ios - WKWebView でのローカル ファイルの読み込みがデバイスで機能しない

Question

wkwebview で (ドキュメント ディレクトリから) ローカルの epub ファイルを読み込めません。シミュレーターでは機能しますが、デバイスでは機能しません。ここからiOS 8のバグだと知り ました。iOS 8 では既に解決されていますか? どうすればいいのか教えてください。デバイスでエラーが発生しました-

The operation couldn't be completed. (KCFErrorDomainCFNetwork error 1.)

ここにコードスニペットがあります -

-(void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];

    [self.webView removeObserver:self forKeyPath:@"loading"];
    [self.webView removeObserver:self forKeyPath:@"estimatedProgress"];
}


-(void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];

    [self.webView addObserver:self forKeyPath:@"loading" options:NSKeyValueObservingOptionNew context:nil];
    [self.webView addObserver:self forKeyPath:@"estimatedProgress" options:NSKeyValueObservingOptionNew context:nil];
    [self.progressView setProgress:0.0f animated:NO];

    if ([self.documentDirectory checkEpubFileIfExistsAtPath:self.epubFolder]) {

        NSString *filePath = [NSString stringWithFormat:@"%@/%@/%@/OEBPS/%@", [self.documentDirectory getDocumentsDirectory], self.epubFolder, self.epubName, [_html_link substringToIndex:[_html_link rangeOfString:@"#"].location]];

        //Loading webview with progress bar action
        if ([_html_link rangeOfString:@"#"].location != NSNotFound) {

            self.tag = [_html_link substringFromIndex:[_html_link rangeOfString:@"#"].location];
            NSURL *URL = [NSURL fileURLWithPath:filePath];
            NSURLRequest *request = [NSURLRequest requestWithURL:URL];
            [self.webView loadRequest:request];
        }

    } else {

        NSDictionary *object = [self.alertMessages getMessageObj:@"translationNotAvailable"];
        [self presentViewController:[self.alertController alertWithCustomOkayAction:[object objectForKey:@"title"] message:[object objectForKey:@"msg"] callback:^(void) {

            [self dismissViewControllerAnimated:YES completion:nil];

        }] animated:YES completion:nil];
    }
}

//Constraints for Web View
- (void) setConstraintsForWebView {
    [self.webView setTranslatesAutoresizingMaskIntoConstraints:NO];

    WKWebView *webView = self.webView;
    UIProgressView *progressView = self.progressView;
    UIToolbar *toolBar = self.toolBar;

    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-8-[webView]-8-|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(webView)]];

    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[progressView]-0-[webView]-[toolBar]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(progressView, webView, toolBar)]];
}

- (void)viewDidLoad {
    [super viewDidLoad];

    //Do any additional setup after loading the view.
    self.alertController = [AlertController new];
    self.alertMessages = [AlertMessages new];
    self.documentDirectory = [DocumentDirectory new];
    self.languageController = [LanguageController new];

    //Set observer for webview load
    self.webView = [[WKWebView alloc] initWithFrame:CGRectZero];
    self.webView.navigationDelegate = self;
    [self.view insertSubview:self.webView belowSubview:self.progressView];
    [self setConstraintsForWebView];

}

#pragma mark KVO

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    if ([keyPath isEqualToString:@"loading"]) {
        [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:self.webView.loading];
    } else if ([keyPath isEqualToString:@"estimatedProgress"]) {
        self.progressView.hidden = self.webView.estimatedProgress == 1;
        self.progressView.progress = self.webView.estimatedProgress;
    }
}


#pragma mark Web view navigation delegate

- (void)webView:(WKWebView *)webView didFinishNavigation:(WKNavigation *)navigation {
    [self.progressView setProgress:0.0f animated:NO];
    if (self.tag) {
        [self.webView evaluateJavaScript:[NSString stringWithFormat:@"window.location.hash='%@'", self.tag] completionHandler:nil];
    }
}

- (void)webView:(WKWebView *)webView didFailProvisionalNavigation:(WKNavigation *)navigation withError:(NSError *)error {

    [self presentViewController:[self.alertController alertWithAction:@"Error!" message:error.localizedDescription] animated:YES completion:nil];
}