Check/Uncheck a checkbox on datagridview

Looking at this MSDN Forum Posting it suggests comparing the Cell's value with Cell.TrueValue.

So going by its example your code should looks something like this:(this is completely untested)

Edit: it seems that the Default for Cell.TrueValue for an Unbound DataGridViewCheckBox is null you will need to set it in the Column definition.

private void chkItems_CheckedChanged(object sender, EventArgs e)
{
    foreach (DataGridViewRow row in dataGridView1.Rows)
    {
        DataGridViewCheckBoxCell chk = (DataGridViewCheckBoxCell)row.Cells[1];
        if (chk.Value  == chk.TrueValue)
        {
            chk.Value = chk.FalseValue;
        }
        else
        {
            chk.Value = chk.TrueValue;
        }
    }
}

---

This code is working note setting the TrueValue and FalseValue in the Constructor plus also checking for null:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        DataGridViewCheckBoxColumn CheckboxColumn = new DataGridViewCheckBoxColumn();
        CheckboxColumn.TrueValue = true;
        CheckboxColumn.FalseValue = false;
        CheckboxColumn.Width = 100;
        dataGridView1.Columns.Add(CheckboxColumn);
        dataGridView1.Rows.Add(4);
    }

    private void chkItems_CheckedChanged(object sender, EventArgs e)
    {
        foreach (DataGridViewRow row in dataGridView1.Rows)
        {
            DataGridViewCheckBoxCell chk = (DataGridViewCheckBoxCell)row.Cells[0];
            if (chk.Value == chk.FalseValue || chk.Value == null)
            {
                chk.Value = chk.TrueValue;
            }
            else
            {
                chk.Value = chk.FalseValue;
            }

        }
        dataGridView1.EndEdit();
    }
}

Simple code for you it will work

private void dgv_CellClick(object sender, DataGridViewCellEventArgs e)
{
    if (dgv.CurrentRow.Cells["ColumnNumber"].Value != null && (bool)dgv.CurrentRow.Cells["ColumnNumber"].Value)
    {
        dgv.CurrentRow.Cells["ColumnNumber"].Value = false;
        dgv.CurrentRow.Cells["ColumnNumber"].Value = null;
    }
    else if (dgv.CurrentRow.Cells["ColumnNumber"].Value == null )
    {
        dgv.CurrentRow.Cells["ColumnNumber"].Value = true;
    }
}

I was making my own version of a Checkbox to control a DataGridViewCheckBoxColumn when I saw this post wasn't actually answered. To set the checked state of a DataGridViewCheckBoxCell use:

foreach (DataGridViewRow row in dataGridView1.Rows)
{
    dataGridView1.Rows[row.Index].SetValues(true);
}

For anyone else trying to accomplish the same thing, here is what I came up with.

This makes the two controls behave like the checkbox column in Gmail. It keeps functionality for both mouse and keyboard.

using System;
using System.Windows.Forms;

namespace Check_UnCheck_All
{
    public partial class Check_UnCheck_All : Form
    {
        public Check_UnCheck_All()
        {
            InitializeComponent();
            dataGridView1.RowCount = 10;
            dataGridView1.AllowUserToAddRows = false;
            this.dataGridView1.CellContentClick += new System.Windows.Forms.DataGridViewCellEventHandler(this.dgvApps_CellContentClick);
            this.dataGridView1.CellMouseUp += new System.Windows.Forms.DataGridViewCellMouseEventHandler(this.myDataGrid_OnCellMouseUp);
            this.dataGridView1.CellValueChanged += new System.Windows.Forms.DataGridViewCellEventHandler(this.myDataGrid_OnCellValueChanged);
            this.checkBox1.Click += new System.EventHandler(this.checkBox1_Click);
        }

        public int chkInt = 0;
        public bool chked = false;

        public void myDataGrid_OnCellValueChanged(object sender, DataGridViewCellEventArgs e)
        {
            if (e.ColumnIndex == dataGridView1.Rows[0].Index && e.RowIndex != -1)
            {
                DataGridViewCheckBoxCell chk = dataGridView1.Rows[e.RowIndex].Cells[0] as DataGridViewCheckBoxCell;

                if (Convert.ToBoolean(chk.Value) == true) chkInt++;
                if (Convert.ToBoolean(chk.Value) == false) chkInt--;
                if (chkInt < dataGridView1.Rows.Count && chkInt > 0)
                {
                    checkBox1.CheckState = CheckState.Indeterminate;
                    chked = true;
                }
                else if (chkInt == 0)
                {
                    checkBox1.CheckState = CheckState.Unchecked;
                    chked = false;
                }
                else if (chkInt == dataGridView1.Rows.Count)
                {
                    checkBox1.CheckState = CheckState.Checked;
                    chked = true;
                }
            }
        }
        public void myDataGrid_OnCellMouseUp(object sender, DataGridViewCellMouseEventArgs e)
        {
            // End of edition on each click on column of checkbox
            if (e.ColumnIndex == dataGridView1.Rows[0].Index && e.RowIndex != -1)
            {
                dataGridView1.EndEdit();
            }
            dataGridView1.BeginEdit(true);
        }
        public void dgvApps_CellContentClick(object sender, DataGridViewCellEventArgs e)
        {
            if (dataGridView1.CurrentCell.GetType() == typeof(DataGridViewCheckBoxCell))
            {
                if (dataGridView1.CurrentCell.IsInEditMode)
                {
                    if (dataGridView1.IsCurrentCellDirty)
                    {
                        dataGridView1.EndEdit();
                    }
                }
                dataGridView1.BeginEdit(true);
            }
        }
        public void checkBox1_Click(object sender, EventArgs e)
        {
            if (chked == true)
            {
                foreach (DataGridViewRow row in dataGridView1.Rows)
                {
                    DataGridViewCheckBoxCell chk = (DataGridViewCheckBoxCell)row.Cells[0];
                    if (chk.Value == chk.TrueValue)
                    {
                        chk.Value = chk.FalseValue;
                    }
                    else
                    {
                        chk.Value = chk.TrueValue;
                    }
                }
                chked = false;
                chkInt = 0;
                return;
            }
            if (chked == false)
            {
                foreach (DataGridViewRow row in dataGridView1.Rows)
                {
                    dataGridView1.Rows[row.Index].SetValues(true);
                }
                chked = true;
                chkInt = dataGridView1.Rows.Count;
            }
        }
    }
}