C#

private void Form1_Load(object sender, EventArgs e)
{
    DataTable mainData = new DataTable("mainData");
    mainData.Columns.Add("ID", typeof(int));
    mainData.Columns.Add("ValueType", typeof(int));
    mainData.Columns.Add("ValueUnitOfMeasurement", typeof(int));
    mainData.Columns.Add("TheValue", typeof(decimal));

    DataTable valueType = new DataTable("valueType");
    valueType.Columns.Add("ID", typeof(int)); // should be like a primary key
    valueType.Columns.Add("Description", typeof(string));

    DataTable valueUnitOfMeasurement = new DataTable("valueUnitOfMeasurement");
    valueUnitOfMeasurement.Columns.Add("ID", typeof(int)); // should be like a primary key
    valueUnitOfMeasurement.Columns.Add("ValueTypeID", typeof(int));
    valueUnitOfMeasurement.Columns.Add("Description", typeof(string));

    valueType.Rows.Add(new object[] { 1, "Force" });
    valueType.Rows.Add(new object[] { 2, "Torque" });
    valueType.Rows.Add(new object[] { 3, "Pressure" });

    valueUnitOfMeasurement.Rows.Add(new object[] { 1, 1, "lb"});
    valueUnitOfMeasurement.Rows.Add(new object[] { 2, 1, "N" });
    valueUnitOfMeasurement.Rows.Add(new object[] { 3, 2, "N-m" });
    valueUnitOfMeasurement.Rows.Add(new object[] { 4, 2, "in-lb" });
    valueUnitOfMeasurement.Rows.Add(new object[] { 5, 3, "Pa" });
    valueUnitOfMeasurement.Rows.Add(new object[] { 6, 3, "bar" });


    dataGridView1.AutoGenerateColumns = false;
    dataGridView1.DataSource = mainData;

    valueTypeColumn.DataSource = valueType;
    valueTypeColumn.ValueMember = "ID";
    valueTypeColumn.DisplayMember = "Description";

    myBinding.DataSource = valueUnitOfMeasurement;
    valueUnitOfMeasurementColumn.DataSource = myBinding;
    valueUnitOfMeasurementColumn.ValueMember = "ID";
    valueUnitOfMeasurementColumn.DisplayMember = "Description";

    dataGridView1.EditingControlShowing += new DataGridViewEditingControlShowingEventHandler(dataGridView1_EditingControlShowing);
    dataGridView1.RowValidated += new DataGridViewCellEventHandler(dataGridView1_RowValidated);
}

void dataGridView1_RowValidated(object sender, DataGridViewCellEventArgs e)
{
    myBinding.Filter = string.Empty; // reset the filter
}

void dataGridView1_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
{
    if (e.Control is ComboBox) // if the editing control is a comboBox
    {
        ComboBox editingControl = e.Control as ComboBox;

        // check if the comboBox is the one binded to the binding source
        if (editingControl.DataSource is BindingSource)
        {
            if ((editingControl.DataSource as BindingSource).Equals(myBinding))
            {
                // this control is binded to the bindingSource, so let's filter the binding source

                if(dataGridView1.CurrentRow == null)
                    return;

                int selectedID;
                bool ok = Int32.TryParse(Convert.ToString(dataGridView1.CurrentRow.Cells["valueTypeColumn"].Value), out selectedID);

                if (ok) // do the filter
                    myBinding.Filter = "ValueTypeID = " + selectedID;
                else // no value selected
                    myBinding.Filter = "ValueTypeID = -1"; // show nothing


                return;
            }
        }
    }
}

Stanciu Vlad wrote:

