How can I allow insertion directly into a Datagridview?

Question

I am setting the DataSource of a DataGridView with a List<T>. I enabled by designer "enable addition".

But there is not appearing that line with asterisk for adding new elements.

My code is like this:

public IEnumerable<Valor> Valores
{
    get;
    set;
}

private void Form1_Load(object sender, EventArgs ev)
{
    if (Valores == null)
    {
        Valores = new List<Valor>();
    }

    dataGrid.DataSource = Valores;
}

Answer 1

The problem is you’re trying to put a List<T> in the DataSource, however a list does not have the resources to connect the screen component with the property.

Instead of using a List<T> use a BindingList<T>. This type provides two-way Binding, that is, what you add through the grid will be added to the object, and what is added to the object will be added to the grid.

BindingList<T> implements the interface IBindingList containing the property AllowNew. This property will be false when there is no default constructor for T.

As an example:

public class Pessoa
{
    public string Nome { get; set; }
    public int Idade { get; set; }
}

When the constructor is empty or omitted (with no other) it means that you have a default constructor. In this case your grid will show the field to insert a new element.

public BindingList<Pessoa> lista = new BindingList<Pessoa>
{
    new Pessoa { Idade = 20, Nome = "Teste 1" },
    new Pessoa { Idade = 22, Nome = "Teste 2" },
    new Pessoa { Idade = 23, Nome = "Teste 3" },
};

However, if your class does not have a standard constructor:

public class Pessoa
{
    public string Nome { get; set; }
    public int Idade { get; set; }
    public Pessoa(int x) { }
}

---

If you need to use a List<T>, you can create a BindingList<T> from the list, start a property of your form with:

ListaBinding = new BindingList<Pessoa>( new List<Pessoa>() );

Use this list to work with the grid and then you can pass the data you want to your other list.