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.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

NTFS 14.3.318 - $19.95
This latest version supports the new macOS 10.12 Sierra! NTFS breaks down the barriers between Windows and OS X. Paragon NTFS effectively solves the communication problems between the Mac system and... Read more
iFFmpeg 6.2.2 - Convert multimedia files...
iFFmpeg is a comprehensive media tool to convert movie, audio and media files between formats. The FFmpeg command line instructions can be very hard to master/understand, so iFFmpeg does all the hard... Read more
ForeverSave 2.1.6 - Universal auto-save...
ForeverSave auto-saves all documents you're working on while simultaneously doing backup versioning in the background. Lost data can be quickly restored at any time. Define your preferred time... Read more
BetterTouchTool 1.961 - Customize Multi-...
BetterTouchTool adds many new, fully customizable gestures to the Magic Mouse, Multi-Touch MacBook trackpad, and Magic Trackpad. These gestures are customizable: Magic Mouse: Pinch in / out (zoom... Read more
EtreCheck 3.1.4 - For troubleshooting yo...
EtreCheck is an app that displays the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to... Read more
Together 3.7 - Store and organize all of...
Together helps you organize your Mac, giving you the ability to store, edit and preview your files in a single clean, uncluttered interface. Features Smart storage. With simple drag-and-drop... Read more
Together 3.7 - Store and organize all of...
Together helps you organize your Mac, giving you the ability to store, edit and preview your files in a single clean, uncluttered interface. Features Smart storage. With simple drag-and-drop... Read more
EtreCheck 3.1.4 - For troubleshooting yo...
EtreCheck is an app that displays the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to... Read more
Postbox 5.0.9 - Powerful and flexible em...
Postbox is a new email application that helps you organize your work life and get stuff done. It has all the elegance and simplicity of Apple Mail, but with more power and flexibility to manage even... Read more
DiskCatalogMaker 6.5.16 - Catalog your d...
DiskCatalogMaker is a simple disk management tool which catalogs disks. Simple, light-weight, and fast. Finder-like intuitive look and feel. Super-fast search algorithm. Can compress catalog data... Read more

Latest Forum Discussions

See All

Silent Depth Submarine Simulation (Game...
Silent Depth Submarine Simulation 1.0 Device: iOS Universal Category: Games Price: $7.99, Version: 1.0 (iTunes) Description: | Read more »
Enneas Saga lets you lead your own demon...
Defend the land of Enneas Continent from the forces of evil in the new fantasy MMORPG from Lyto Mobi: Enneas Saga. Can’t wait? No problem. It’s available to download now on Android devices. | Read more »
Great zombie games in the spirit of Dead...
Dead Rising 4 arrives tomorrow, giving enthusiasts a fresh chance to take selfies with zombies and get up to other ridiculous end-of-the-world shenanigans. To really get into the spirit of things, we've gone and gathered the best zombie games that... | Read more »
Amateur Surgeon 4 Guide: Advanced tips a...
Amateur Surgeon 4 is still tackling the competition at the top of the App Store charts, so if you haven't tried it out yet, you should probably do that right away. If you've been at it for a while, though, perhaps you're ready to start expanding... | Read more »
Amateur Surgeon 4 Guide: Become the worl...
It's time to wield your trusty pizza cutter again, as Amateur Surgeon has returned with a whole fresh set of challenges (and some old, familiar ones, too). Starting anew isn't easy, especially when all you have at your disposal is a lighter, the... | Read more »
Le Parker: Sous Chef Extraordinaire (Ga...
Le Parker: Sous Chef Extraordinaire 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: | Read more »
Telltale Games really is working on a Gu...
Telltale Games' next episodic adventure is indeed Guardians of the Galaxy. A document tied to the voice actors strike suggested that the project was in the work, but now we have direct confirmation following an announcement at the Game Awards that... | Read more »
Amateur Surgeon returns to iOS and Andro...
Amateur Surgeon and its two sequels disappeared from the App Store some time and it was sad days for all. But now, just in time for the holidays, the Adult Swim favorite makes its joyous return in the shape of Amateur Surgeon 4, a remake with... | Read more »
The best board games on mobile
Sometimes you need to ditch all of the high speed, high action games in favor of something a little more traditional. If you don't feel like parting ways from your mobile device, though, there are still plenty of ways to get that old-school fix.... | Read more »
The best Facebook Messenger Instant Game...
Facebook's new Instant Games is now here, meaning you can play games with your friends directly via Facebook. It's a fun new way to connect with friends, of course, but it's also proving to be a solid gaming experience in its own right, with a... | Read more »

