/**

*  得到原始的useragent

*/

NSString *oldAgent = [self.webView stringByEvaluatingJavaScriptFromString:@"navigator.userAgent"];

/**

*  在后面添加你要追加的字符串

*/

NSString *newAgent = [oldAgent stringByAppendingString:@"你要追加的字符串"];

/**

注册新的usergent

*/

NSDictionary *dictionnary = [[NSDictionary alloc] initWithObjectsAndKeys:newAgent, @"UserAgent", nil];

[[NSUserDefaults standardUserDefaults] registerDefaults:dictionnary];