获取Webview的高度

最近一个小伙伴的公司业务逻辑上需要做在一个tableView的header上加载一个WebView的逻辑。我们在- (void)webViewDidFinishLoad:(UIWebView *)webView{ CGFloat heights = [[webView stringByEvaluatingJavaScriptFromString:@"document.body.offsetHeight"]floatValue]; NSLog(@"高度为：%f",heights); }中获取的高度确是不正常的、是无法使用的。在查阅资料后得知在：web中有很多 图片未加载完成 的话，获取的高度将小于真实高度，那在它加载完成后，内容将显示不全。我们必须换一种方式来获取的网页的真实高度。查阅后得知使用kvo能够很好的解决的这个问题。现将代码贴出以供后来者参考。当然后有更好的方案可以再评论里提出，共同进步一起提高。

代码示例：

#import "ViewController.h"
//#import "uiweb"
@interface ViewController ()<UIWebViewDelegate,UITableViewDelegate,UITableViewDataSource>{
    CGFloat webViewHeight;
}
@property(nonatomic,strong)UIWebView * webView;
@property(nonatomic,strong)UITableView * listTab;
@end

@implementation ViewController
- (UIWebView *)webView{
    if (!_webView) {
        _webView = [[UIWebView alloc]initWithFrame:self.view.frame];
    }
    return _webView;
}
- (UITableView *)listTab{
    if (!_listTab) {
        _listTab = [[UITableView alloc]init];
    }
    return _listTab;
}
- (void)viewDidLoad {
    [super viewDidLoad];
    
    [self.view addSubview:self.listTab];
    self.listTab.frame = self.view.bounds;
    self.listTab.dataSource = self;
    self.listTab.delegate = self;
    [self.listTab registerClass:[UITableViewCell class] forCellReuseIdentifier:@"ID"];
    
    [self.view addSubview: self.webView];
    NSURL *url = [NSURL URLWithString:@"http://118.178.152.151:8088/platform/news_detail.html?id=32"];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    [self.webView loadRequest:request];
    self.webView.delegate = self;
    [self.webView.scrollView addObserver:self forKeyPath:@"contentSize" options:NSKeyValueObservingOptionNew context:nil];
    self.webView.scrollView.scrollEnabled = NO;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section{
    return 5;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
    UITableViewCell * cell = [tableView dequeueReusableCellWithIdentifier:@"ID"];
    cell.backgroundColor = [UIColor redColor];
    return cell;
}
- (void)webViewDidFinishLoad:(UIWebView *)webView{

   
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    if ([keyPath isEqualToString:@"contentSize"]) {
        webViewHeight = [[self.webView stringByEvaluatingJavaScriptFromString:@"document.body.offsetHeight"] floatValue];
        CGRect newFrame       = self.webView.frame;
        newFrame.size.height  = webViewHeight;
        self.webView.frame = newFrame;
        NSLog(@"%f",self.webView.frame.size.height);
        [self.listTab setTableHeaderView:self.webView];
    }
}
-(void)viewWillDisappear:(BOOL)antimated{
    [super viewWillDisappear:antimated];
    [self.webView.scrollView removeObserver:self
                                    forKeyPath:@"contentSize" context:nil];
//也可以放在delloc方法中移除
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}


@end