How to use different User-Agent in different iOS Webview request - ios

Question

I know I can use the below code to change the default agent:
NSDictionary *dictionary = [NSDictionary dictionaryWithObjectsAndKeys:#"Your user agent", #"UserAgent", nil];
[[NSUserDefaults standardUserDefaults] registerDefaults:dictionary];
but I want to request a different User-Agent for different requests. Examples: request 'www.google.com', use agent=‘google Agent’, request 'www.github.com', use agent='github Agent'.
I have tried the below way to set the 'User_Agent' in each request, but it doesn't seem to work.
- (void)viewDidLoad {
NSString *urlAddress = #"http://www.amazon.com";
//Create a URL object.
NSURL *url = [NSURL URLWithString:urlAddress];
//URL Requst Object
NSMutableURLRequest *requestObj = [NSMutableURLRequest requestWithURL:url];
[requestObj setValue:#"Foobar/1.0" forHTTPHeaderField:#"User_Agent"];
// But the value is not "Foobar/1.0"
NSString* secretAgent = [webView stringByEvaluatingJavaScriptFromString:#"navigator.userAgent"];
NSLog(#"agent - %#", secretAgent);
//Load the request in the UIWebView.
[webView loadRequest:requestObj];
}
One more question:
It seems a change to the default agent only work change in 'AppDelegate' or 'initialize'. Am I right? Because I try to change in 'viewDidLoad' but it doesn't seem to work.

Answer 1

I observed that if you load any url in webView with a user-agent set
to it. After some time you load the different url & different user
agent but used the same allocated WebView instane.The web view will
load the new url but can not set new user-agent. It just set old one
that you have set before loading first time.
You can not change untill you initiate new instanse of UIWebview(or
we can say that user agent can be set once per session). So I coame to result that user-agent can be set only once.
What I did for this problem is, I allocated new instance when I want set new user-agent.

Answer 2

You don't need to set it using JavaScript.
You have misspelled User-Agent. Use this minimal code taken from here
NSString* userAgent = #"My Cool User Agent";
NSURL* url = [NSURL URLWithString:#"http://whatsmyuseragent.com/"];
NSMutableURLRequest* request = [[NSMutableURLRequest alloc] initWithURL:url];
[request setValue:userAgent forHTTPHeaderField:#"User-Agent"];