iOS系统字体的设置使用

mark一个很久以前的问题，当时开发中UI坚持让两端用苹方简体字体Regular格式，那么怎么设置呢？首先苹方字体是iOS系统内置，不用外部导入。其次就是苹方是一个大的字体族，我们要拿到具体有哪些子字体。话不多少，上代码

1.找出所需的具体fontName

        //获取所有字体主族name
        for fontfamilyname  in UIFont.familyNames
        {
            print("family:",fontfamilyname);
            //通过字体主族名称获取所有的子集名称
            for fontName in UIFont.fontNames(forFamilyName: fontfamilyname)
            {
                print("\tfont:",fontName);
            }
            print("-------------");
        }

打印结果,只放出苹方相关的

苹方主族有 PingFang TC，PingFang HK，PingFang SC三种，具体释义就不添加了
...
family: PingFang TC
    font: PingFangTC-Regular
    font: PingFangTC-Thin
    font: PingFangTC-Medium
    font: PingFangTC-Semibold
    font: PingFangTC-Light
    font: PingFangTC-Ultralight
-------------
family: PingFang HK
    font: PingFangHK-Medium
    font: PingFangHK-Thin
    font: PingFangHK-Regular
    font: PingFangHK-Ultralight
    font: PingFangHK-Semibold
    font: PingFangHK-Light
-------------
family: PingFang SC
    font: PingFangSC-Medium
    font: PingFangSC-Semibold
    font: PingFangSC-Light
    font: PingFangSC-Ultralight
    font: PingFangSC-Regular//UI要求的fontName
    font: PingFangSC-Thin
-------------
...

2.设置字体 ps:这里要设置的默认字体根据项目需求是否有需要设置，PingFangSC字体是iOS9.0以后才有的，当时的项目要兼容到iOS7.0

//需要设置的地方直接调用
    func setFontWithSize(_ size:CGFloat)->UIFont?{
        let font : UIFont? = UIFont(name: "PingFangSC-Regular", size: size) ?? UIFont(name: "HelveticaNeue-Regular", size: size)
        return font
    }