实际项目中可能会用到进度条来显示一个网页的加载进度，不知道的人还以为有什么很神奇的地方，其实很简单，主要是通过监听webView的一个属性estimatedProgress。直接上代码吧，代码量很少的。

@property (weak, nonatomic) WKWebView *webView;
@property (weak, nonatomic) CALayer *progresslayer;

界面布局。

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor whiteColor];
    self.automaticallyAdjustsScrollViewInsets = NO;
    WKWebView *webView = [[WKWebView alloc]initWithFrame:CGRectMake(0, 63, self.view.frame.size.width, self.view.frame.size.height - 64)];
    [self.view addSubview:webView];
    self.webView = webView;
    //添加属性监听
    [webView addObserver:self forKeyPath:@"estimatedProgress" options:NSKeyValueObservingOptionNew context:nil];
    
    //进度条
    UIView *progress = [[UIView alloc]initWithFrame:CGRectMake(0, 64, CGRectGetWidth(self.view.frame), 3)];
    progress.backgroundColor = [UIColor clearColor];
    [self.view addSubview:progress];

    CALayer *layer = [CALayer layer];
    layer.frame = CGRectMake(0, 0, 0, 3);
    layer.backgroundColor = [UIColor blueColor].CGColor;
    [progress.layer addSublayer:layer];
    self.progresslayer = layer;
    
    [webView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"https://bing.com"]]];
}

监听进度，更新界面。

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context{
    if ([keyPath isEqualToString:@"estimatedProgress"]) {
        //NSLog(@"%@", change);
        self.progresslayer.opacity = 1;
        self.progresslayer.frame = CGRectMake(0, 0, self.view.bounds.size.width * [change[NSKeyValueChangeNewKey] floatValue], 3);
        if ([change[NSKeyValueChangeNewKey] floatValue] == 1) {
            dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(.2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
                self.progresslayer.opacity = 0;
            });
            dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(.8 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
                self.progresslayer.frame = CGRectMake(0, 0, 0, 3);
            });
        }
    }else{
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
}

温馨提示，不要忘记dealloc了。

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

so easy！！！！！！！！！