// 一、設置全局字體（系統庫字體）
QFont font("Courier", 10, QFont::Normal, false);
a.setFont(font);

// 二、設置全局字體（自定義字體）
int font_id = QFontDatabase::addApplicationFont(QStringLiteral(":/static/font/FormaDJRMicro-Regular.ttf"));
QString font_name = QFontDatabase::applicationFontFamilies(font_id).at(0);
QFont font_1;
font_1.setFamily(font_name);
font_1.setPixelSize(18);
a.setFont(font_1);

// 三、設置多個自定義字體（哪里需要就哪里用）
int font_id_1 = QFontDatabase::addApplicationFont(QStringLiteral(":/static/font/FormaDJRMicro-Medium.ttf"));
int font_id_2 = QFontDatabase::addApplicationFont(QStringLiteral(":/static/font/FormaDJRMicro-Regular.ttf"));

QString font_name_1 = QFontDatabase::applicationFontFamilies(font_id_1).at(0);
QString font_name_2 = QFontDatabase::applicationFontFamilies(font_id_2).at(0);

QFont font_01, font_02;
font_01.setFamily(font_name_1); font_01.setPixelSize(18);
font_02.setFamily(font_name_2); font_02.setPixelSize(18);

ui.label->setFont(font_01);
ui.pushButton->setFont(font_02);