//添加观察者模式
    [self.webView addObserver:self forKeyPath:@"estimatedProgress" options:NSKeyValueObservingOptionNew context:nil];

#pragma mark - 监听加载进度
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    
    if ([keyPath isEqualToString:@"estimatedProgress"]) {
        
        if (object ==self.webView) {
            [_progressView setAlpha:1.0f];
            [_progressView setProgress:self.webView.estimatedProgress animated:YES];
            
            if(self.webView.estimatedProgress >=1.0f) {
                
                [UIView animateWithDuration:0.3 delay:0.3 options:UIViewAnimationOptionCurveEaseOut animations:^{
                    [_progressView setAlpha:0.0f];
                } completion:^(BOOL finished) {
                    [_progressView setProgress:0.0f animated:NO];
                }];
                
            }
        }
        else
        {
            [super observeValueForKeyPath:keyPath ofObject:object  change:change context:context];
        }
        
    }
}

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