datagrid

 You can handle DataGridView's CellValueChanged Event Handler

The CellValueChanged event gets fired whenever the value of a DataGridView cell is changed. Here, theRowCheckBoxClick method is invoked by passing a reference of DataGridViewCheckBoxCell that raised this event

private void dgvSelectAll_CellValueChanged(object sender, DataGridViewCellEventArgs e) { RowCheckBoxClick((DataGridViewCheckBoxCell)dgvSelectAll[e.ColumnIndex, e.RowIndex]); }

This method checks / unchecks the header CheckBox's state depending upon whether all CheckBoxes of aDataGridView column are checked or unchecked

private void RowCheckBoxClick(DataGridViewCheckBoxCell RCheckBox) {    if (RCheckBox != null)    {       //Modify Counter;                   if ((bool)RCheckBox.Value && TotalCheckedCheckBoxes < TotalCheckBoxes)          TotalCheckedCheckBoxes++;       else if (TotalCheckedCheckBoxes > 0)          TotalCheckedCheckBoxes--;        //Change state of the header CheckBox.       if (TotalCheckedCheckBoxes < TotalCheckBoxes)          HeaderCheckBox.Checked = false;       else if (TotalCheckedCheckBoxes == TotalCheckBoxes)          HeaderCheckBox.Checked = true;    } }