如何检查 Facebook 账号是否存在？

Question

我正在尝试实现Facebook发布程序。你能帮我了解如何检查iPhone(iOS6 特性)中是否存在该账户吗？我看过WWDC会议，他们使用了以下代码：

if (self.accountStore == nil) {
    self.accountStore = [[ACAccountStore alloc] init];
}   
ACAccountType * facebookAccountType = [self.accountStore accountTypeWithAccountTypeIdentifier:ACAccountTypeIdentifierFacebook];
//Now we can obtain some extra permissions
NSArray * permissions = @[@"publish_stream"];
//NSArray * permissions = @[@"user_about_me"];
NSDictionary * dict = @{ACFacebookAppIdKey : FB_APP_ID, ACFacebookPermissionsKey : permissions, ACFacebookAudienceKey : ACFacebookAudienceEveryone};
[self.accountStore requestAccessToAccountsWithType:facebookAccountType options:dict completion:^(BOOL granted, NSError *error) {
    __block NSString * statusText = nil;
    if (granted) {
        statusText = @"Logged in";
        NSArray * accounts = [self.accountStore accountsWithAccountType:facebookAccountType];
        self.facebookAccount = [accounts lastObject];
        NSLog(@"account is: %@", self.facebookAccount);
        self.statusLabel.text = statusText;
        [self postToFeed];
    }
    else {
        self.statusLabel.text = @"Login failed";
        NSLog(@"error is: %@", error);
    }
}];

但是如果账户不存在，我会收到一个错误消息：

Error Domain=com.apple.accounts Code=6 "The operation couldn’t be completed

可能是我漏掉了什么，但我并不确定该怎么做。如果您能发布一些教程或链接，介绍如何使用这个新的iOS 6功能，那就太好了，因为Facebook的教程不够清晰。

- user1832035

Answer 1

没有内置的功能来检查帐户是否存在。您应该像平常一样访问帐户，并在else分支中拦截和处理错误。错误类型是ACErrorCode，可能的值为：

typedef enum ACErrorCode {
   ACErrorUnknown = 1,
   ACErrorAccountMissingRequiredProperty,
   ACErrorAccountAuthenticationFailed,
   ACErrorAccountTypeInvalid,
   ACErrorAccountAlreadyExists,
   ACErrorAccountNotFound,
   ACErrorPermissionDenied,
   ACErrorAccessInfoInvalid
} ACErrorCode;

所以您的代码可能看起来像这样：

-(void)requestBasicPermissionsForFacebookAccount {
    ACAccountType * facebookAccountType = [self.accountStore accountTypeWithAccountTypeIdentifier:ACAccountTypeIdentifierFacebook];
    NSArray * permissions = @[@"email"];
    NSDictionary * options = @{ACFacebookAppIdKey : kFacebookAppId, ACFacebookPermissionsKey : permissions, ACFacebookAudienceKey : ACFacebookAudienceEveryone};
    FacebookAccountManager * fbMgr = [[FacebookAccountManager alloc] init];
    [self.accountStore requestAccessToAccountsWithType:facebookAccountType options:options completion:^(BOOL granted, NSError *error) {
        if (granted) {
            NSArray * accounts = [self.accountStore accountsWithAccountType:facebookAccountType];
            fbMgr.account = [accounts lastObject];
            fbMgr.isBasicPermissionsGranted = YES;
            [self.accountManagers addObject:fbMgr];
            NSLog(@"granted!");
        }
        else {
            fbMgr.account = nil;
            fbMgr.isBasicPermissionsGranted = NO;
            switch ([error code]) {
                case 1:
                    [self showErrorAlertWithMessage:@"Unknown error occured, try again later!"];
                    break;
                case 3:
                    [self showErrorAlertWithMessage:@"Authentication failed, try again later!"];
                     break;
                case 6:
                    [self showErrorAlertWithMessage:@"Facebook account does not exists. Please create it in Settings and come back!"];
                     break;
                 case 7:
                    [self showErrorAlertWithMessage:@"Permission request failed. You won't be able to share information to Facebook"];
                     break;
                default:
                    break;
            }
            NSLog(@"error is: %@", error);
        }
    }];
}

- (void)showErrorAlertWithMessage:(NSString *)message {
    dispatch_async(dispatch_get_main_queue(), ^{
        UIAlertView * alertView = [[UIAlertView alloc] initWithTitle:@"Error" message:message delegate:self cancelButtonTitle:@"Done" otherButtonTitles:nil];
        [alertView show];
    });
}

- Stas

---

为了拥有漂亮干净的代码，您可以直接在switch/case语句中使用枚举。这将使代码更加易读 :) - pro_metedor

Answer 2

使用图形 API 从该帐户名称获取详细信息并查看响应，如果不存在，则会返回错误。如需更多信息，请查看 Facebook 开发者网站 facebook。

此致

- DD_