How to pass datagridview object to another newly created form?

Question

I'm following this SO post to pass DataGridView to second form, so I can access cells to paint them based on values..

In Form1 I'm creating that DataGridView as below :

namespace LightnessComparision
{

    public partial class Form1 : Form
    {
        public DataGridView dgv = new DataGridView
        {
            Name = "LightnessGrid",
            Visible = true,
            DataSource = null,
            AutoSize = true,
            RowHeadersVisible = false,
            ColumnHeadersVisible = false,
            ScrollBars = ScrollBars.Both,
            AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.DisplayedCellsExceptHeader,
    };

/* Public Form1 etc */

        public void Button3_Click(object sender, EventArgs e)
        {
 /* SOME LOGIC */

            LightnessTable LightnessForm = new LightnessTable();
            dgv.DataSource = resulTable;
            LightnessForm.dgv = dgv;
            LightnessForm.Controls.Add(dgv);
            LightnessForm.AutoSize = true;
            LightnessForm.Show();     
        }
    }
}

LightnessTable which is Form looks like :

namespace LightnessComparision
{
    public partial class LightnessTable : Form
    {
        public DataGridView dgv { get; set; }
        public LightnessTable()
        {
            InitializeComponent();
            DataGridView_Configuration();
        }
        private void DataGridView_Configuration()
        {
            dgv.VisibleChanged += DgView_VisibleChanged;
        }
        private void DgView_VisibleChanged(object sender, EventArgs e)
        {
            DataGridView_PaintCells();
        }
        private void DataGridView_PaintCells()
        {
            foreach (DataGridViewRow row in dgv.Rows)
            {
                foreach (DataGridViewCell cell in row.Cells)
                {
                    if (Convert.ToInt16(cell.Value) < -5)
                    {
                        cell.Style.BackColor = Color.Yellow;
                    }
                    if (Convert.ToInt16(cell.Value) > 5)
                    {
                        cell.Style.BackColor = Color.Black;
                    }
                }
            }
        }

    }
}

However dgv.VisibleChanged += DgView_VisibleChanged; this line throws me error that dgv is null.

What's wrong here?

Answer 1

You call dgv.VisibleChanged += DgView_VisibleChanged; in constructor (throughDataGridView_Configuration()call), but for this moment dgv is not initialized yet.

Consider to pass DataGridView as constructor parameter:

    public LightnessTable(DataGridView dgv)
    {
        InitializeComponent();
        this.dgv = dgv; 
        Controls.Add(this.dgv);
        DataGridView_Configuration();
    }

and change the call:

    public void Button3_Click(object sender, EventArgs e)
    {
        /* SOME LOGIC */

        dgv.DataSource = resulTable;
        LightnessTable LightnessForm = new LightnessTable(dgv);            
        LightnessForm.AutoSize = true;
        LightnessForm.Show();     
    }

Also I moved Controls.Add(dgv); into the form constructor - it is not necessary, but looks more logical.

Answer 2

You are calling DataGridView_Configuration() from LightnessTable constructor, so dgv is still null.