Quite simple actually ... in the OnStart method, simply throw an exception.

from a solution provided by Alexandre Palma in Message #1187639

// wrong way to do it
foreach(DataRow loRow in DataTable.Rows)
{
    if (loRow["MyField"] = string.Empty)
    {
        loRow.RejectChanges();
    }
}

// right way to do it
for(int i = myTable.Rows.Count-1; i >= 0; i--)
{
    if ((string)myTable.Rows[i]["MyField"] == String.Empty)
    {
        myTable.Rows[i].RejectChanges();
    }
}

from a solution provided by Çetin Basöz in Message #1251872

TextBox1.Attributes.Add("onkeydown", 
	"if(event.which || event.keyCode)
		{if ((event.which == 13) || (event.keyCode == 13)) 
			{document.getElementById('"+Button1.UniqueID+"').click();return false;}} 
	else {return true}; ");

from a solution provided by Mike Cole in Message #1203026

Let's use an example to illustrate this ... we'd like our Control to hook into the Form's Load and Closing events. Let's use the ListView as an example. First, we'll sub-class the ListView Control. As you can see we override the OnParentChanged event in the ListView sub-class.

We utilize the TopLevelControl (not the Parent). If the TopLevelControl is null then we hookup event handlers backwards through the control hierarchy as each control is parented. When we finally get to a TopLevelControl for a Form type we hookup the load/close event handlers.

public class MyListView : System.Windows.Forms.ListView
{
   private Form _parentForm = null;

   public MyListView()
   {
   }

   protected override void OnParentChanged(EventArgs e)
   {
      base.OnParentChanged(e);
			
      if (this._parentForm != null)
         return;

      if (this.DesignMode == false)
      {
         if (this.TopLevelControl != null && this.TopLevelControl is Form)
         {
            this._parentForm = (Form)this.TopLevelControl;
            this.EstablishParentEvents();
         }
         else
         {
            Control LastParent = this;

            while(LastParent != null)
            {
               LastParent.ParentChanged += new EventHandler(LastParent_ParentChanged);
               LastParent = LastParent.Parent;
            }
         }
      }
   }

   private void EstablishParentEvents()
   {
      this._parentForm.Closing += new CancelEventHandler(MyListView_Closing);
      this._parentForm.Load += new EventHandler(MyListView_Load);
   }

   private void MyListView_Closing(object sender, CancelEventArgs e)
   {
      MessageBox.Show("The parent form is closing!");

      if (this._parentForm != null)
      {
         this._parentForm.Closing -= new CancelEventHandler(MyListView_Closing);
         this._parentForm.Load -= new EventHandler(MyListView_Load);
      }
   }

   private void MyListView_Load(object sender, EventArgs e)
   {
      MessageBox.Show("The parent form is loading!");
   }

   private void LastParent_ParentChanged(object sender, EventArgs e)
   {
      Control Source = (Control)sender;

      if (Source.TopLevelControl != null && Source.TopLevelControl is Form)
      {
         this._parentForm = (Form)Source.TopLevelControl;
         this.EstablishParentEvents();
      }
   }
}

from a solution provided by Neil Tonkin in Message #1084683