WKWebView添加了estimatedProgress屬性（double型別），我們可以利用該屬性來設定UIProgressView

• 為頁面新增UIProgressView屬性

@property (nonatomic, strong) WKWebView *mywebView;
@property (nonatomic, strong) UIProgressView *progressView;//設定載入進度條

• 懶載入UIProgressView

-(UIProgressView *)progressView{
    if (!_progressView) {
        _progressView                   = [[UIProgressView alloc]
                                           initWithProgressViewStyle:UIProgressViewStyleDefault];
        _progressView.frame             = CGRectMake(0, 64, screen_width, 5);

        [_progressView setTrackTintColor:[UIColor colorWithRed:240.0/255
                                                         green:240.0/255
                                                          blue:240.0/255
                                                         alpha:1.0]]
 
;
        _progressView.progressTintColor = [UIColor greenColor];


    }
    return _progressView;
}

• 在初始化WKWebView時（我是在懶載入時） kvo 新增監控

 [_mywebView addObserver:self
                     forKeyPath:NSStringFromSelector(@selector(estimatedProgress))
                        options:0
                        context:
 
nil];

• 頁面開始載入時，隱藏進度條

//開始載入
-(void)webView:(WKWebView *)webView
  didStartProvisionalNavigation:(WKNavigation *)navigation{
    //開始載入的時候，讓進度條顯示
    self.progressView.hidden = NO;
}

• kvo 監聽進度

//kvo 監聽進度
-(void)observeValueForKeyPath:(NSString *)keyPath
                     ofObject:(id)object
                       change:(NSDictionary
 
<NSKeyValueChangeKey,id> *)change
                      context:(void *)context{

    if ([keyPath isEqualToString:NSStringFromSelector(@selector(estimatedProgress))]
        && object == self.mywebView) {
        [self.progressView setAlpha:1.0f];
        BOOL animated = self.mywebView.estimatedProgress > self.progressView.progress;
        [self.progressView setProgress:self.mywebView.estimatedProgress
                              animated:animated];

        if (self.mywebView.estimatedProgress >= 1.0f) {
            [UIView animateWithDuration:0.3f
                                  delay:0.3f
                                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];
    }
}

• 在dealloc方法裡移除監聽

-(void)dealloc{
    [self.mywebView removeObserver:self
                        forKeyPath:NSStringFromSelector(@selector(estimatedProgress))];
}