如何在 pyqt 中使用动画实现平滑滚动的 QScrollArea

前言

在之前的博客《如何在 pyqt 中实现平滑滚动的 QScrollArea》中，我们使用定时器和队列实现了平滑滚动。但是实现代码还是有一点复杂，所以这篇博客将使用 Qt 的动画框架 QPropertyAnimation 来实现相同的功能。

实现过程

SmoothScrollBar

滚动过程其实就是改变 QScrollBar 的 value() 的过程，Qt 自带的 QScrollArea 之所以无法平滑滚动，就是因为滚动时在 QScrollBar 的两个 value() 之间进行跳变。如果我们能在两个滚动值之间进行插值，就能实现平滑滚动了，这里通过重写 setValue() 函数来启动滚动动画。

class SmoothScrollBar(QScrollBar):
    """ Smooth scroll bar """

    scrollFinished = pyqtSignal()

    def __init__(self, parent=None):
        QScrollBar.__init__(self, parent)
        self.ani = QPropertyAnimation()
        self.ani.setTargetObject(self)
        self.ani.setPropertyName(b"value")
        self.ani.setEasingCurve(QEasingCurve.OutCubic)
        self.ani.setDuration(500)
        self.__value = self.value()
        self.ani.finished.connect(self.scrollFinished)

    def setValue(self, value: int):
        if value == self.value():
            return

        # stop running animation
        self.ani.stop()
        self.scrollFinished.emit()

        self.ani.setStartValue(self.value())
        self.ani.setEndValue(value)
        self.ani.start()

    def scrollValue(self, value: int):
        """ scroll the specified distance """
        self.__value += value
        self.__value = max(self.minimum(), self.__value)
        self.__value = min(self.maximum(), self.__value)
        self.setValue(self.__value)

    def scrollTo(self, value: int):
        """ scroll to the specified position """
        self.__value = value
        self.__value = max(self.minimum(), self.__value)
        self.__value = min(self.maximum(), self.__value)
        self.setValue(self.__value)

    def resetValue(self, value):
        self.__value = value

    def mousePressEvent(self, e):
        self.ani.stop()
        super().mousePressEvent(e)
        self.__value = self.value()

    def mouseReleaseEvent(self, e):
        self.ani.stop()
        super().mouseReleaseEvent(e)
        self.__value = self.value()

    def mouseMoveEvent(self, e):
        self.ani.stop()
        super().mouseMoveEvent(e)
        self.__value = self.value()

SmoothScrollArea

最后需要将 QScrollArea 的默认滚动条替换为平滑滚动的 SmoothScrollBar：

class SmoothScrollArea(QScrollArea):
    """ Smooth scroll area """

    def __init__(self, parent=None):
        super().__init__(parent)
        self.hScrollBar = SmoothScrollBar()
        self.vScrollBar = SmoothScrollBar()
        self.hScrollBar.setOrientation(Qt.Horizontal)
        self.vScrollBar.setOrientation(Qt.Vertical)
        self.setVerticalScrollBar(self.vScrollBar)
        self.setHorizontalScrollBar(self.hScrollBar)

    def setScrollAnimation(self, orient, duration, easing=QEasingCurve.OutCubic):
        """ set scroll animation

        Parameters
        ----------
        orient: Orient
            scroll orientation

        duration: int
            scroll duration

        easing: QEasingCurve
            animation type
        """
        bar = self.hScrollBar if orient == Qt.Horizontal else self.vScrollBar
        bar.ani.setDuration(duration)
        bar.ani.setEasingCurve(easing)

    def wheelEvent(self, e):
        if e.modifiers() == Qt.NoModifier:
            self.vScrollBar.scrollValue(-e.angleDelta().y())
        else:
            self.hScrollBar.scrollValue(-e.angleDelta().x())

测试

下面是一个简单的图片查看器测试程序：

# coding:utf-8
import sys
from PyQt5.QtCore import QEasingCurve, Qt
from PyQt5.QtGui import QPixmap
from PyQt5.QtWidgets import QApplication, QLabel


class Demo(SmoothScrollArea):

    def __init__(self):
        super().__init__()
        self.label = QLabel(self)
        self.label.setPixmap(QPixmap("shoko.jpg"))

        # customize scroll animation
        self.setScrollAnimation(Qt.Vertical, 400, QEasingCurve.OutQuint)
        self.setScrollAnimation(Qt.Horizontal, 400, QEasingCurve.OutQuint)

        self.horizontalScrollBar().setValue(1900)
        self.setWidget(self.label)
        self.resize(1200, 800)


if __name__ == '__main__':
    app = QApplication(sys.argv)
    w = Demo()
    w.show()
    app.exec_()

测试用的图片如下（硝子酱真可爱🥰：

写在最后

至此平滑滚动的实现方式就已介绍完毕了，更多自定义小部件可以参见 PyQt-Fluent-Widgets，以上~~