Facebook IOS SDK：如何进行静默登录？

Question

I have an app doing a facebook login, which works well, but everytime I reopen it I have to connect again to facebook to do the sign-in. I'm also using google sign-in sdk where I can call the function gSignIn.signInSilently() , is there something similar for facebook? I found this for the javascript sdk but I don't know if it's possible for the ios SDK and how to use it in swift...

Answer 1

The Facebook SDK automatically maintains the login state, which can be confirmed by checking for the access token.

You can check for the access using the following method:

FBSDKAccessToken.currentAccessToken()

You can check for the presence of the token which would mean that the user is logged in.

Check the docs for more details.

Answer 2

i've tried this

 if(![FBSDKAccessToken currentAccessToken])
{
    FBSDKLoginManager *manager = [[FBSDKLoginManager alloc]init];
    [manager logInWithReadPermissions:@[@"public_profile", @"email",@"user_photos"] handler:^(FBSDKLoginManagerLoginResult *result,NSError *error)
     {
         if(error == nil)
         {
             NSLog(@"Facebook - successfully login %@",result.token);
             //login successfully 
             //do your stuff here
         }
     }];
}
else
{
     //already login
     //Do Your stuff here
}

Answer 3

I am saving the access token string and manually setting it on consecutive launches to bypass the re-login flow.

func loginWithFacebook() {
    //Check for previous Access Token
    if let accessToken  = AccessToken.current {
        //AccessToken was obtained during same session
        getAccountDetails(withAccessToken: accessToken)
    }
    else if let strAuthenticationToken = UserDefaults.standard.string(forKey: "AccessToken_Facebook") {
        //A previous access token string was saved so create the required AccessToken object
        let accessToken = AccessToken(authenticationToken: strAuthenticationToken)

        //Skip Login and directly proceed to get facebook profile data with an AccessToken
        getAccountDetails(withAccessToken: accessToken)
    }
    else {
        //Access Token was not available so do the normal login flow to obtain the Access Token
        LoginManager().logIn(readPermissions: [.publicProfile, .email], viewController: nil) { loginResult in
            switch loginResult {
            case .failed(let error):
                print(error)

            case .cancelled:
                print("User cancelled login.")

            case .success(let grantedPermissions, 
                          let declinedPermissions, 
                          let accessToken):

                //Save Access Token string for silent login purpose later
                let strAuthenticationToken = accessToken.authenticationToken
                UserDefaults.standard.set(strAuthenticationToken,
                                          forKey: "AccessToken_Facebook")

                //Proceed to get facebook profile data
                self.getAccountDetails(withAccessToken: accessToken)
            }
        }
    }
}

---

func getAccountDetails(withAccessToken accessToken: AccessToken) {
    let graphRequest: GraphRequest = GraphRequest(graphPath     : "me",
                                                  parameters    : ["fields" : "id, name, email"],
                                                  accessToken   : accessToken,
                                                  httpMethod    : GraphRequestHTTPMethod.GET,
                                                  apiVersion    : GraphAPIVersion.defaultVersion)
    graphRequest.start { (response, result) in
        switch result {
        case .success(let resultResponse):
            print(resultResponse)
        case .failed(let error):
            print(error)
        }
    }
}

NOTE: For the ease of this example, the Facebook Access Token string is being saved to UserDefaults but ideally it should be saved to the Keychain.

(Swift 4 / Facebook SDK 4.30)