当使用loadRequest来读取本地的HTML时，WKWebView是无法读取成功的，后台会出现如下的提示：
Could not create a sandbox extension for /
原因是WKWebView是不允许通过loadRequest的方法来加载本地根目录的HTML文件。
而在iOS9的SDK中加入了以下方法来加载本地的HTML文件：
[WKWebView loadFileURL:allowingReadAccessToURL:]
但是在iOS9以下的版本是没提供这个便利的方法的。以下为解决方案的思路，就是在iOS9以下版本时，先将本地HTML文件的数据copy到tmp目录中，然后再使用loadRequest来加载。但是如果在HTML中加入了其他资源文件，例如js，css，image等必须一同copy到temp中。这个是最蛋疼的事情了。

解决方法如下

1.Objective-C：

//将文件copy到tmp目录
- (NSURL *)fileURLForBuggyWKWebView8:(NSURL *)fileURL {
    NSError *error = nil;
    if (!fileURL.fileURL || ![fileURL checkResourceIsReachableAndReturnError:&error]) {
        return nil;
    }
    // Create "/temp/www" directory
    NSFileManager *fileManager= [NSFileManager defaultManager];
    NSURL *temDirURL = [[NSURL fileURLWithPath:NSTemporaryDirectory()] URLByAppendingPathComponent:@"www"];
    [fileManager createDirectoryAtURL:temDirURL withIntermediateDirectories:YES attributes:nil error:&error];

    NSURL *dstURL = [temDirURL URLByAppendingPathComponent:fileURL.lastPathComponent];
    // Now copy given file to the temp directory
    [fileManager removeItemAtURL:dstURL error:&error];
    [fileManager copyItemAtURL:fileURL toURL:dstURL error:&error];
    // Files in "/temp/www" load flawlesly :)
    return dstURL;
}

//调用逻辑
 NSString *path = [[NSBundle mainBundle] pathForResource:@"indexoff" ofType:@"html"];
    if(path){
        if ([[UIDevice currentDevice].systemVersion floatValue] >= 9.0) {
            // iOS9. One year later things are OK.
            NSURL *fileURL = [NSURL fileURLWithPath:path];
            [self.webView loadFileURL:fileURL allowingReadAccessToURL:fileURL];
        } else {
            // iOS8. Things can be workaround-ed
            //   Brave people can do just this
            //   fileURL = try! pathForBuggyWKWebView8(fileURL)
            //   webView.loadRequest(NSURLRequest(URL: fileURL))

            NSURL *fileURL = [self.fileHelper fileURLForBuggyWKWebView8:[NSURL fileURLWithPath:path]];
            NSURLRequest *request = [NSURLRequest requestWithURL:fileURL];
            [self.webView loadRequest:request];
        }
    }

2.Swift

//将文件copy到tmp目录
func fileURLForBuggyWKWebView8(fileURL: NSURL) throws -> NSURL {
    // Some safety checks
    var error:NSError? = nil;
    if (!fileURL.fileURL || !fileURL.checkResourceIsReachableAndReturnError(&error)) {
        throw error ?? NSError(
            domain: "BuggyWKWebViewDomain",
            code: 1001,
            userInfo: [NSLocalizedDescriptionKey: NSLocalizedString("URL must be a file URL.", comment:"")])
    }

    // Create "/temp/www" directory
    let fm = NSFileManager.defaultManager()
    let tmpDirURL = NSURL.fileURLWithPath(NSTemporaryDirectory()).URLByAppendingPathComponent("www")
    try! fm.createDirectoryAtURL(tmpDirURL, withIntermediateDirectories: true, attributes: nil)

    // Now copy given file to the temp directory
    let dstURL = tmpDirURL.URLByAppendingPathComponent(fileURL.lastPathComponent!)
    let _ = try? fileMgr.removeItemAtURL(dstURL)
    try! fm.copyItemAtURL(fileURL, toURL: dstURL)

    // Files in "/temp/www" load flawlesly :)
    return dstURL
}

//方法调用

    var filePath = NSBundle.mainBundle().pathForResource("file", ofType: "pdf")

    if #available(iOS 9.0, *) {
        // iOS9. One year later things are OK.
        webView.loadFileURL(fileURL, allowingReadAccessToURL: fileURL)
    } else {
        // iOS8. Things can be workaround-ed
        //   Brave people can do just this
        //   fileURL = try! pathForBuggyWKWebView8(fileURL)
        //   webView.loadRequest(NSURLRequest(URL: fileURL))
        do {
            fileURL = try fileURLForBuggyWKWebView8(fileURL)
            webView.loadRequest(NSURLRequest(URL: fileURL))
        } catch let error as NSError {
            print("Error: " + error.debugDescription)
        }
    }

2. WKWebView - WKNavigationDelegate使用

特别提醒一点，在使用以下delegate的方法时

- (void)webView:(WKWebView *)webView decidePolicyForNavigationAction:(WKNavigationAction *)navigationAction decisionHandler:(void (^)(WKNavigationActionPolicy))decisionHandler

需执行decisionHandler的block。

例如：

- (void)webView:(WKWebView *)webView decidePolicyForNavigationAction:(WKNavigationAction *)navigationAction decisionHandler:(void (^)(WKNavigationActionPolicy))decisionHandler {

    NSURLRequest *request = navigationAction.request;
    WMPageActionType actionType = ActionTypeNone;
    WKNavigationActionPolicy actionPolicy = WKNavigationActionPolicyAllow;
    if([request.URL.absoluteString hasPrefix:OC_CLOSE_REQUEST]){
        actionType = ActionTypeClose;
        actionPolicy = WKNavigationActionPolicyCancel;
    }
    if(self.actionDelegate && [self.actionDelegate respondsToSelector:@selector(webView:action:type:)]) {
        [self.actionDelegate webView:webView action:navigationAction type:actionType];
    }
   //这句是必须加上的，不然会异常
    decisionHandler(actionPolicy);
}

3.WKWebView-JS执行方法

WKWebView JS执行方法与UIWebView不一样了。

- (void)evaluateJavaScript:(NSString *)javaScriptString completionHandler:(void (^)(id, NSError *))completionHandler;

completionHandler 拥有两个参数，一个是返回错误，一个可以返回执行脚本后的返回值