QCheckBox 使用本地圖片的QSS樣式

setStyleSheet 為以下字符串，選中，未選中，有焦點，無焦點時顯示不一樣的圖片

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");