1、添加UIProgressView属性

@property (nonatomic, strong) WKWebView *wkWebView;
@property (nonatomic, strong) UIProgressView *progressView;

2、初始化progressView

- (void)viewDidLoad {
    [super viewDidLoad];    
    //进度条初始化
    self.progressView = [[UIProgressView alloc] initWithFrame:CGRectMake(0, 20, [[UIScreen mainScreen] bounds].size.width, 2)];
    self.progressView.backgroundColor = [UIColor blueColor];
    //设置进度条的高度，下面这句代码表示进度条的宽度变为原来的1倍，高度变为原来的1.5倍.
    self.progressView.transform = CGAffineTransformMakeScale(1.0f, 1.5f);
    [self.view addSubview:self.progressView];
}

3、添加KVO，WKWebView有一个属性estimatedProgress，就是当前网页加载的进度，所以监听这个属性。

[self.wkWebView addObserver:self forKeyPath:@"estimatedProgress" options:NSKeyValueObservingOptionNew context:nil];

4、在监听方法中获取网页加载的进度，并将进度赋给progressView.progress

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context {
    if ([keyPath isEqualToString:@"estimatedProgress"]) {
        self.progressView.progress = self.wkWebView.estimatedProgress;
        if (self.progressView.progress == 1) {
            /*
             *添加一个简单的动画，将progressView的Height变为1.4倍，在开始加载网页的代理中会恢复为1.5倍
             *动画时长0.25s，延时0.3s后开始动画
             *动画结束后将progressView隐藏
             */
            __weak typeof (self)weakSelf = self;
            [UIView animateWithDuration:0.25f delay:0.3f options:UIViewAnimationOptionCurveEaseOut animations:^{
                weakSelf.progressView.transform = CGAffineTransformMakeScale(1.0f, 1.4f);
            } completion:^(BOOL finished) {
                weakSelf.progressView.hidden = YES;
 
            }];
        }    
    }else{
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
}

5、在WKWebViewd的代理中展示进度条，加载完成后隐藏进度条

//开始加载
- (void)webView:(WKWebView *)webView didStartProvisionalNavigation:(WKNavigation *)navigation {
    NSLog(@"开始加载网页");
    //开始加载网页时展示出progressView
    self.progressView.hidden = NO;
    //开始加载网页的时候将progressView的Height恢复为1.5倍
    self.progressView.transform = CGAffineTransformMakeScale(1.0f, 1.5f);
    //防止progressView被网页挡住
    [self.view bringSubviewToFront:self.progressView];
}
 
//加载完成
- (void)webView:(WKWebView *)webView didFinishNavigation:(WKNavigation *)navigation {
    NSLog(@"加载完成");
    //加载完成后隐藏progressView
    //self.progressView.hidden = YES;
}
 
//加载失败
- (void)webView:(WKWebView *)webView didFailProvisionalNavigation:(WKNavigation *)navigation withError:(NSError *)error {
    NSLog(@"加载失败");
    //加载失败同样需要隐藏progressView
    //self.progressView.hidden = YES;
}

6、在dealloc中取消监听

- (void)dealloc {
    [self.wkWebView removeObserver:self forKeyPath:@"estimatedProgress"];
}