DataTable mainData = new DataTable("mainData");
mainData.Columns.Add("ID", typeof(int));
mainData.Columns.Add("ValueType", typeof(int));
mainData.Columns.Add("ValueUnitOfMeasurement", typeof(int));
mainData.Columns.Add("TheValue", typeof(decimal));

valueType.Rows.Add(new object[] {100, "Distance"});

valueType.Rows.Add(new object[] {500, 100, "km"});
valueUnitOfMeasurement.Rows.Add(new object[] {501, 100, "m"});
valueUnitOfMeasurement.Rows.Add(new object[] {502, 100, "cm"});
valueUnitOfMeasurement.Rows.Add(new object[] {503, 100, "mm"});

public partial class Form1 : Form
    {
        DataTable tblPrimary, tblSecondary;
        BindingSource primaryBS, filteredSecondaryBS, unfilteredSecondaryBS;
        
        public Form1()
        {

            tblPrimary = new DataTable("Primary");
            tblPrimary.Columns.Add("ID", typeof(int));
            tblPrimary.Columns.Add("Name", typeof(string));

            tblSecondary = new DataTable("Secondary");
            tblSecondary.Columns.Add("ID", typeof(int));
            tblSecondary.Columns.Add("subID", typeof(int));
            tblSecondary.Columns.Add("Name", typeof(string));

            tblPrimary.Rows.Add(new object[] { 0, "Force" });
            tblPrimary.Rows.Add(new object[] { 1, "Torque" });
            tblPrimary.Rows.Add(new object[] { 2, "Pressure" });

            tblSecondary.Rows.Add(new object[] { 0, 0, "lb" });
            tblSecondary.Rows.Add(new object[] { 1, 0, "N" });
            tblSecondary.Rows.Add(new object[] { 2, 0, "oz" });
            tblSecondary.Rows.Add(new object[] { 3, 1, "in-lb" });
            tblSecondary.Rows.Add(new object[] { 4, 1, "ft-lb" });
            tblSecondary.Rows.Add(new object[] { 5, 1, "N-m" });
            tblSecondary.Rows.Add(new object[] { 6, 2, "PSI" });
            tblSecondary.Rows.Add(new object[] { 7, 2, "Pa" });
            tblSecondary.Rows.Add(new object[] { 8, 2, "bar" });
            
            InitializeComponent();

            primaryBS = new BindingSource();
            primaryBS.DataSource = tblPrimary;
            primaryComboBoxColumn.DataSource = primaryBS;
            primaryComboBoxColumn.DisplayMember = "Name";
            primaryComboBoxColumn.ValueMember = "ID";

            // the ComboBox column is bound to the unfiltered DataView
            unfilteredSecondaryBS = new BindingSource();
            DataView undv = new DataView(tblSecondary);
            unfilteredSecondaryBS.DataSource = undv;
            secondaryComboBoxColumn.DataSource = unfilteredSecondaryBS;
            secondaryComboBoxColumn.DisplayMember = "Name";
            secondaryComboBoxColumn.ValueMember = "ID";

            // this binding source is where I perform my filtered view
            filteredSecondaryBS = new BindingSource();
            DataView dv = new DataView(tblSecondary);
            filteredSecondaryBS.DataSource = dv;
        }
                

       
        private void dataGridView1_CellBeginEdit(object sender, DataGridViewCellCancelEventArgs e)
        {
                if (e.ColumnIndex == secondaryComboBoxColumn.Index)
                {
                    DataGridViewComboBoxCell dgcb = (DataGridViewComboBoxCell)dataGridView1[e.ColumnIndex, e.RowIndex];
                    dgcb.DataSource = filteredSecondaryBS;

                    this.filteredSecondaryBS.Filter = "subid = " +
                        this.dataGridView1[e.ColumnIndex - 1, e.RowIndex].Value.ToString();
                }
            
         }

        private void dataGridView1_CellEndEdit(object sender, DataGridViewCellEventArgs e)
        {
           
                if (e.ColumnIndex == this.secondaryComboBoxColumn.Index)
                {
                    DataGridViewComboBoxCell dgcb = (DataGridViewComboBoxCell)dataGridView1[e.ColumnIndex, e.RowIndex];
                    dgcb.DataSource = unfilteredSecondaryBS;

                    this.filteredSecondaryBS.RemoveFilter();
                }
        
        }

SELECT @@rowcount AS 'RowsChanged'