Sample Event Loop

/* Sample C Code of a Database Event Loop */

/* NOTE: The following code is not complete and provided for purposes of learning about the event loop. For experimentation, and as a typing aid, this portion of this file appears in

\SOURCE as DBEVENT.C */

/****************************************************************************

*************************************************************************

***************************************************************************

***************************************************************************/

/*****************************************************************************

******************************************************************************

*

* Global Data

*

/

EVENT app_event; /* System manager event struct */

LHAPIBLOCK CapData; /* LHAPI application data block */

/*----------------------------------------------------------------------

* far ptrs to be managed by sysmgr in event that memory moves. They must

* be registered with the sysmgr during initialization. The first

* MAX_CARD_WNDS are used to handle local titles for card windows, while the

* remainder are for database engine, note, multiline edit in general filter,

* and other miscellaneous uses that involve allocating memory block.

----------------------------------------------------------------------/

char far CardWndTitlePtrs[MAX_CARD_WNDS + 27]; / sysmgr farptrs */

/*----------------------------------------------------------------------

* Multitudinous other data declarations specific to your program would

* normally appear here, but are excluded from this example.

----------------------------------------------------------------------/

/* **

*

* Main entry point and event loop.

*

* Main contains init calls, event loop, error check, and uninit calls.

* This event loop is the ONLY one in the entire application.

* ** */

void main(int argc, char *argv[])

{

*/

Initialize();

/*-----------------------------------------------------------

* loop repeatedly for events until Done goes TRUE.

-----------------------------------------------------------/

eventloopstart:

while (!IndexBlock.Done) {

/*----------------------------------------------------------------------

* if there is stuff that could be lost from buffered disk i/o, send it

* on through before asking for keystroke.

----------------------------------------------------------------------/

if (Db.flags & DB_SHOULDFLUSH) { /* protect against warmstart */

if (DB_FlushFile(&Db) == DB_CLOSE)

SetError(ERR_WRITE);

}

/*----------------------------------------------------------------------

* Create error dlg if any errors reported during last event (or init).

* if db is closed and nofilewnd (DummyWnd) has not yet been launched,

* do it before creating error dlg. If no errors, cruise on by.

----------------------------------------------------------------------/

if (err = GetError()) { /* report errors if any */

SendMsg(&ErrorDlg,CREATE,CREATE_FOCUS,0);

}

/*----------------------------------------------------------------------

* Get an event (a keystroke or null(timer) event are the usuals.

----------------------------------------------------------------------/

maction:

app_event.do_event = DO_EVENT;

m_action (&app_event); /* Grab system manager event */

if (DB_CardChanged(&Db)<0)

goto restart;

switch (app_event.kind) { /* Branch on SysMgr event */

case E_KEY: /* users, the source of all troubles */

if (GetFocus())

SendFocusMsg(KEYSTROKE, app_event.data, app_event.scan);

else

goto restart;

break;

case E_REFRESH: /* redraw after sysmgr mucks up screen */

SendAllMsg(DRAW, DRAW_ALL, 0);

break;

case E_ACTIV: /* reactivate on rtn from other app */

HourglassOn(-1,-1);

if (DB_Reactivate(&Db) != DB_OK) { /* some file badness, restart app */

restart:

RestartApp(MyAppsHotKey);

m_fini(); /* but just in case, */

return; /* bail out cuz windows can't be operated */

}

ReactivateLHAPI(&CapData); /* things are OK, Hello LHAPI */

SyncLHAPIKeyState();

break;

case E_DEACT: /* switch to another app */

DB_Deactivate(&Db);

DeactivateLHAPI();

goto maction;

break;

case E_TERM: /* enforced bailout */

IndexBlock.Done = TRUE;

break;

case E_NONE:

SendMsg(GetFocus(), NULLEVENT, app_event.shifts, app_event.scan);

HandleClock(); /* show ticking clock (if enabled) */

break;

} /* end of switch on event type */

} /* end of event loop */

/*-----------------------------------------------------------

* Proof that miracles exist: no reboot this time.

-----------------------------------------------------------/

HourglassOn(-1,-1);

CloseDbFile(&Db); /* close current database */

m_fini(); /* Tell System Manager goodbye */

}

/* **

*

* Initialize CAP, SysMgr, Database, and data structures

*

/

void Initialize(void)

{

int i, size, err = 0;

char *titleptr;

char *bufptr;

char *pstuffptr;

/*----------------------------------------------------------------------

* Greet all the important local personalities

----------------------------------------------------------------------/

m_init_app(SYSTEM_MANAGER_VERSION); /* Hello SysMgr */

InitializeLHAPI(&CapData); /* Hello LHAPI */

/*----------------------------------------------------------------------

* setup far internal far pointers to be maintained by sysmgr. Initialize

* the first block for use by card window titles.

