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];

 }