0.拉线引用
@property (weak, nonatomic) IBOutlet UIWebView *classDetail;
@property (strong, nonatomic) UIActivityIndicatorView *activityIndicatorView;
//滑动view的高度
@property (weak, nonatomic) IBOutlet NSLayoutConstraint *contentHigh;

1.加入代理协议
@interface CourseViewController ()<UIWebViewDelegate>{

 float _webViewHeight;
 float _loadFlag;

}

2.把webView设置代理
self.classDetail.delegate = self;

3.加入如下方法

//设置webView自动高度
#pragma mark webView代理方法
- (void)webViewDidFinishLoad:(UIWebView *)webView {
     
    [self.activityIndicatorView stopAnimating];
      //根据网页高度
      NSString * curHeight = [webView stringByEvaluatingJavaScriptFromString:@"document.body.offsetHeight;"];
      
      _webViewHeight = [curHeight floatValue];
      _contentHigh.constant = _webViewHeight + 800;
      //背景色白色
      [self.webView stringByEvaluatingJavaScriptFromString:@"document.getElementsByTagName('body')[0].style.background='#FFFFFF'"];
      [self.webView stringByEvaluatingJavaScriptFromString:@"document.getElementsByTagName('body')[0].style.webkitTextFillColor= '#939393'"];
      
      [self.tableView reloadData];
      _loadFlag += 0.5;
      if (_loadFlag == 1) {           
           [SVProgressHUD dismiss];
      }
}

- (void)webViewDidStartLoad:(UIWebView *)webView {
     
     [self.activityIndicatorView startAnimating];
}

注意 可以单独拉控件的约束来设置高度
_contentHigh.constant = _webViewHeight + 800;
还要刷新tableView
[self.tableView reloadData];

附带js语句，改变网页字体颜色和一些参数，好用啊。
//背景色白色
[self.webView stringByEvaluatingJavaScriptFromString:@"document.getElementsByTagName('body')[0].style.background='#FFFFFF'"];
//字体颜色
[self.webView
stringByEvaluatingJavaScriptFromString:@"document.getElementsByTagName('body')[0].style.webkitTextFillColor= '#939393'"];
//字体大小

[webView stringByEvaluatingJavaScriptFromString:@"document.getElementsByTagName('body')[0].style.webkitTextSizeAdjust= '330%'"];

//系统字体颜色

[webView stringByEvaluatingJavaScriptFromString:@"document.getElementsByTagName('body')[0].style.webkitTextFillColor= 'gray'"];

还有一些属性

self.myWebView.delegate =self;
    self.myWebView.opaque =NO; //不设置这个值页面背景始终是白色
    self.myWebView.backgroundColor = [UIColorclearColor];
    self.myWebView.scalesPageToFit =NO;  //禁止用户缩放页面
    self.myWebView.dataDetectorTypes =UIDataDetectorTypePhoneNumber|UIDataDetectorTypeLink;
    self.myWebView.scrollView.pagingEnabled =YES;
    self.myWebView.scrollView.contentInset =UIEdgeInsetsMake(0,0,0,0);
    self.myWebView.autoresizingMask =UIViewAutoresizingFlexibleWidth|UIViewAutoresizingFlexibleHeight;
    [self.view addSubview:self.myWebView];