前言：

有個項目需求，要區分打開H5是在本地APP還是在手機瀏覽器，前端伙伴說需要配合修改默認的 UserAgent,以便區分。

一、如何獲取UserAgent

UIWebView方式：

UIWebView *webView = [[UIWebView alloc] initWithFrame:CGRectZero];
NSString *userAgent = [webView stringByEvaluatingJavaScriptFromString:@"navigator.userAgent"];
DLog(@"userAgent :%@", userAgent);

WKWebView方式：

// 注意這個方法是異步的
WKWebView *wkWebView = [[WKWebView alloc] initWithFrame:CGRectZero];
[wkWebView evaluateJavaScript:@"navigator.userAgent" completionHandler:^(id result, NSError *error) {
    DLog(@"userAgent :%@", result);
 }];

默認UserAgent輸出：

Mozilla/5.0 (iPhone; CPU iPhone OS 8_4 like Mac OS X) AppleWebKit/600.1.4 (KHTML, like Gecko) Mobile/12H143

微信 iOS版的 ：UserAgent

mozilla/5.0 (iphone; cpu iphone os 5_1_1 like mac os x) applewebkit/534.46 (khtml, like gecko) mobile/9b206 micromessenger/5.0
其中micromessenger就是自定義的

二、如何修改UserAgent

方案一，修改全局UserAgent值（這里是在原有基礎上拼接自定義的字符串）

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    UIWebView *webView = [[UIWebView alloc] initWithFrame:CGRectZero];
    NSString *userAgent = [webView stringByEvaluatingJavaScriptFromString:@"navigator.userAgent"];
    NSString *newUserAgent = [userAgent stringByAppendingString:@" native_iOS"];//自定義需要拼接的字符串
    NSDictionary *dictionary = [NSDictionary dictionaryWithObjectsAndKeys:newUserAgent, @"UserAgent", nil];
    [[NSUserDefaults standardUserDefaults] registerDefaults:dictionary];
}

方案二，自定義UserAgent值

WKWebView *wkWebView = [[WKWebView alloc] initWithFrame:self.view.bounds];
[self.view addSubview: wkWebView];
NSString *customUserAgent = @"native_iOS";
[[NSUserDefaults standardUserDefaults] registerDefaults:@{@"UserAgent":customUserAgent}];
NSURL *url = [NSURL URLWithString:self.strUrl];
NSURLRequest *request = [NSURLRequest requestWithURL:url
                                             cachePolicy:NSURLRequestUseProtocolCachePolicy
                                         timeoutInterval:10.f];
[self.wkWebView loadRequest:request];

方案三

 self.wkWebView = [[WKWebView alloc] initWithFrame:self.view.bounds];
 __weak typeof(self) weakSelf = self;
 [self.wkWebView evaluateJavaScript:@"navigator.userAgent" completionHandler:^(id result, NSError *error) {
        __strong typeof(weakSelf) strongSelf = weakSelf;
        NSString *userAgent = result;
        NSString *newUserAgent = [userAgent stringByAppendingString:@" native_iOS"];
        NSDictionary *dictionary = [NSDictionary dictionaryWithObjectsAndKeys:newUserAgent, @"UserAgent", nil];
        [[NSUserDefaults standardUserDefaults] registerDefaults:dictionary];
        // needs retain because `evaluateJavaScript:` is asynchronous
        strongSelf.wkWebView = [[WKWebView alloc] initWithFrame:strongSelf.view.bounds];
  }];
  [self.wkWebView loadRequest:request];

三、問題& 思考

在測試的時候，發現方案二、三第一次運行的時候，還是顯示默認的值，第二次才會顯示自定義的值，其中原因還不明，如有朋友解決麻煩告訴一下，謝謝。