iOS中WKWebView仿微信加载进度条

@property (nonatomic, strong) WKWebView *mywebView;
@property (nonatomic, strong) UIProgressView *progressView;//设置加载进度条

-(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;
}

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

//开始加载
-(void)webView:(WKWebView *)webView
 didStartProvisionalNavigation:(WKNavigation *)navigation{
 //开始加载的时候，让进度条显示
 self.progressView.hidden = NO;
}

//kvo 监听进度
-(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];
 }
}

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