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