无法使用facebook sdk访问IOS的电子邮件字段

Question

我正在使用Graph API，但我无法弄清楚如何获取登录用户的电子邮件地址。

[FBSession openActiveSessionWithReadPermissions:@[@"public_profile", @"email"] allowLoginUI:NO
            completionHandler:^(FBSession *session, FBSessionState state, NSError *error) {
    // Handler for session state changes
    // This method will be called EACH time the session state changes,
    // also for intermediate states and NOT just when the session open
    [self sessionStateChanged:session state:state error:error];
}];