TweetFollow Us on Twitter

TicTacPalm 2

Volume Number: 19 (2003)
Issue Number: 1
Column Tag: Handheld Technologies

TicTacPalm 2

Saving Data in a Palm OS Application

by Danny Swarzman

Introduction

In a previous article ("TicTacPalm: Getting Started with Palm OS" in MacTech April, 2002), I presented a basic Palm OS application for a person to play Tic-Tac-Toe against the handheld computer. That article presented the structure of an application and the elements of the user interface. Here, we'll go one step further, adding the ability to save and restore documents.

On the Palm OS, each application can have one or more databases associated with it. Our sample application has only one database. Each record in the database is a game record. The user can review and modify saved games. This article shows how to save and restore game records. A future article will show how the game data can be transferred to a desktop computer.

The Application

TicTacPalm has three forms, a main game board form, a game list form, and game info form. The main form of the application is used both to enter new moves into a game and to review a game record. We use tape-recorder style buttons to review a game, moving forward or backwards. They are visible or hidden as needed. Figure 1 shows the board when reviewing a game.


Figure 1: The Game Board Form

The game list form has a scrolling list of names of games. The user selects a game to open or taps the New button to start a fresh game. (See Figure 2.) As you can see, there are buttons to open a game and to delete a game.


Figure 2: Game List Form

When the user deletes a game, the record doesn't completely disappear from the database. Instead, the record is marked for deletion. The record is eliminated when the next Hot Sync occurs. (We'll discuss this in greater detail in another article -- about conduits.)

In the game info form, the user enters the name that is to be associated with the game. The name doesn't need to be unique. The program distinguishes between games according to a record number.


Figure 3: Game Info Form

When the user taps OK in this form, control returns to the game board.

Figure 4 shows how the buttons can be used to navigate among the various forms. Menus could have been used instead of buttons. Menus require more effort to use, but they are needed when the application is more complex.


Figure 4: Links Among Forms

Databases

Creator and Type

A database on the Palm OS is a set of records associated with a creator and type. A creator is the 32-bit code corresponding to the application. An application can have several databases. The type is another 32-bit code that an application can use to distinguish among its databases.

Records

A record can be any size up to 64k bytes. Applications in which documents are larger must segment the documents. Palm OS does have a file system, which uses the Data Manager and is not particularly fast. Each record has flags that are maintained by the Data Manager and accessed through Data Manager functions.

  • The delete flag indicates that the user has deleted a record on the Palm OS device. When Hot Sync is performed, the file will be deleted on the desktop machine and finally be eliminated from the Palm OS device.

  • The dirty flag indicates that the record has been modified since the last Hot Sync.

  • The busy flag locks a record for writing.

  • The secret flag is cleared only when the user password has been entered.

Game Records

A program can open a record for reading. It can access it directly, as if it was just another chunk of memory. To write to a record, the application opens the record for writing. To do the actual writing, it calls a Data Manager routine to copy from another memory chunk to the record.

In this application, when a record is read, its data are copied into a CTicTacGame object. Data are written copying from a CTicTacGame object. When a game is opened, the board is displayed with the position as it was when the game was last closed.

CTicTacDatabase

This class handles the database access for the application. The declaration appears in Listing 1. It handles only one database.

Listing 1: Declaration of CTicTacDatabase

CTicTacDatabase
class   CTicTacDatabase
{
protected:
   class CTicTacGame *mGame;
   static DmOpenRef sOpenRef;
public:
      
   static Boolean Open();
   static void Close();
   static UInt16 Count();
   static void GetGame ( Int16 inRecordNumber,
            CTicTacGame *outGame);
   static void SetGame ( Int16 inRecordNumber,
            CTicTacGame *inGame);
   static Int16 Add ( CTicTacGame *inGame );
   static void Delete ( Int16 inRecordNumber );
   CTicTacDatabase ();
   virtual ~CTicTacDatabase ();
   
};

Listing 2 shows the functions to save and retrieve the current game.

