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];