All DatabasesMacTech Vol 07-1991
Password
Volume Number: 7
Issue Number: 7
Column Tag: C Workshop
Related Info: Dialog Manager
Password Dialogs
By Bill Schilit, New York, NY
Note: Source code files accompanying article are located on MacTech CD-ROM or
source code disks.
Making a Password Dialog
Bill Schilit has been programming the Macintosh since the days of the 128K. He
co-authored Macintosh Kermit, and the CAP Appletalk-Unix File Server. Bill is
currently a graduate student at Columbia University’s Computer Science department.
This article describes how to program a dialog with a non-displaying
“password” field. In this type of dialog, when the user types in his or her password all
they see are bullet characters (“•”) -- because you never know who may be looking
over your shoulder.
The password field of the dialog must handle delete, backspace, and replacement
of the text selection. Basically, even though you can’t see the characters being entered
you want it to act like a normal Text Edit field. One nice solution to the problem is to
create an offscreen TE field to hold the plain text password while the dialog TE field
holds the bullets.
The Login Dialog
In the program below, LoginDialog() is called to display the dialog box, it
returns the user name and password entered by the user. The filter procedure,
LoginFilter() does the real work here: it checks the name and password lengths, keeps
the offscreen TE record up to date, and exchanges the password character with a bullet.
LoginDialog() first loads the dialog from the resource file and then calls
SetPort() to set the GrafPort to the dialog window. SetPort is required for TENew() a
few lines below, since TextEdit remembers the GrafPort for you. The destination and
view rectangles we supply to TENew() are outside of the dialog window, so we never
actually see this TE field. After creating the invisible text edit field, a pointer to it is
stored in the dialog window via SetWRefCon() so that the filter procedure has access to
it.
The rest of LoginDialog() is fairly standard. The procedure loops until the user
types the OK button at which point the user name and password fields are copied for the
caller. Within the dialog loop the OK button is enabled or disabled -- if the password
and username have some type in then OK is enabled, otherwise it is disabled.
Figure 1. Password Dialog Box
The Login Filter
LoginFilter() is the standard filter procedure called by our modal dialog. If you
remember your Inside Mac then you know that returning TRUE from the filter proc
means we have handled the event, and the item number is in itemHit. Returning FALSE
lets ModalDialog process the event. Our filter proc is only concerned with keyboard
events, so the first line in procedure LoginFilter causes a return on all other types of
events.
The next task in LoginFilter() is to handle the characters tab and return (tab
moves to the next field and return is the same as the default button). The filter returns
here if either of these characters was typed.
The filter procedure now does the work of checking field lengths and setting those
bullets. The dialog’s text edit handle and the editField tell us which field is getting type
in and how large the current edit record is. We first check that adding the character
will not push us past the password or user name size limit, if so the filter gives a beep
and ignores the character. Notice that the auxiliary routine we call to check the length
of the text edit field given the new character is smart about checking for deletes,
backspace, and selection replacements.
When the character is destined for the password item we do our final
manipulations. The handle to our invisible text edit record is fetched from the dialog
refCon, and the selection (and insertion point) are set to be exactly the same as in the
password field. TEKey() is called to insert the character into our invisible text edit.
Now, unless the character is a delete or backspace, the character in the event record is
replaced by a bullet. We return to ModalDialog telling it to handle the event with the
now obscured character for the password field. When the dialog is complete, the
password is available from the invisible text edit field.
LOGIN DIALOG.C
/*
* Login Dialog.c - Dialog for User Login.
*
* Copyright (c) 1988 by Bill Schilit.
*
* Edit History:
*
* April 23, 1988 Schilit Created
* May 9, 1988 Schilit Clean up
*
*/
/* Includes MacHeaders */
#include "Login Dialog.h
/* Prototypes */
static int
TELengthCheck(TEPtr te,char c,int maxLen);
static void
TECpyText(TEHandle teH,Ptr p);
pascal Byte
LoginFilter(DialogPtr dPtr,
EventRecord *ePtr,short *iHit);
/*
* LDialogStg contains the global vars used
* by the filter proc and user item procs in
* our login dialog. A pointer to the
* LDialogStg is stored in the window refcon
* of the dialog window.
*/
typedef struct {
TEHandle passTeH;
} LDialogStg, *LDialogStgPtr;
/*
* static Byte
* LoginFilter(DialogPtr theDialog,
* EventRecord *theEvent,
* int *itemHit);
*
* Modal dialog filter to echo bullet
* ('\245') instead of the user's password
* and to limit the number of characters in
* both the user name and password edit
* records.
*/
static pascal Byte
LoginFilter(theDialog,theEvent,itemHit)
DialogPtr theDialog;
EventRecord *theEvent;
short *itemHit;
{
register char c;
int field,tooBig;
TEPtr tePtr;
LDialogStg *ldStg;
/* we're only interested in keyboard
* events. If not a key, let modal
* process as usual
*/
if (theEvent->what != keyDown &&
theEvent->what != autoKey)
return(false);
/* fetch the character from the
* event message
*/
c = theEvent->message & charCodeMask;
/* Check for CR and convert to OK button.
* Check for TAB and let it pass.
*/
if (c == CR) {
*itemHit = OK;
return(true);
}
if (c == '\t')
return(false);
/* make sure the edit text item is one
* we are interested in and check to see
* if the length is not too large.
*/
field =
((DialogPeek) theDialog)->editField+1;
tePtr =
*(((DialogPeek) theDialog)->textH);
/* User is typing in the nameItem --
* our only interest is the size
*/
if (field == nameItem) {
tooBig =
TELengthCheck(tePtr,c,MAXNAME);
/* give a beep if too big, and return
* TRUE to ignore the event.
*/
if (tooBig)
SysBeep(1);
return(tooBig);
}
/* If typing into the password, check the
* size, then diddle the character so
* bullet (\245) shows up instead of what
* the user typed.
*/
if (field == passwdItem) {
if (TELengthCheck(tePtr,c,MAXPWD)) {
SysBeep(1);
return(true);
}
/* Insert the char into our private
* password text edit record. First
* set the text selection so action
* mimicks exactly what user is
* selecting and typing in passwdItem
* text edit field.
*/
ldStg = (LDialogStg *)
GetWRefCon(theDialog);
if (ldStg == 0)
return(false);
TESetSelect(tePtr->selStart,
tePtr->selEnd,
ldStg->passTeH);
TEKey(c,ldStg->passTeH);
/* unless BS or DEL, replace the
* password character with bullet
*/
if (c != DEL && c != BS)
theEvent->message = '\245' |
(theEvent->message &
~charCodeMask);
return(false); /* return ok */
}
return(false); /* all other items */
}
/*
* static int
* TELengthCheck(tePtr te,char c,int maxLen)
*
* Check that adding character c to the text
* edit te does not cause more than maxLen
* chars in the text edit item:
*
* 1) If delete or backspace then length will
* decrease so ok.
* 2) If a selection range of 1 or more chars
* then same as above.
* 3) Finally just check the length of the
* edit item.
*
*
* Returns: FALSE if OK, TRUE if too large.
*
*/
static int
TELengthCheck(te,c,maxLen)
Referenced by (11):