mrNone 0 None. Used as a default value before the user exits.
mrOk 1 The user exited with OK button.
mrCancel 2 The user exited with the CANCEL button.
mrYes 3 The user exited with the YES button.
mrNo 4 The user exited with the NO button.
mrAbort 5 The user exited with the ABORT button.
mrRetry 6 The user exited with the RETRY button.
mrIgnore 7 The user exited with the IGNORE button.
mrAll 8 The user exited with the ALL button.
mrNoToAll 9 The user exited with the NO TO ALL button.
mrYesToAll 10 The user exited with the YES TO ALL button.
ModalResult是指一?模式窗体（form.showmodal）的返回值
原文：http://www.cnblogs.com/cm123/p/3992365.html