Solve the same window of MDI is repeated

DLL declares unique FRMCHILD: TFRMCHILD;

Call time

Call function of subform

IF not assigned (frmchild) THEN

FRMCHILD: = TfrmChild.create (Self);

Try

FRMCHILD.SHOW;

Finally

FRMCHILD.FREE;

FRMCHILD: = NIL;

END;

If you have created, you will not be created again, you can only show it out.