Connecting three datagridviews using checkbox selection

This turned out to be more fiddly than I expected!

Choosing the appropriate event to put code behind was the first problem. CellValidated or CellValueChanged were my first thoughts, but these were not being fired when I expected (for example CellValidated is not fired when the checkbox is clicked, but when you click elsewhere - not a good user experience)

I ended up choosing the dataGridView2_CellClick event, which brings it's own problems ... when checking the .Value of the cell on the first click you will find it is null. So I had to use EditingCellFormattedValue instead - trouble is, at the time the event is fired this value is still the opposite of what we think it is ... in other words when we are clicking the tick box this value is still false - it has the value we are moving from not the value we are moving to. I'm labouring this point a little to draw attention to the not (!) operator in the line

var checkValue = !(bool)((DataGridViewCheckBoxCell)dataGridView2.Rows[r].Cells[c]).EditingCellFormattedValue;

The next issue to consider is whether or not the properties AllowUserToAddRows has been set to true or false (the default is true). In the code below I handle either, but if you omit the setting of this to false when using the foreach you will get an exception

Quote:

An unhandled exception of type 'System.NullReferenceException' occurred in Sandbox.exe

Additional information: Object reference not set to an instance of an object.

Here is my full solution

private void dataGridView2_CellClick(object sender, DataGridViewCellEventArgs e)
{
    var r = e.RowIndex;
    var c = e.ColumnIndex;

    if (dataGridView2.Rows[r].Cells[c].GetType() != typeof(DataGridViewCheckBoxCell)) return;

    var procodSearch = dataGridView2.Rows[r].Cells[2].Value.ToString();
    var typcodSearch = dataGridView2.Rows[r].Cells[3].Value.ToString();
    var checkValue = !(bool)((DataGridViewCheckBoxCell)dataGridView2.Rows[r].Cells[c]).EditingCellFormattedValue;

    var temp = dataGridView1.AllowUserToAddRows;
    dataGridView1.AllowUserToAddRows = false;

    foreach (DataGridViewRow dr in dataGridView1.Rows)
    {
        if (dr.Cells[dataGridView1.Columns["procod"].Index].Value.ToString().Equals(procodSearch)
            && dr.Cells[dataGridView1.Columns["typcod"].Index].Value.ToString().Equals(typcodSearch))
            ((DataGridViewCheckBoxCell)dr.Cells[0]).Value = checkValue;
    }
    dataGridView1.AllowUserToAddRows = temp;

    temp = dataGridView3.AllowUserToAddRows;
    dataGridView3.AllowUserToAddRows = false;

    foreach (DataGridViewRow dr in dataGridView3.Rows)
    {
        if (dr.Cells[dataGridView3.Columns["typcod"].Index].Value.ToString().Equals(typcodSearch))
            ((DataGridViewCheckBoxCell)dr.Cells[0]).Value = checkValue;
    }
    dataGridView3.AllowUserToAddRows = temp;

}

Or if you prefer to use Linq:

private void dataGridView2_CellClick(object sender, DataGridViewCellEventArgs e)
{
    var r = e.RowIndex;
    var c = e.ColumnIndex;

    if (dataGridView2.Rows[r].Cells[c].GetType() != typeof(DataGridViewCheckBoxCell)) return;

    var procodSearch = dataGridView2.Rows[r].Cells["procod"].Value.ToString();
    var typcodSearch = dataGridView2.Rows[r].Cells["typcod"].Value.ToString();
    var checkValue = !(bool)((DataGridViewCheckBoxCell)dataGridView2.Rows[r].Cells[c]).EditingCellFormattedValue;

    var temp = dataGridView1.AllowUserToAddRows;
    dataGridView1.AllowUserToAddRows = false;

    foreach (DataGridViewRow dr in dataGridView1.Rows.Cast<DataGridViewRow>()
        .Where(dr => dr.Cells[dataGridView1.Columns["procod"].Index].Value.ToString().Equals(procodSearch)
           && dr.Cells[dataGridView1.Columns["typcod"].Index].Value.ToString().Equals(typcodSearch)))
        ((DataGridViewCheckBoxCell)dr.Cells[0]).Value = checkValue;

    dataGridView1.AllowUserToAddRows = temp;

    temp = dataGridView3.AllowUserToAddRows;
    dataGridView3.AllowUserToAddRows = false;

    foreach (DataGridViewRow dr in dataGridView3.Rows.Cast<DataGridViewRow>()
        .Where(dr => dr.Cells[dataGridView3.Columns["typcod"].Index].Value.ToString().Equals(typcodSearch)))
        ((DataGridViewCheckBoxCell)dr.Cells[0]).Value = checkValue;

    dataGridView3.AllowUserToAddRows = temp;

}

This is not an ideal solution - for example I have made some assumptions about which columns contain the CheckBoxes (I've assumed column 0 above) and there is no checking for null values in any columns, but it's a start.