【WKWebview填坑(一)】WKWebview 添加User-Agent ios12下的兼容问题

网上好多WKWebview的方法都差不多而且基本都是错的，下面是我自己整理的添加User-Agent的方法，兼容ios8，还有最新的ios12，具体代码如下：

if (@available(iOS 12.0, *)) 
     NSString *baseAgent = [self.myWebView valueForKey:@"applicationNameForUserAgent"];
    NSString *userAgent = [NSString stringWithFormat:@"%@ YCL",baseAgent];
    [self.myWebView setValue:userAgent forKey:@"applicationNameForUserAgent"];
}

JRWeakSelf(weakSelf);
[self.myWebView evaluateJavaScript:@"navigator.userAgent" completionHandler:^(id result, NSError *error) {
    
    NSString *oldAgent = result;
    if ([oldAgent rangeOfString:@"YCL"].location != NSNotFound) {
        return ;
    }
    NSString *newAgent = [NSString stringWithFormat:@"%@ %@", oldAgent, @"YCL"];
    NSDictionary *dictionary = [NSDictionary dictionaryWithObjectsAndKeys:newAgent, @"UserAgent", nil];
    [[NSUserDefaults standardUserDefaults] registerDefaults:dictionary];
    [[NSUserDefaults standardUserDefaults] synchronize];
    if (@available(iOS 9.0, *)) {
        [weakSelf.myWebView setCustomUserAgent:newAgent];
    } else {
        [weakSelf.myWebView setValue:newAgent forKey:@"applicationNameForUserAgent"];
    }
}];

代码不用写很多，ios12需要先初始化一个userAgent,因为mebview获取userAgent是异步的，ios12的load时机和添加userAgent的顺序不一样，具体原因等研究下ios12代码再说...