DataGridView checkbox column - value and functionality

1. There is no way to do that directly. Once you have your data in the grid, you can loop through the rows and check each box like this:

   foreach (DataGridViewRow row in dataGridView1.Rows)
   {
       row.Cells[CheckBoxColumn1.Name].Value = true;
   }
   

2. The Click event might look something like this:

   private void button1_Click(object sender, EventArgs e)
   {
       List<DataGridViewRow> rows_with_checked_column = new List<DataGridViewRow>();
       foreach (DataGridViewRow row in dataGridView1.Rows)
       {
           if (Convert.ToBoolean(row.Cells[CheckBoxColumn1.Name].Value) == true)
           {
               rows_with_checked_column.Add(row);
           }
       }
       // Do what you want with the check rows
   }
   

it took me a long time to figure out how to do this without having to loop through all the records. I have a bound datagridview-source, and all fields are bound except for the checkbox-column. So I don't have/need a loop to add each row and I didn't want to create one just for this purpuse. So after a lot of trying I finally got it. And it's actually very simple too:

First you add a new .cs File to your project with a custom-checkbox cell, e.g.

DataGridViewCheckboxCellFilter.cs:

using System.Windows.Forms;

namespace MyNamespace {
    public class DataGridViewCheckboxCellFilter : DataGridViewCheckBoxCell {
        public DataGridViewCheckboxCellFilter() : base() {
            this.FalseValue = 0;
            this.TrueValue = 1;
            this.Value = TrueValue;
        }
    }
}

After this, on your GridView, where you add the checkbox-column, you do:

// add checkboxes
DataGridViewCheckBoxColumn col_chkbox = new DataGridViewCheckBoxColumn();
{
    col_chkbox.HeaderText = "X";
    col_chkbox.Name = "checked";
    col_chkbox.CellTemplate = new DataGridViewCheckboxCellFilter();                
}
this.Columns.Add(col_chkbox);

And that's it! Everytime your checkboxes get added in a new row, they'll be set to true. Enjoy!

private void dataGridView1_CellContentClick(object sender, DataGridViewCellEventArgs e)
{
    DataGridViewCheckBoxCell ch1 = new DataGridViewCheckBoxCell();
    ch1 = (DataGridViewCheckBoxCell)dataGridView1.Rows[dataGridView1.CurrentRow.Index].Cells[0];

    if (ch1.Value == null)
        ch1.Value=false;
    switch (ch1.Value.ToString())
    {
        case "True":
            ch1.Value = false;
            break;
        case "False":
            ch1.Value = true;
            break;
    }
    MessageBox.Show(ch1.Value.ToString());
}

best solution to find if the checkbox in the datagridview is checked or not.