有正字断字的方法吗？像这样:NSStiring*string=@"InJune2010attheWorldWideDevelopersConference,Appleannouncedversion4ofXcodeduringtheDeveloperToolsStateoftheUnionaddress.";UILabel*label=[[UILabelalloc]init];label.text=string;如果框架UILabel变窄，则获取下一个:InJune2010attheWorldWideDevelopersCon-ference,Appleannouncedver-sio