Listing 2: Definition of ::GetGame and ::SetGame

CTicTacDatabase

void CTicTacDatabase :: GetGame ( Int16 inRecordNumber,
            CTicTacGame *outGame )
{
   // Open the database
   if ( Open() )
   {
      // Get the numbered record and lock it
      MemHandle dataHandle = DmGetRecord ( sOpenRef, 
            inRecordNumber );
      MemPtr dataPointer = MemHandleLock ( dataHandle );
      
      // Copy the data
      MemMove ( (void*)outGame, dataPointer, sizeof ( CTicTacGame ) );
      
      // Unlock release the record
      MemHandleUnlock ( dataHandle );
      DmReleaseRecord ( sOpenRef, inRecordNumber, false );
      // Close the database
      Close();
   }
   else
      outGame->Clear();
}
void CTicTacDatabase :: SetGame ( Int16 inRecordNumber,
   CTicTacGame *inGame )
{
   // Open the database
   if ( Open() )
   {
      // Get the numbered record and lock it
      MemHandle dataHandle = DmGetRecord ( sOpenRef, inRecordNumber );
      MemPtr dataPointer = MemHandleLock ( dataHandle );
      // Copy the data
      DmWrite ( dataPointer, 0, inGame, sizeof ( CTicTacGame ) );
      // Unlock release the record
      MemHandleUnlock ( dataHandle );
      DmReleaseRecord ( sOpenRef, inRecordNumber, true );
      Close();
   }
}

Preferences

The word preferences is a little misleading. This means that the data that is used to store information that the application needs to restore its state. Each time the user switches to a new application, the newly opened application needs to start where it left off the last time the user switched out of it.

For example, suppose the user switches out of the application while the Game Info form is displayed. The user may have been in the process of entering a new name. This partially entered new game name needs to reappear when the application is opened again. The case is similar for a selection made in the scrolling list in the Game List form. Let's see how this occurs.

CTicTacPreferences

The state of the current game is preserved in the application database when the application is switched out. This includes the state of the game. Listing 3 shows the declaration for the application task to deal with preferences.

Listing 3: Declaration of CTicTacPreferences

CTicTacPreferences
class   CTicTacPreferences 
{
protected:
   static CTicTacPreferences *sPreferences;
   struct PreferencesRecord
   {
      Int16 mCurrentRecord;
      Int16 mSelectedRecord;
      Int16 mLastFormID;
      GameNameType mUnconfirmedName;
   };
   PreferencesRecord mPreferencesRecord;
public:
   CTicTacPreferences();
   ~CTicTacPreferences();
   static Int16 GetCurrentRecord();
   static void SetCurrentRecord ( Int16 inRecord );
   static Int16 GetSelectedRecord();
   static void SetSelectedRecord ( Int16 inRecord );
   static Int16 GetLastForm();
   static void SetLastForm ( Int16 inFormID );
   static void GetUnconfirmedName ( GameNameType outGame );
   static void SetUnconfirmedName ( GameNameType inGame );   
};

Sequence of Events

When the user activates another application, the system sends an appStopEvent to the current application. The main event loop picks up the event and exits. Control goes back to TicTacPalmMain, which calls AppStop. AppStop closes the active forms. As each form is closed, a frmCloseEvent is sent to it.

AppStop is defined in Listing 4. The function first closes all forms and deletes the CTicTacPreferences object. Then it deletes the objects that handle user action. As each form is deleted, a frmCloseEvent is generated. The handler for the form saves the current state of the form in the preferences data. Then, when AppStop deletes the preferences, the preference data are written to disk.

Listing 4: Definition of AppStop

AppStop
static void AppStop(void)
{
   // Make sure the fields in each form are saved.
   FrmCloseAllForms ();
   
   if ( fPreferences )
   {
      delete fPreferences;
   }
   
   // Destroy the wrapper objects for forms.
   if ( fGameBoardForm )
   {
      delete fGameBoardForm;
      fGameBoardForm = NULL;
   }
   if ( fGameInfoForm )
   {
      delete fGameInfoForm;
      fGameInfoForm = NULL;
   }
   if ( fGameListForm )
   {
      delete fGameListForm;
      fGameListForm = NULL;
   }
}

CGameInfoForm::Close

When the system executes FrmCloseAllForms, the system sends a close event to each form. This event will be processed by the Close function for the Game Info form. That function, shown in Listing 5, saves the partially entered game name in the preferences.

Listing 5: Definition of ::Close

CGameInfoForm::Close
Boolean CGameInfoForm :: Close()
{
   GameNameType name;
   GetFieldText ( GameInfoNameFieldField, name );
   CTicTacPreferences :: SetUnconfirmedName ( name );
   // Return false to tell the OS to clean up the form
   // in the usual way after we have extracted the info.
   return false;
}

CTicTacPreferences Destructor

When the data in the CTicTacPreferences object are up-to-date, AppStop calls the destructor for the preferences object, which then stores its data, as shown in Listing 6.

