraphicsScene()
        rect = QtCore.QRect(0, 0, 700, 700)
        shape = scene.addEllipse(rect)
        shape.setBrush(QtGui.QColor(QtGui.QColorConstants.Blue))
        view = QtWidgets.QGraphicsView(scene)
        view.setSceneRect(rect)
        view.setFrameShape(QtWidgets.QFrame.Shape.NoFrame)

        layout = QtWidgets.QGridLayout(self)
        self.setLayout(layout)
        layout.addWidget(view, 0, 0, QtCore.Qt.AlignmentFlag.AlignLeft | QtCore.Qt.AlignmentFlag.AlignTop)

app = QtWidgets.QApplication([])

window = QtWidgets.QMainWindow()
window.resize(800, 600)
window.setCentralWidget(MyBottomWidget())
window.show()

app.exec()

核心思路是让QGraphicsView在计算空间需求时，提前考虑垂直滚动条的宽度，避免它挤压场景的水平空间。以下两种方法均可实现：

方法1：自定义QGraphicsView子类重写尺寸提示 #

通过重写sizeHint和minimumSizeHint，给水平方向预留出垂直滚动条的宽度：

from PyQt6 import QtCore, QtGui, QtWidgets

class ResizableGraphicsView(QtWidgets.QGraphicsView):
    def sizeHint(self):
        hint = super().sizeHint()
        # 给宽度加上垂直滚动条的预估宽度
        hint.setWidth(hint.width() + self.verticalScrollBar().sizeHint().width())
        return hint

    def minimumSizeHint(self):
        hint = super().minimumSizeHint()
        hint.setWidth(hint.width() + self.verticalScrollBar().sizeHint().width())
        return hint

class MyBottomWidget(QtWidgets.QWidget):
    def __init__(self):
        super().__init__()

        scene = QtWidgets.QGraphicsScene()
        rect = QtCore.QRect(0, 0, 700, 700)
        shape = scene.addEllipse(rect)
        shape.setBrush(QtGui.QColor(QtGui.QColorConstants.Blue))
        # 使用自定义的视图类
        view = ResizableGraphicsView(scene)
        view.setSceneRect(rect)
        view.setFrameShape(QtWidgets.QFrame.Shape.NoFrame)

        layout = QtWidgets.QGridLayout(self)
        self.setLayout(layout)
        layout.addWidget(view, 0, 0, QtCore.Qt.AlignmentFlag.AlignLeft | QtCore.Qt.AlignmentFlag.AlignTop)

app = QtWidgets.QApplication([])

window = QtWidgets.QMainWindow()
window.resize(800, 600)
window.setCentralWidget(MyBottomWidget())
window.show()

app.exec()

方法2：动态调整视口边距 #

监听视图尺寸变化，根据可用空间动态设置视口边距，让垂直滚动条在空间充足时显示在视图外侧：

from PyQt6 import QtCore, QtGui, QtWidgets

class MyBottomWidget(QtWidgets.QWidget):
    def __init__(self):
        super().__init__()

        scene = QtWidgets.QGraphicsScene()
        rect = QtCore.QRect(0, 0, 700, 700)
        shape = scene.addEllipse(rect)
        shape.setBrush(QtGui.QColor(QtGui.QColorConstants.Blue))
        self.view = QtWidgets.QGraphicsView(scene)
        self.view.setSceneRect(rect)
        self.view.setFrameShape(QtWidgets.QFrame.Shape.NoFrame)
        # 设置滚动条按需显示策略
        self.view.setVerticalScrollBarPolicy(QtCore.Qt.ScrollBarPolicy.ScrollBarAsNeeded)
        self.view.setHorizontalScrollBarPolicy(QtCore.Qt.ScrollBarPolicy.ScrollBarAsNeeded)

        layout = QtWidgets.QGridLayout(self)
        self.setLayout(layout)
        layout.addWidget(self.view, 0, 0, QtCore.Qt.AlignmentFlag.AlignLeft | QtCore.Qt.AlignmentFlag.AlignTop)

        # 重写视图的resizeEvent
        self.view.resizeEvent = self.on_view_resize

    def on_view_resize(self, event):
        super(QtWidgets.QGraphicsView, self.view).resizeEvent(event)
        vsb_width = self.view.verticalScrollBar().sizeHint().width()
        # 判断视图宽度是否能容纳场景宽度+滚动条宽度
        if self.view.width() >= self.view.sceneRect().width() + vsb_width:
            # 空间充足，滚动条放在外侧，无需预留边距
            self.view.setViewportMargins(0, 0, 0, 0)
        else:
            # 空间不足，给右侧预留滚动条宽度
            self.view.setViewportMargins(0, 0, vsb_width, 0)

app = QtWidgets.QApplication([])

window = QtWidgets.QMainWindow()
window.resize(800, 600)
window.setCentralWidget(MyBottomWidget())
window.show()

app.exec()

QGraphicsView默认将滚动条的空间算在视口内部，当场景宽度接近视图宽度时，垂直滚动条的出现会挤压视口，导致需要水平滚动。通过提前预留滚动条宽度或动态调整视口边距，让滚动条不占用场景的显示空间，就能消除不必要的水平滚动条。

内容的提问来源于stack exchange，提问作者thecommexokid