How come additional rows aren't being shown when button is clicked in DataGridView?

Question

This is my code:

namespace UpdateDataGridView
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        List<Apple> apples = new List<Apple>();

        private void button1_Click(object sender, EventArgs e)
        {
            apples.Add(new Apple { Color = "Red"});
            dataGridView1.DataSource = apples;
        }
    }
    public class Apple
    {
        public string Color { get; set; }
    }
}

I am expecting a new row to be added to the dataridview every time the button is pressed.

I am not sure why this is not happening and I don't know how to achieve this. Any help is much appreciated.

Answer 1

You need to emit event for datagrid redraw. The simplest way, if your DataSource isn't big is next:

private void button1_Click(object sender, EventArgs e)
    {
        apples.Add(new Apple { Color = "Red"});
        dataGridView1.DataSource = null;
        dataGridView1.DataSource = apples;
    }

If your collection is too big, you'd better to change your container from List to ObservableCollection

ObservableCollection<Apple> apples = new ObservableCollection<Apple>();

    private void button1_Click(object sender, EventArgs e)
    {
        apples.Add(new Apple { Color = "Red"});
        dataGridView1.DataSource = apples;
    }

In your code, you can use ObservableCollection just like List, but it will tell your datagrid about changing items in your apples container

Answer 2

Like many UI frameworks, Forms does not automatically redraw itself - it therefore must be told (often explicitly) when data has been changed and that it needs to refresh. Try calling datagridview1.Refresh() at the end of your event handler.