iOS 修改UIWebView的UserAgent

//get the original user-agent of webview
    UIWebView *webView = [[UIWebView alloc] initWithFrame:CGRectZero];
    NSString *oldAgent = [webView stringByEvaluatingJavaScriptFromString:@"navigator.userAgent"];
    NSLog(@"old agent :%@", oldAgent);
    
    //add my info to the new agent
    NSString *newAgent = [oldAgent stringByAppendingString:@" Jiecao/2.4.7 ch_appstore"];
    NSLog(@"new agent :%@", newAgent);
    
    //regist the new agent
    NSDictionary *dictionnary = [[NSDictionary alloc] initWithObjectsAndKeys:newAgent, @"UserAgent", nil];
    [[NSUserDefaults standardUserDefaults] registerDefaults:dictionnary];