Listing 5: Destructor for CTicTacPreferences

CTicTacPreferences::~CTicTacPreferences
CTicTacPreferences ::   ~CTicTacPreferences( )
{
   Boolean saved = true; // To be backed up at HotSync
   void *data = (void*)&mPreferencesRecord;
   UInt16 dataSize = sizeof ( PreferencesRecord );
   PrefSetAppPreferences (appFileCreator, appPrefID, 
            appPrefVersionNum, data, dataSize, saved );
   sPreferences = NULL;
}

Conclusion

Storing application data is relatively easy on the Palm OS, as long as the data takes less than 64k. Restoring the state of the application using Preferences data requires some thought. Both would be easier if there were an application framework to handle the messy details.

References and Credits

The Palm web site contains tons of information and links to related sites: http://www.palmos.com/dev/.

Thanks to Victoria Leonard for graphic resources. Thanks to Bob Ackerman, Mark Terry and Victoria Leonard for reviewing the text.


Danny Swarzman writes programs in JavaScript, Java, C++, and other languages. He also plays Go and grows potatoes. You can contact him with comments and job offers at dannys@stowlake.com, or you can visit his web site at http://www.stowlake.com.

 
AAPL
$112.51
Apple Inc.
+0.73
MSFT
$47.89
Microsoft Corpora
+0.23
GOOG
$523.23
Google Inc.
+6.88

MacTech Search:
Community Search:

Software Updates via MacUpdate

NeoOffice 2014.6 - Mac-tailored, OpenOff...
NeoOffice is a complete office suite for OS X. With NeoOffice, users can view, edit, and save OpenOffice documents, PDF files, and most Microsoft Word, Excel, and PowerPoint documents. NeoOffice 3.x... Read more
LibreOffice 4.3.5.2 - Free Open Source o...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
CleanApp 5.0.0 Beta 5 - Application dein...
CleanApp is an application deinstaller and archiver.... Your hard drive gets fuller day by day, but do you know why? CleanApp 5 provides you with insights how to reclaim disk space. There are... Read more
Monolingual 1.6.2 - Remove unwanted OS X...
Monolingual is a program for removing unnecesary language resources from OS X, in order to reclaim several hundred megabytes of disk space. It requires a 64-bit capable Intel-based Mac and at least... Read more
NetShade 6.1 - Browse privately using an...
NetShade is an Internet security tool that conceals your IP address on the web. NetShade routes your Web connection through either a public anonymous proxy server, or one of NetShade's own dedicated... Read more
calibre 2.13 - Complete e-library manage...
Calibre is a complete e-book library manager. Organize your collection, convert your books to multiple formats, and sync with all of your devices. Let Calibre be your multi-tasking digital librarian... Read more
Mellel 3.3.7 - Powerful word processor w...
Mellel is the leading word processor for OS X and has been widely considered the industry standard since its inception. Mellel focuses on writers and scholars for technical writing and multilingual... Read more
ScreenFlow 5.0.1 - Create screen recordi...
Save 10% with the exclusive MacUpdate coupon code: AFMacUpdate10 Buy now! ScreenFlow is powerful, easy-to-use screencasting software for the Mac. With ScreenFlow you can record the contents of your... Read more
Simon 4.0 - Monitor changes and crashes...
Simon monitors websites and alerts you of crashes and changes. Select pages to monitor, choose your alert options, and customize your settings. Simon does the rest. Keep a watchful eye on your... Read more
BBEdit 11.0.2 - Powerful text and HTML e...
BBEdit is the leading professional HTML and text editor for the Mac. Specifically crafted in response to the needs of Web authors and software developers, this award-winning product provides a... Read more

