kCTUnderlineStyleAttributeName的文档传达了以下内容:kCTUnderlineStyleAttributeNameThestyleofunderlining,tobeappliedatrendertime,forthetexttowhichthisattributeapplies.ValuemustbeaCFNumberobject.DefaultiskCTUnderlineStyleNone.SetavalueofsomethingotherthankCTUnderlineStyleNonetodrawanunderline.Inaddition,thec