ボタンアクションからAppDelegateでメソッドを呼び出すときにエラーを取得します。

Question

「保存」をクリックすると、AppDelegateに話しかけたときにエラーが発生します。

私はここで小さなものが足りないと確信していますが、誰かが簡単な答えを持っているなら、それは大歓迎です。

これが私が得ているエラーです：

-[AppDelegate saveNewUsername:username:]: unrecognized selector sent to instance 0x8e403d0

これが私のボタンアクションです：

-(IBAction)saveButtonPressed:(id)sender
{
AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];

NSString *userid = [appDelegate retrieveFromUserDefaults:@"userid"];
NSMutableArray *currentUser = [appDelegate getUserInfo:userid];
NSString *currentUsername = [currentUser objectAtIndex:0];

NSLog(@"%@", userid);

if ([currUsername.text isEqualToString:currentUsername]) {
    //here we'll check and make sure the new username is valid and doesn't already exist (for now just update local DB)
    if ([theNewUsername.text isEqualToString:@""]) {
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"" message:@"You must enter something for your new username." delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil, nil];
        [alert show];
    } else {
        int returnVal = [appDelegate saveNewUsername:userid username:theNewUsername.text];
        if (returnVal == 1) {
            [self dismissModalViewControllerAnimated:YES];
        } else {
            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error" message:@"There was an error saving to the database." delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil, nil];
            [alert show];
        }
    }
} else {
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"" message:@"The username you entered is not your current username." delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil, nil];
    [alert show];
}
}

そして、これが私のAppDelegateの方法です：

-(int)saveNewUsername:(NSString *)user_id username:(NSString *)username
{
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0]; 
NSString *writableDBPath = [documentsDirectory stringByAppendingPathComponent:@"somedbname.sqlite3"];

FMDatabase *db = [FMDatabase databaseWithPath:writableDBPath];

if (![db open]) {
    NSLog(@"Could not open db.");
    return 0;
} else {
    [db intForQuery:@"UPDATE user SET username=? WHERE user_id=?", username, user_id];

    if ([db hadError]) {
        NSLog(@"Error %d: %@", [db lastErrorCode], [db lastErrorMessage]);
        return 0;
    } else {
        return 1;
    }
}
}