Price Scanner via MacPrices.net

Slate Tablet Market Share to Fall Below 75% i...
After two years of decline, the tablet market is showing signs of new life as productivity trumps entertainment, and tablets become cost-effective computing devices for both entertainment and... Read more
Yostand Launches Indigogo campaign for iStand...
China-based startup Yostand (meaning ‘your stand’), has announced the launch of its Indigogo campaign for their newly awaited iStand7. This product is a one of a kind iPhone battery case that offers... Read more
Green App – Budget Forecasting Now Available...
Indianapolis, Indiana based CoopToons has announced the release of Green – Budget Forecasting 1.5, an update to their personal budgeting app developed exclusively for iOS devices. Green aims to be a... Read more
New 2016 13-inch 2.0GHz MacBook Pros in stock...
Overstock.com has the non-Touch Bar 13″ MacBook Pros in stock today for $150 off MSRP. Shipping is free: - 13″ 2.0GHz MacBook Pro Space Gray (MLL42LL/A): $1349.99 $150 off MSRP - 13″ 2.0GHz MacBook... Read more
15-inch 2.6GHz Silver Touch Bar MacBook Pro o...
Adorama has the new 2016 15″ 2.6GHz Silver Touch Bar MacBook Pro (MLW72LL/A) in stock and available for $2349 including free shipping. Adorama charges sales tax in NY & NJ only. Their price is $... Read more
13-inch MacBook Airs on sale for up to $180 o...
Overstock.com has 13″ MacBook Airs on sale for up to $180 off MSRP including free shipping: - 13″ 1.6GHz/128GB MacBook Air (MMGF2LL/A): $869.99 $130 off MSRP - 13″ 1.6GHz/256GB MacBook Air (sku... Read more
13-inch 2.5GHz MacBook Pro (Apple refurbished...
Apple has Certified Refurbished 13″ 2.5GHz MacBook Pros (MD101LL/A) available for $829, or $270 off original MSRP. Apple’s one-year warranty is standard, and shipping is free: - 13″ 2.5GHz MacBook... Read more
Monday roundup of Holiday Mac sales: Up to $3...
Take up to $300 off MSRP on the price of a new Apple Mac at B&H Photo today as part of their Holiday sale. Shipping is free, and B&H charges NY sales tax only. Touch Bar MacBook Pros are in... Read more
12-inch WiFi Apple iPad Pros on sale for up t...
B&H Photo has 12″ WiFi Apple iPad Pros on sale for up to $50 off MSRP, each including free shipping. B&H charges sales tax in NY only: - 12″ Space Gray 32GB WiFi iPad Pro: $749 $50 off MSRP... Read more
9-inch Apple WiFi iPad Pros on sale for $20-$...
B&H Photo has 9.7″ Apple WiFi iPad Pros on sale for $20-$50 off MSRP, each including free shipping. B&H charges sales tax in NY only: - 9″ Space Gray 256GB WiFi iPad Pro: $779.95 $20 off MSRP... Read more

Jobs Board

*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Lead *Apple* Solutions Consultant - Apple (...
# Lead Apple Solutions Consultant Job Number: 53586123 Pittsburgh, Pennsylvania, United States Posted: Nov. 28, 2016 Weekly Hours: 40.00 **Job Summary** The Lead ASC Read more
*Apple* Retail - Multiple Positions- Plano,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Retail - Multiple Positions- Kansas...
Job Description:SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Retail - Multiple Positions- Chicago...
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.