UIActionSheetでtwitterアカウントを選択させる

_accounts = [_accountStore accountsWithAccountType:_accountType];

-(void)showActionSheet {
    UIActionSheet *sheet = [[UIActionSheet alloc] init];
    [sheet setDelegate:(id)self];
    for (int i = 0; i < _accounts.count; i++) {
        [sheet addButtonWithTitle:[_accounts[i] valueForKey:@"username"]];
    }
    [sheet showInView:self.view];
}

-(void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex {
    _currentAccount = _accounts[buttonIndex];
}