iOS - 添加User Agent

1、全局设置webview，不论是UIWebView还是WKWebView

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
NSDictionary *infoDictionary = [[NSBundle mainBundle] infoDictionary];
    NSString *app_Version = [infoDictionary objectForKey:@"CFBundleShortVersionString"];
    NSString *ua = [NSString stringWithFormat:@"/xxxxflag/%@",app_Version];
    
    UIWebView *webView = [[UIWebView alloc] init];
  //直接获取userAgent
    NSString *userAgent = [webView stringByEvaluatingJavaScriptFromString:@"navigator.userAgent"];
    NSString *newUserAgent = [userAgent stringByAppendingString:ua];
    NSDictionary *dictionary = [NSDictionary dictionaryWithObjectsAndKeys:newUserAgent, @"UserAgent", nil];
    [[NSUserDefaults standardUserDefaults] registerDefaults:dictionary];
}

2、全局设置webview，不论是UIWebView还是WKWebView

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    self.webView = [[WKWebView alloc] init];
    NSDictionary *infoDictionary = [[NSBundle mainBundle] infoDictionary];
    NSString *app_Version = [infoDictionary objectForKey:@"CFBundleShortVersionString"];
    NSString *ua = [NSString stringWithFormat:@"/xxxxflag/%@",app_Version];
    
    if (@available(iOS 12.0, *)){
        //由于iOS12的UA改为异步，所以不管在js还是客户端第一次加载都获取不到，所以此时需要先设置好再去获取
        NSString *userAgent = [_webView valueForKey:@"applicationNameForUserAgent"];
        NSString *newUserAgent = [NSString stringWithFormat:@"%@%@",userAgent,ua];
        [_webView setValue:newUserAgent forKey:@"applicationNameForUserAgent"];
        //        NSLog(@"%@>>>%@>>>>>",userAgent,newUserAgent);
    }
//在回调里获取userAgent即result
    [_webView evaluateJavaScript:@"navigator.userAgent" completionHandler:^(id _Nullable result, NSError * _Nullable error) {
        NSString *userAgent = result;
        
        if ([userAgent rangeOfString:ua].location != NSNotFound) {
            return ;
        }
        NSString *newUserAgent = [userAgent stringByAppendingString:ua];
        //        NSLog(@"%@>>>%@>>>>>",userAgent,newUserAgent);
        NSDictionary *dictionary = [NSDictionary dictionaryWithObjectsAndKeys:newUserAgent,@"UserAgent", nil];
        [[NSUserDefaults standardUserDefaults] registerDefaults:dictionary];
        [[NSUserDefaults standardUserDefaults] synchronize];
        //不添加以下代码则只是在本地更改UA，网页并未同步更改
        if (@available(iOS 9.0, *)) {
            [_webView setCustomUserAgent:newUserAgent];
        } else {
            [_webView setValue:newUserAgent forKey:@"applicationNameForUserAgent"];
        }
    }]; //加载请求必须同步在设置UA的后面
}

注意：WKWebView不能使用局部声明，需要放在类扩展中，否则无效

3、页面内设置WKWebView,创建WKWebView之后调用以下方法

- (void)setWebViewUA {
    
    NSDictionary *infoDictionary = [[NSBundle mainBundle] infoDictionary];
    NSString *app_Version = [infoDictionary objectForKey:@"CFBundleShortVersionString"];
    NSString *ua = [NSString stringWithFormat:@"/xxxxflag/%@",app_Version];
    
    if (@available(iOS 12.0, *)){
        //由于iOS12的UA改为异步，所以不管在js还是客户端第一次加载都获取不到，所以此时需要先设置好再去获取
        NSString *userAgent = [_webView valueForKey:@"applicationNameForUserAgent"];
        NSString *newUserAgent = [NSString stringWithFormat:@"%@%@",userAgent,ua];
        [_webView setValue:newUserAgent forKey:@"applicationNameForUserAgent"];
        //        NSLog(@"%@>>>%@>>>>>",userAgent,newUserAgent);
    }
    [_webView evaluateJavaScript:@"navigator.userAgent" completionHandler:^(id _Nullable result, NSError * _Nullable error) {
        NSString *userAgent = result;
        
        if ([userAgent rangeOfString:ua].location != NSNotFound) {
            return ;
        }
        NSString *newUserAgent = [userAgent stringByAppendingString:ua];
        //        NSLog(@"%@>>>%@>>>>>",userAgent,newUserAgent);
        NSDictionary *dictionary = [NSDictionary dictionaryWithObjectsAndKeys:newUserAgent,@"UserAgent", nil];
        [[NSUserDefaults standardUserDefaults] registerDefaults:dictionary];
        [[NSUserDefaults standardUserDefaults] synchronize];
        //不添加以下代码则只是在本地更改UA，网页并未同步更改
        if (@available(iOS 9.0, *)) {
            [_webView setCustomUserAgent:newUserAgent];
        } else {
            [_webView setValue:newUserAgent forKey:@"applicationNameForUserAgent"];
        }
    }]; //加载请求必须同步在设置UA的后面
}

4、页面内设置UIWebView,创建UIWebView之后调用以下方法

    UIWebView *webView = [[UIWebView alloc] init];
    NSString *userAgent = [webView stringByEvaluatingJavaScriptFromString:@"navigator.userAgent"];
    NSString *newUserAgent = [userAgent stringByAppendingString:@" Appended Custom User Agent"];
    NSDictionary *dictionary = [NSDictionary dictionaryWithObjectsAndKeys:newUserAgent, @"UserAgent", nil];
    [[NSUserDefaults standardUserDefaults] registerDefaults:dictionary];

注意：UserAgent的设置都是要在webview初始化后，才能生效。
ViewController里面进行的局部设置，在页面dealloc后，UserAgent随之失效。

5、在项目的网络请求中，我们也可以进行httpHeader设置UserAgent

// AFN中 在 AFHTTPRequestSerializer 类中
//调用- (void)setValue:(nullable NSString *)value forHTTPHeaderField：(NSString*)field; 给请求头设置参数 @"User-A