问题：label要多行显示，按照这样子设置，iOS9以上work，iOS8无用
self.bookNameLabel.lineBreakMode = NSLineBreakByCharWrapping; self.bookNameLabel.numberOfLines = 0; self.bookNameLabel.textAlignment = NSTextAlignmentCenter;
然后据说要加 sizeToFit：好吧，依然然并卵
然后据说要同时加font，好吧，多行出来了，但是不居中
然后stackOverFlow：https://stackoverflow.com/questions/28579776/nstextalignmentcenter-for-uilabel-not-working/35066864#35066864?newreg=725179871da349d698d31b72bdbb3565
work！
最终：
self.bookNameLabel.font =[UIFont systemFontOfSize:18]; self.bookNameLabel.lineBreakMode = NSLineBreakByCharWrapping; self.bookNameLabel.numberOfLines = 0; self.bookNameLabel.textAlignment = NSTextAlignmentCenter; [self.bookNameLabel sizeToFit]; self.bookNameLabel.frame = CGRectMake((self.frame.size.width-self.bookNameLabel.frame.size.width)/2, self.bookNameLabel.frame.origin.y, self.bookNameLabel.frame.size.width, self.bookNameLabel.frame.size.height);
label同时设置sizeToFit，NSTextAlignmentCenter不起作用
原文：http://www.cnblogs.com/lucky-star-star/p/5854821.html