Latest Forum Discussions

See All

DICETINY is coming to iOS in 2015
DICETINY is coming to iOS in 2015 Posted by Jessica Fisher on December 22nd, 2014 [ permalink ] Fakedice has announced that they’re bringing their digital board game DICETINY to iOS. | Read more »
Living Room 3D for IKEA Makes All In-App...
Living Room 3D for IKEA Makes All In-App Purchases Free Until 2015 Posted by Jessica Fisher on December 22nd, 2014 [ permalink ] | Read more »
Crossbow Warrior – The Legend of William...
Crossbow Warrior – The Legend of William Tell Review By Lee Hamlet on December 22nd, 2014 Our Rating: :: MISSES THE MARKUniversal App - Designed for iPhone and iPad Crossbow Warrior details the entertaining adventures of legendary... | Read more »
Workflow: Powerful Automation Made Simpl...
Workflow: Powerful Automation Made Simple Review By Campbell Bird on December 22nd, 2014 Our Rating: :: GO WITH THE FLOWUniversal App - Designed for iPhone and iPad This powerful app lets users accomplish multiple tasks at touch of... | Read more »
My Little Monster Review
My Little Monster Review By Jordan Minor on December 22nd, 2014 Our Rating: :: IT'S ALIVE!Universal App - Designed for iPhone and iPad What’s it worth to make your own monster?   | Read more »
Galaxy Trucker Pocket (Games)
Galaxy Trucker Pocket 1.0.8 Device: iOS iPhone Category: Games Price: $2.99, Version: 1.0.8 (iTunes) Description: Galaxy Truckers Wanted!================================================================= (5/5) "Galaxy Trucker isn’t... | Read more »
Make your own Tribez Figures (and More)...
Make your own Tribez Figures (and More) with Toyze Posted by Jessica Fisher on December 19th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
So Many Holiday iOS Sales Oh My Goodness...
The holiday season is in full-swing, which means a whole lot of iOS apps and games are going on sale. A bunch already have, in fact. Naturally this means we’re putting together a hand-picked list of the best discounts and sales we can find in order... | Read more »
It’s Bird vs. Bird in the New PvP Mode f...
It’s Bird vs. Bird in the New PvP Mode for Angry Birds Epic Posted by Jessica Fisher on December 19th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Telltale Games and Mojang Announce Minec...
Telltale Games and Mojang Announce Minecraft: Story Mode – A Telltale Games Series Posted by Jessica Fisher on December 19th, 2014 [ permalink ] | Read more »

Price Scanner via MacPrices.net

13-inch 2.4GHz Retina MacBook Pro (Apple refu...
The Apple Store has previous-generation Apple Certified Refurbished 13″ 2.4GHz/128GB Retina MacBook Pros available for $999. Apple’s one-year warranty is standard, and shipping is free: - 13″ 2.4GHz/... Read more
Apple resellers offer free overnight shipping
The Apple Store is now offering free next-day shipping on all in stock items if ordered before 12/23/14 at 10:00am PT. Local store pickup is also available within an hour of ordering for any in stock... Read more
Holiday sales continue: MacBook Airs for up t...
 B&H Photo has 2014 MacBook Airs on sale for up to $120 off MSRP, for a limited time, for the Thanksgiving/Christmas Holiday shopping season. Shipping is free, and B&H charges NY sales tax... Read more
Holiday sale continues: 13-inch Retina MacBoo...
 B&H Photo has new 13″ MacBook Pros on sale for up to $150 off MSRP as part of their Holiday pricing. Shipping is free, and B&H charges NY sales tax only: - 13″ 2.5GHz MacBook Pro: $979 save... Read more
Holiday sale continues: 15-inch Retina MacBoo...
 B&H Photo has the new 2014 15″ Retina MacBook Pros on sale for up to $300 off MSRP for a limited time. Shipping is free, and B&H charges NY sales tax only: - 15″ 2.2GHz Retina MacBook Pro: $... Read more
Holiday sale: 13-inch 128GB MacBook Air for $...
 Best Buy has the 2014 13-inch 1.4GHz 128GB MacBook Air on sale for $849.99, or $150 off MSRP, on their online store. Choose free home shipping or free local store pickup (if available). Price valid... Read more
13-inch 2.6GHz Retina MacBook Pro on sale for...
Best Buy has lowered their price on the 2014 13″ 2.6GHz/128GB Retina MacBook Pro to $1149.99 on their online store for a limited time. That’s $150 off MSRP and the lowest price available for this... Read more
Kodak Returns to CES With New Consumer Produ...
Former photography colossus Kodak is returning to CES for the first time in three years where the Kodak booth (#21818 South Hall 1) will showcase a wide range of innovative, imaging-related products... Read more
Invaluable Launches New Eponymously -Named A...
Invaluable, the world’s largest online live auction marketplace, hhas announced the official launch of the Invaluable app for iPad, now available for download in the iTunes App Store. Invaluable... Read more
IDC Reveals Worldwide Mobile Enterprise Appli...
International Data Corporation (IDC) last week hosted the IDC FutureScape: Worldwide Mobile Enterprise Applications and Solutions 2015 Predictions Web conference. The session provided organizations... Read more

Jobs Board

*Apple* Store Leader Program (US) - Apple, I...
…Summary Learn and grow as you explore the art of leadership at the Apple Store. You'll master our retail business inside and out through training, hands-on experience, Read more
Project Manager, *Apple* Financial Services...
**Job Summary** Apple Financial Services (AFS) offers consumers, businesses and educational institutions ways to finance Apple purchases. We work with national and Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.