PyQt5:样式表和来自 QWidget 的继承

问题描述

我的代码生成一个包含两个 QWidget 的窗口，一个红色 (wg1) 和一个蓝色 (wg2).如果它们变成继承自 QWidget 的 Fields(注释掉)，它们的颜色就会消失.

My code generates a Window containing two QWidgets, a red (wg1) and a blue (wg2) one. If they become Fields (commented out) which inherits from QWidget, their color disappears.

我的问题是:为什么 Field(继承自 QWidget)需要有一行

My question is: Why is it necessary for a Field (which inherits from QWidget), to have the line

self.setAttribute(Qt.WA_StyledBackground, True)

在它的 __init__ 方法中，而 QWidget 不需要这一行?

in its __init__-method while a QWidget doesn't need this line?

import sys
from PyQt5 import QtWidgets
from PyQt5.QtWidgets import QWidget, QApplication, QGridLayout
from PyQt5.QtCore import Qt

class Field(QWidget):
    def __init__(self, name):
        super().__init__()
        self.name = name
        # self.setAttribute(Qt.WA_StyledBackground, True)# !!!
        
    def mousePressEvent(self, event):
        print(f" click makes {self.name} green")
        self.setStyleSheet("background: #00ff00;")

if __name__ == "__main__":
    app = QApplication(sys.argv)
    root = QWidget()
    grid = QGridLayout()
    root.setLayout(grid)
    root.resize(300,100)

    wg1 = QWidget()
    wg2 = QWidget()
    # wg1 = Field('wg1')
    # wg2 = Field('wg2')

    wg1.setStyleSheet("background: #aa1111;")
    grid.addWidget(wg1, 0, 0)

    wg2.setStyleSheet("background: #1111aa;")
    grid.addWidget(wg2, 0, 2)

    root.show()
    sys.exit(app.exec_())

推荐答案

解释在样式表参考中与 QWidget 相关的部分:

如果您从 QWidget 继承，您需要为您的自定义 QWidget 提供一个paintEvent，如下所示:

If you subclass from QWidget, you need to provide a paintEvent for your custom QWidget as below:

默认情况下，QWidget 会默认执行此操作，但 QWidget 子类不会，因此您要么设置标志，要么实现paintEvent.

By default, QWidget does that by default, but QWidget subclasses do not, so you either set the flag or you implement the paintEvent.

无论如何，请考虑使用 样式表选择器 并避免通用/通用语法，因为它们通常会导致复杂的子小部件出现意外行为.

In any case, consider using stylesheet selectors and avoid generic/universal syntax as they often result in unexpected behavior for complex child widgets.

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