自适应lable高度和长度
NSString * str = @"专题天气预报”;
CGSize size = [str sizeWithAttributes:@{NSFontAttributeName:[UIFont systemFontOfSize:36]}];
lable = [[UILabel alloc]initWithFrame:CGRectMake([[UIScreen mainScreen]bounds].size.width, 0,size.width, size.height)];
lable.text = str;
lable.font = [UIFont systemFontOfSize:36];
lable.textAlignment = NSTextAlignmentCenter
lable.backgroundColor = [UIColor greenColor];
[self.view addSubview:lable];
CGRectrect = [str boundingRectWithSize:CGSizeMake(170, 500) options:NSStringDrawingUsesFontLeading | NSStringDrawingUsesLineFragmentOrigin attributes:@{NSFontAttributeName:[UIFont systemFontOfSize:17]} context:nil];
