iOS Facebook 登录 - 链接器错误

Question

我正在尝试在我的应用程序中实现 facebook 登录，我严格遵循了这两个指南:

http://developers.facebook.com/docs/getting-started/facebook-sdk-for-ios/ https://developers.facebook.com/docs/howtos/login-with-facebook-using-ios-sdk/

但是当我尝试为 iPhone 模拟器编译应用程序时，出现链接器错误。

Undefined symbols for architecture i386:
  "_FBSessionStateChangedNotification", referenced from:
      -[AppDelegate sessionStateChanged:state:error:] in AppDelegate.o
      -[LoginViewController viewDidLoad] in LoginViewController.o
      -[AppDelegate sessionStateChanged:state:error:] in AppDelegate.o
      -[LoginViewController viewDidLoad] in LoginViewController.o
ld: symbol(s) not found for architecture i386

我已确保所有必要的框架和文件都位于正确的位置。另外，我在 Xcode 中没有收到任何代码错误，所以我真的不知道这里出了什么问题。

拜托，非常感谢任何帮助。

---

编辑:

//AppDelegate.h

#import <UIKit/UIKit.h>
#import <FacebookSDK/FacebookSDK.h>

@interface AppDelegate : UIResponder <UIApplicationDelegate> {

}

@property (strong, nonatomic) UIWindow *window;

extern NSString *const FBSessionStateChangedNotification;
- (BOOL)openSessionWithAllowLoginUI:(BOOL)allowLoginUI;
- (void)closeSession;
@end

-

//  AppDelegate.m

#import "AppDelegate.h"
#import "NetworkCheck.h"


@implementation AppDelegate

- (void)dealloc
{
    [_window release];
    [super dealloc];
}

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // Override point for customization after application launch.
    NSLog(@"Application launch");

    NetworkCheck *netCheck = [[NetworkCheck alloc] init];
    [netCheck startCheck];

    NSString *const FBSessionStateChangedNotification =     @"com.example.Login:FBSessionStateChangedNotification";


    return YES;
}

/*
 * If we have a valid session at the time of openURL call, we handle
 * Facebook transitions by passing the url argument to handleOpenURL
 */
- (BOOL)application:(UIApplication *)application
            openURL:(NSURL *)url
  sourceApplication:(NSString *)sourceApplication
         annotation:(id)annotation {
    // attempt to extract a token from the url
    return [FBSession.activeSession handleOpenURL:url];
}

/*
 * Callback for session changes.
 */
- (void)sessionStateChanged:(FBSession *)session
                  state:(FBSessionState) state
                  error:(NSError *)error
{
    switch (state) {
        case FBSessionStateOpen:
            if (!error) {
                // We have a valid session
                NSLog(@"User session found");
            }
            break;
        case FBSessionStateClosed:
        case FBSessionStateClosedLoginFailed:[FBSession.activeSession closeAndClearTokenInformation];
            break;
        default:
            break;
    }

[[NSNotificationCenter defaultCenter]
 postNotificationName:FBSessionStateChangedNotification
 object:session];

if (error) {
    UIAlertView *alertView = [[UIAlertView alloc]
                              initWithTitle:@"Error"
                              message:error.localizedDescription
                              delegate:nil
                              cancelButtonTitle:@"OK"
                              otherButtonTitles:nil];
    [alertView show];
}
}

/*
 * Opens a Facebook session and optionally shows the login UX.
 */
- (BOOL)openSessionWithAllowLoginUI:(BOOL)allowLoginUI {
return [FBSession openActiveSessionWithReadPermissions:nil
                                          allowLoginUI:allowLoginUI
                                     completionHandler:^(FBSession *session,
                                                         FBSessionState state,
                                                         NSError *error) {
                                         [self sessionStateChanged:session
                                                             state:state
                                                             error:error];
                                     }];
}

- (void) closeSession {
[FBSession.activeSession closeAndClearTokenInformation];
}

- (void)applicationWillResignActive:(UIApplication *)application
{
// Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
// Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
}

- (void)applicationDidEnterBackground:(UIApplication *)application
{
// Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later. 
// If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
}

- (void)applicationWillEnterForeground:(UIApplication *)application
{
// Called as part of the transition from the background to the inactive state; here you     can undo many of the changes made on entering the background.
}

- (void)applicationDidBecomeActive:(UIApplication *)application
{
// Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.

// We need to properly handle activation of the application with regards to Facebook Login
// (e.g., returning from iOS 6.0 Login Dialog or from fast app switching).
[FBSession.activeSession handleDidBecomeActive];
}

- (void)applicationWillTerminate:(UIApplication *)application
{
// Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
[FBSession.activeSession close];
}

@end

Answer 1

FBSessionStateChangedNotification 是一个 extern 定义，它应该在您导入的任何头文件中可见，以便您在 appDelegate 中编写的代码可以访问。

您需要转接此行:

NSString *const FBSessionStateChangedNotification = @"com.example.Login:FBSessionStateChangedNotification";

到一个文件，使其对其他类(不仅仅是应用程序委托(delegate))可见。