C# - DataGridView can't add row?

Question

I have a simple C# Windows Forms application which should display a DataGridView. As DataBinding I used an Object (selected a class called Car) and this is what it looks like:

class Car
{
    public string color { get; set ; }
    public int maxspeed { get; set; }

    public Car (string color, int maxspeed) {
        this.color = color;
        this.maxspeed = maxspeed;
    }
}

However, when I set the DataGridView property AllowUserToAddRows to true , there is still no little * which allows me to add rows.

Someone suggested to set carBindingSource.AllowAdd to true , however, when I do that, I get a MissingMethodException which says my constructor could not be found.

Answer 1

Your Car class needs to have a parameterless constructor and your datasource needs be something like a BindingList

Change the Car class to this:

class Car
{
    public string color { get; set ; }
    public int maxspeed { get; set; }

    public Car() {
    }

    public Car (string color, int maxspeed) {
        this.color = color;
        this.maxspeed = maxspeed;
    }
}

And then bind something like this:

BindingList<Car> carList = new BindingList<Car>();

dataGridView1.DataSource = carList;

You can also use a BindingSource for this, you don't have to but BindingSource gives some extra functionality that can sometimes be necessary.

---

If for some reason you absolutely cannot add the parameterless constructor then you can handle the adding new event of the binding source and call the Car parameterised constructor:

Setting up the binding:

BindingList<Car> carList = new BindingList<Car>();
BindingSource bs = new BindingSource();
bs.DataSource = carList;
bs.AddingNew +=
    new AddingNewEventHandler(bindingSource_AddingNew);

bs.AllowNew = true;
dataGridView1.DataSource = bs;

And the handler code:

void bindingSource_AddingNew(object sender, AddingNewEventArgs e)
{
    e.NewObject = new Car("",0);
}

Answer 2

You need to add AddingNew event handler:

public partial class Form1 : Form
{
    private BindingSource carBindingSource = new BindingSource();



    public Form1()
    {
        InitializeComponent();
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        dataGridView1.DataSource = carBindingSource;

        this.carBindingSource.AddingNew +=
        new AddingNewEventHandler(carBindingSource_AddingNew);

        carBindingSource.AllowNew = true;



    }

    void carBindingSource_AddingNew(object sender, AddingNewEventArgs e)
    {
        e.NewObject = new Car();
    }
}

Answer 3

I recently discovered that if you implement your own binding list using IBindingList you MUST return true in your SupportsChangeNotification in addition to AllowNew .

The MSDN article for DataGridView.AllowUserToAddRows only specifies the following remark however:

If the DataGridView is bound to data, the user is allowed to add rows if both this property and the data source's IBindingList.AllowNew property are set to true.