How deny to exit from CEdit

Question

I have subclassed CEdit clas (CMyEdit) and I am validating continuously user input througth ON_CHAR message. ON_CHAR procedure sets CMyEdit.isOK member variable to true or false. Is there any way how to deny exit from Edit Box, when the value is not rigth (.isOk = false)? I want not allow user to for example go to other edit box or to other dialog.

Thanks.