最近写项目的时候，有一个需求，要加载HTML页面，并且显示HTML页面的title，查找了相关文章，找到了一份非常合适的文章，想看原文请点击这里。

WKWebView 的estimatedProgress和title 都是KVO模式，所以可以添加监听：

[webView addObserver:self forKeyPath:@"estimatedProgress" options:NSKeyValueObservingOptionNew context:NULL];
[webView addObserver:self forKeyPath:@"title" options:NSKeyValueObservingOptionNew context:NULL];

监听的实现方法：

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {

    if ([keyPath isEqualToString:@"estimatedProgress"]) {

        if (object == webView) {
            [self.progressView setAlpha:1.0f];
            [self.progressView setProgress:self.currentSubView.webView.estimatedProgress animated:YES];

            if(self.currentSubView.webView.estimatedProgress >= 1.0f) {

                [UIView animateWithDuration:0.3 delay:0.3 options:UIViewAnimationOptionCurveEaseOut animations:^{
                    [self.progressView setAlpha:0.0f];
                } completion:^(BOOL finished) {
                    [self.progressView setProgress:0.0f animated:NO];
                }];

            }
        }
        else
        {
            [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
        }

    }
    else if ([keyPath isEqualToString:@"title"])
    {
        if (object == self.webView) {
            self.title = self.webView.title;

        }
        else
        {
            [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];

        }
    }
    else {

        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
}

进度条增加了动画，类似safari的进度效果

注意销毁时一定要移除监听

[webView removeObserver:self forKeyPath:@"estimatedProgress"];
[webView removeObserver:self forKeyPath:@"title"];