QCheckBox 使用本地图片的QSS样式

setStyleSheet 为以下字符串，选中，未选中，有焦点，无焦点时显示不一样的图片

QString("QCheckBox::indicator:unchecked{image:url(%1);}"
        "QCheckBox::indicator:checked{image:url(%2);}"
        "QCheckBox::indicator:unchecked:focus{image:url(%3);}"
        "QCheckBox::indicator:checked:focus{image:url(%4);}"
                                          "").arg("/unchecked.png",
                                                   "/checked.png",
                                                   "/unchecked2.png",
                                                   "/checked2.png");