C#

private Boolean mouseDown = false;

....

splitContainer.MouseMove += SplitContainer_MouseMove;
splitContainer.MouseDown += SplitContainer_MouseDown;
splitContainer.MouseUp += SplitContainer_MouseUp;
splitContainer.SplitterMoving += SplitContainer_SplitterMoving;
....

private void SplitContainer_MouseDown(object sender, MouseEventArgs e) {
  mouseDown = true;
}

private void SplitContainer_MouseUp(object sender, MouseEventArgs e) {
  mouseDown = false;
}

private void SplitContainer_SplitterMoving(object sender, SplitterCancelEventArgs e) {
  // prevent default action
  e.Cancel = true;
}

private void SplitContainer_MouseMove(object sender, MouseEventArgs e) {
  SplitContainer sc = (SplitContainer)sender;
  if (mouseDown) {
    if (sc.Orientation == Orientation.Horizontal) {
      if (e.Y >= 0) {
        sc.SplitterDistance = e.Y;
      }
    } else {
      if (e.X >= 0) {
        sc.SplitterDistance = e.X;
      }
    }
  }
}

rtb2.Lines=new string[] { "line 1", "line 2", "line 3" };

richTextBox1.Lines = new string[2] { "", "111111" };

rtb2.Lines=new string[] { "line 1", "line 2", "line 3" };
string[] lines=rtb2.Lines;
lines[1]="new line 2";
rtb2.Lines=lines;

public class GameObject { ... }
public class Chest : GameObject {...}
public class TresureChest: GameObject {...}
...
public void PlayWithObject(GameObject go)
   {
   ...
   }

Chest ch = go as Chest;
if (ch != null)
   {
   ch.OpenChest();
   }

CsTreval wrote:

Is there any other way to do this other than casting it explicitly to a Chest type?

public class ABC
{
    public virtual string DoIt()
    {
        return "ABC";
    }
}

public class XYZ : ABC
{
    public override string DoIt()
    {
        return "XYZ";
    }
}

// Later on...
ABC a = new XYZ();
// str = "XYZ";
string str = a.DoIt();

Chest ch = new GameObject

Duck d = new Animal();
d.Quack(); // Not all animals know how to quack. You need a duck for that.
d = new Cat();
d.Quack(); // Cats can't quack.

public class GameObject
{
    public virtual void OpenGame() {...}
    public virtual void CloseGame() {...}
    //... and some more functions...
}