ios 如何实现UIWebView的缓存

NSURLRequestCachePolicy policy;
    if ([MANAGER_UTIL isEnableNetWork]) {
        policy = NSURLRequestReloadIgnoringLocalAndRemoteCacheData;
    }else {
        policy = NSURLRequestReturnCacheDataDontLoad;
    }

    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:self.url] cachePolicy:policy timeoutInterval:60];
    [webView loadRequest:request];