一个kvo实现wkwebview加载进度条的例子（注意最后移除观察者）(代码片段)

//
//  OpenWebViewController.m
//  Treasure
//
//  Created by 蓝蓝色信子 on 16/7/29.
//  Copyright ? 2016年 GY. All rights reserved.
//

#import "ZTOpenWebViewController.h"
#import <WebKit/WebKit.h>

@interface ZTOpenWebViewController ()<WKNavigationDelegate>
//
//    //网页视图
//    UIWebView * _webView;
//
@property (strong, nonatomic) WKWebView *webView;


@property (strong, nonatomic) UIProgressView *progressView;

@end

@implementation ZTOpenWebViewController



- (void)viewDidLoad 
    [super viewDidLoad];
    //    //取消导航栏的影响
    self.automaticallyAdjustsScrollViewInsets = NO;
    self.view.backgroundColor = [UIColor whiteColor];
    
    //[SVProgressHUD show];
    //实例化
    [self createWebView];
    
    [self creatCustomProgressView];


-(void)creatCustomProgressView
    
    //增加加载进度条
    // KVO，监听webView属性值得变化(estimatedProgress,title为特定的key)
    [_webView addObserver:self forKeyPath:@"estimatedProgress" options:NSKeyValueObservingOptionNew context:nil];
    [_webView addObserver:self forKeyPath:@"title" options:NSKeyValueObservingOptionNew context:nil];
    
    // UIProgressView初始化
    self.progressView = [[UIProgressView alloc] initWithProgressViewStyle:UIProgressViewStyleDefault];
    self.progressView.frame = CGRectMake(0, 0, _webView.frame.size.width, 5);
    self.progressView.trackTintColor = [UIColor clearColor]; // 设置进度条的色彩
    self.progressView.progressTintColor = [UIColor magentaColor];
    // 设置初始的进度，防止用户进来就懵逼了（微信大概也是一开始设置的10%的默认值）
    [self.progressView setProgress:0.1 animated:YES];
    [_webView addSubview:self.progressView];


- (void)viewWillAppear:(BOOL)animated

    [self.navigationController setNavigationBarHidden:NO animated:NO];
    [super viewWillAppear:YES];

- (void)viewWillDisappear:(BOOL)animated

    [SVProgressHUD dismiss];
    [super viewWillDisappear:animated];


- (void)createWebView

    _webView = [[WKWebView alloc]initWithFrame:self.view.bounds];
    
    [self.view addSubview:_webView];
    
    //调整适应比例
    //_webView.scalesPageToFit = YES;
    //设置代理
    _webView.navigationDelegate = self;
    [[NSURLCache sharedURLCache] removeAllCachedResponses];
    [_webView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:self.urlStr] cachePolicy:NSURLRequestReloadIgnoringLocalAndRemoteCacheData timeoutInterval:10.0]];
    

#pragma mark - WKWebView NavigationDelegate

//WKNavigationDelegate
- (void)webView:(WKWebView *)webView decidePolicyForNavigationAction:(WKNavigationAction *)navigationAction decisionHandler:(void (^)(WKNavigationActionPolicy))decisionHandler 
    //NSLog(@"是否允许这个导航");
    decisionHandler(WKNavigationActionPolicyAllow);


- (void)webView:(WKWebView *)webView decidePolicyForNavigationResponse:(WKNavigationResponse *)navigationResponse decisionHandler:(void (^)(WKNavigationResponsePolicy))decisionHandler 
    //    Decides whether to allow or cancel a navigation after its response is known.
    
    //NSLog(@"知道返回内容之后，是否允许加载，允许加载");
    decisionHandler(WKNavigationResponsePolicyAllow);

- (void)webView:(WKWebView *)webView didStartProvisionalNavigation:(null_unspecified WKNavigation *)navigation 
    //NSLog(@"开始加载");
    //self.progress.alpha  = 1;
    
    //[SVProgressHUD show];
    [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
    


- (void)webView:(WKWebView *)webView didReceiveServerRedirectForProvisionalNavigation:(null_unspecified WKNavigation *)navigation 
    //NSLog(@"跳转到其他的服务器");
    


- (void)webView:(WKWebView *)webView didFailProvisionalNavigation:(null_unspecified WKNavigation *)navigation withError:(NSError *)error 
    //NSLog(@"网页由于某些原因加载失败");
    //[SVProgressHUD dismiss];
    //self.progress.alpha  = 0;
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;

- (void)webView:(WKWebView *)webView didCommitNavigation:(null_unspecified WKNavigation *)navigation 
    //NSLog(@"网页开始接收网页内容");

- (void)webView:(WKWebView *)webView didFinishNavigation:(null_unspecified WKNavigation *)navigation 
    //NSLog(@"网页导航加载完毕");
    //[SVProgressHUD dismiss];
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
    
    self.title = webView.title;
    [webView evaluateJavaScript:@"document.title" completionHandler:^(id _Nullable ss, NSError * _Nullable error) 
        //NSLog(@"----document.title:%@---webView title:%@",ss,webView.title);
    ];
    //self.progress.alpha  = 0;
    


- (void)webView:(WKWebView *)webView didFailNavigation:(null_unspecified WKNavigation *)navigation withError:(NSError *)error 
    //NSLog(@"加载失败,失败原因:%@",[error description]);
    //self.progress.alpha = 0;

- (void)webViewWebContentProcessDidTerminate:(WKWebView *)webView 
    //NSLog(@"网页加载内容进程终止");



#pragma mark - KVO监听
// 第三部：完成监听方法
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context 
    
    if ([object isEqual:_webView] && [keyPath isEqualToString:@"estimatedProgress"])  // 进度条
        
        CGFloat newprogress = [[change objectForKey:NSKeyValueChangeNewKey] doubleValue];
        //NSLog(@"打印测试进度值：%f", newprogress);
        
        if (newprogress == 1)  // 加载完成
            // 首先加载到头
            [self.progressView setProgress:newprogress animated:YES];
            // 之后0.3秒延迟隐藏
            __weak typeof(self) weakSelf = self;
            dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 0.3 * NSEC_PER_SEC), dispatch_get_main_queue(), ^
                
                weakSelf.progressView.hidden = YES;
                [weakSelf.progressView setProgress:0 animated:NO];
            );
            
         else  // 加载中
            self.progressView.hidden = NO;
            [self.progressView setProgress:newprogress animated:YES];
        
     else if ([object isEqual:_webView] && [keyPath isEqualToString:@"title"])  // 标题
        
        //self.title = _webView.title;
     else  // 其他
        
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    


-(void)dealloc
    NSLog(@"webVC dealloc = %@",self);
    [_webView removeObserver:self forKeyPath:@"estimatedProgress"];
    [_webView removeObserver:self forKeyPath:@"title"];


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


/*
 #pragma mark - Navigation
 
 // In a storyboard-based application, you will often want to do a little preparation before navigation
 - (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender 
 // Get the new view controller using [segue destinationViewController].
 // Pass the selected object to the new view controller.
 
 */

@end