UIFont *font = [UIFont systemFontOfSize:12];
// 根据字体得到NSString的尺寸
CGSize size = [orderStatusStr sizeWithAttributes:[NSDictionary dictionaryWithObjectsAndKeys:font,NSFontAttributeName, nil]];
根据宽度label自适应宽度,设置字体大小
_carLabel.adjustsFontSizeToFitWidth = YES;