----------------------------------------------------------------------/

HourglassOn(-1,-1);

titleptr = CardWndTitles;

m_reg_far(&CardWndTitlePtrs, countof(CardWndTitlePtrs), 4);

for (i=0; i<MAX_CARD_WNDS; i++) {

CardWndTitlePtrs[i] = titleptr;

titleptr += DB_FIELDNAMELENGTH + 1;

CardWindow[i].Title = &CardWndTitlePtrs[i];

}

MultiBuffer = FilterBuffer;

EscBuffer = FileSpace;

LineStarts = Scratch2;

/*----------------------------------------------------------------------

* Set fonts, map in the resource file and init resource ptrs.

----------------------------------------------------------------------/

RegisterFont(FONT_NORMAL); /* be as normal as possible */

SetMenuFont(FONT_NORMAL);

SetDefaultFont(FONT_NORMAL);

map_resource_file("CDBAPP.RI"); /* map in resourced msgs */

Init_Db_Strings(); /* create access to those msgs */

/*-----------------------------------------------------------

* App specific initialization

*

* Must set EnvFileName, DfltDataFileName, ResourceFileName,

* DfltSmartClipName1/2, DfltCategory.

-----------------------------------------------------------/

InitAppPhone();

/*----------------------------------------------------------------------

* register the name of the application

* with the system manager for use in case low memory prompting is

* needed.

----------------------------------------------------------------------/

m_reg_app_name(IndexBlock.AppName); / register appname */

/*----------------------------------------------------------------------

* Init file dlgs, empty index window, and no-file window.

----------------------------------------------------------------------/

InitializeFileDialogs(); /* Hello File Dialogs */

BackupFileName = 0; / No 2nd chance if loadfile fails */

SendMsg(&TopWnd,CREATE,CREATE_FOCUS,0); /* Create main application window */

SendMsg(&DummyWnd, CREATE, CREATE_FOCUS, 0);

HourglassOn(-1,-1); /* put hourglass up again now that windows up */

/*----------------------------------------------------------------------

* Get name of current data file from environment file, use default file

* name if no environment file exists.

----------------------------------------------------------------------/

if (_dos_open(EnvFileName, O_RDWR, &EnvHandle))

lstrcpy(FileSpec, DfltDataFileName);

else {

_dos_lseek(EnvHandle, 0, SEEK_SET);

_dos_read(EnvHandle, FileSpec, sizeof(Db.filename), &size);

/*----------------------------------------------------------------------

* get printer setup information. dflts are already in place if read fails

----------------------------------------------------------------------/

i = sizeof(INDEXPRINTBLOCK);

bufptr = Record;

_dos_read(EnvHandle, bufptr, i, &size); /* read print setup info */

if (size == i) {

pstuffptr = (char *)&PStuff;

for (;i;i--) (pstuffptr++) = (bufptr++);

}

close:

_dos_close(EnvHandle);

}

/*----------------------------------------------------------------------

* init the db engine

----------------------------------------------------------------------/

err = DB_Init();

if (err || GetError()) {

SetError(ERR_DBINIT);

HourglassOff();

return;

}

/*----------------------------------------------------------------------

* if file is not default and does not exist, create no file state

* instead

----------------------------------------------------------------------/

if ((lstrcmp(FileSpec, DfltDataFileName)) && (!(Exists(FileSpec)))) {

SetError(ERR_OPEN);

HourglassOff();

return;

}

/*----------------------------------------------------------------------

* open up the datafile

----------------------------------------------------------------------/

LoadFileShell(NULL);

}

/* **

*

* Launches app; closes current app and launches again - last ditch

* recovery system when datafile deleted underneath.

*

/

int RestartApp(int HotKey)

{

struct task far *TCB = m_get_TCB();

int i;

for (i=0; i<TASKCOUNT; i++, TCB++)

if (HotKey==TCB->t_hotkey) goto launch;

return -1;

launch:

app_event.e_launch_task = i; /* Index of the app we want */

app_event.e_launch_type = LT_CLOSE_THEN_LAUNCH; /* Close us out first */

app_event.do_event = DO_LAUNCH;

m_action(&app_event); /* Launch our app */

return 1;

}