how to return object to parent window form

The way I generally handle this is to create a public object in the child form which will be accessible in the form object once the child form has hidden itself.  I.E.

// Mainline
ChildForm frm = new ChildForm();
MyObject obj;

frm.ShowDialog();
obj = frm.PublicObject;   // Establishing a local reference to the object in the form.

// ... in ChildForm

class ChildForm as System.Whatever.Form {
   public MyObject PublicObject = new MyObject();

   // Somewhere in form code assign the properties to the object ...

}

I don't know of a mechanism by which a form "returns" an object to the caller of ShowDialog() however presenting the object as a public property of the child form is always how I've been able to retrieve values from the child form while it still exists.

Just keep in mind that the form itself will still live in memory if you have a reference to the public object so you might want to copy the contents of the public object in the form to a newly instantiated version of your object instead so that assignment above doesn't have to be made directly to the object (which will keep the garbage collector from getting rid of the form).

HTH,

-bruce