需求：给UIbutton设置两行文字，两行文字字体颜色各不相同。两行文字均水平居中。
Glass.png
NSMutableAttributedString *title = [[NSMutableAttributedString alloc] initWithString:[NSString stringWithFormat:@"%@\n",@"第一行文字"] attributes:@{NSFontAttributeName:[UIFont systemFontOfSize:20], NSForegroundColorAttributeName:[UIColor blueColor]}];
NSAttributedString *time = [[NSAttributedString alloc] initWithString:@"第二行" attributes:@{NSFontAttributeName:[UIFont systemFontOfSize:40],NSForegroundColorAttributeName:[UIColor blackColor]}];
[title appendAttributedString:time];
NSMutableParagraphStyle *paraStyle = [[NSMutableParagraphStyle alloc] init];
[paraStyle setLineSpacing:10];
paraStyle.alignment = NSTextAlignmentCenter;
[title addAttributes:@{NSParagraphStyleAttributeName:paraStyle} range:NSMakeRange(0, title.length)];
UIButton *btn = [[UIButton alloc] initWithFrame:CGRectMake(0, 100, 375, 300)];
btn.titleLabel.lineBreakMode = NSLineBreakByWordWrapping;
[btn setAttributedTitle:title forState:UIControlStateNormal];
NSString *string = @"之二噶山东干嘛干嘛没代沟按摩棒\n嘎嘎缴纳低昂";
NSArray *array = [string componentsSeparatedByString:@"\n"];
NSAttributedString * attString = [[NSAttributedString alloc] initWithString:@"耐烦地\n爱国迪迦奥is机动工爱的"];
NSRange range = [attString.string rangeOfString:@"\n"];
NSAttributedString *component = [attString attributedSubstringFromRange:NSMakeRange(0, range.location)];
NSString 可以根据某个特定的字符将string分割开，但是NSAttributedString没有这个方法（思维误区：NSAttributedString并不是继承自NSString。NSAttributedString有个string属性，可以获取到富文本中的字符串）。
属性字典的属性名称全部在NSAttributedString.h类中。
