public AdicionarContatoViewModel()
        {
            _contatoRepositorio = new ContatoRepositorio();

            _paginaServico = new PaginaServico();

            AdicionarContatoCommand = new Command(async() => await ExecuteAdicionarContatoCommand());
        }
        public EditarContatoViewModel(Contato contatoSelecionado)
        {
            _contatoRepositorio = new ContatoRepositorio();

            _paginaServico = new PaginaServico();

            _dadosContato = contatoSelecionado;

            EditarContatoCommand  = new Command(async() => await ExecuteEditarContatoCommand());
            DeletarContatoCommand = new Command(async() => await ExecuteDeletarContatoCommand());
        }
        public ListaDeContatosViewModel()
        {
            _contatoRepositorio = new ContatoRepositorio();

            _paginaServico = new PaginaServico();

            listaDeContatos = new ObservableCollection <Contato>(ListaDeContatos());

            IrParaAdicionarContatoCommand = new Command(ExecuteIrParaAdicionarContatoCommand);
            SelecionarContatoCommand      = new Command <Contato>(async c => await ExecuteSelecionarContatoCommand(c));
        }