iOS label根据显示内容自适应大小

 - (void)setupLabel {
     //准备工作
     UILabel *textLabel = [[UILabel alloc] init];
     textLabel.font = [UIFont systemFontOfSize:];
     NSString *str = @"";
     textLabel.text = str;
     textLabel.backgroundColor = [UIColor redColor];
     textLabel.numberOfLines = ;//根据最大行数需求来设置
     textLabel.lineBreakMode = NSLineBreakByTruncatingTail;
     CGSize maximumLabelSize = CGSizeMake(, );//labelsize的最大值
     //关键语句
     CGSize expectSize = [textLabel sizeThatFits:maximumLabelSize];
     //别忘了把frame给回label，如果用xib加了约束的话可以只改一个约束的值
     textLabel.frame = CGRectMake(20, 70, expectSize.width, expectSize.height);
     [self.view addSubview:textLabel];
 }