您可以尝试使用此

 _googleSignIn.signIn().then((result){
          result.authentication.then((googleKey){
              print(googleKey.accessToken);
              print(googleKey.idToken);
              print(_googleSignIn.currentUser.displayName);
          }).catchError((err){
            print('inner error');
          });
      }).catchError((err){
          print('error occured');
      });