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
$102.23
Apple Inc.
+2.47
MSFT
$44.61
Microsoft Corpora
+0.53
GOOG
$520.91
Google Inc.
+0.07

MacTech Search:
Community Search:

Software Updates via MacUpdate

NTFS 12.0.39 - Provides full read and wr...
Paragon NTFS breaks down the barriers between Windows and OS X. Paragon NTFS effectively solves the communication problems between the Mac system and NTFS, providing full read and write access to... Read more
RestoreMeNot 2.0.3 - Disable window rest...
RestoreMeNot provides a simple way to disable the window restoration for individual applications so that you can fine-tune this behavior to suit your needs. Please note that RestoreMeNot is designed... Read more
Macgo Blu-ray Player 2.10.9.1750 - Blu-r...
Macgo Mac Blu-ray Player can bring you the most unforgettable Blu-ray experience on your Mac. Overview Macgo Mac Blu-ray Player can satisfy just about every need you could possibly have in a Blu-ray... Read more
Apple iOS 8.1 - The latest version of Ap...
The latest version of iOS can be downloaded through iTunes. Apple iOS 8 comes with big updates to apps you use every day, like Messages and Photos. A whole new way to share content with your family.... Read more
TechTool Pro 7.0.5 - Hard drive and syst...
TechTool Pro is now 7, and this is the most advanced version of the acclaimed Macintosh troubleshooting utility created in its 20-year history. Micromat has redeveloped TechTool Pro 7 to be fully 64... Read more
PDFKey Pro 4.0.2 - Edit and print passwo...
PDFKey Pro can unlock PDF documents protected for printing and copying when you've forgotten your password. It can now also protect your PDF files with a password to prevent unauthorized access and/... Read more
Yasu 2.9.1 - System maintenance app; per...
Yasu was originally created with System Administrators who service large groups of workstations in mind, Yasu (Yet Another System Utility) was made to do a specific group of maintenance tasks... Read more
Hazel 3.3 - Create rules for organizing...
Hazel is your personal housekeeper, organizing and cleaning folders based on rules you define. Hazel can also manage your trash and uninstall your applications. Organize your files using a... Read more
Autopano Giga 3.7 - Stitch multiple imag...
Autopano Giga allows you to stitch 2, 20, or 2,000 images. Version 3.0 integrates impressive new features that will definitely make you adopt Autopano Pro or Autopano Giga: Choose between 9... Read more
MenuMeters 1.8 - CPU, memory, disk, and...
MenuMeters is a set of CPU, memory, disk, and network monitoring tools for Mac OS X. Although there are numerous other programs which do the same thing, none had quite the feature set I was looking... Read more

Latest Forum Discussions

See All

Clips Review
Clips Review By Jennifer Allen on October 21st, 2014 Our Rating: :: CONVENIENT PASTINGUniversal App - Designed for iPhone and iPad Making copying and pasting more powerful than usual, Clips is a great way to move stuff around.   | Read more »
MonSense Review
MonSense Review By Jennifer Allen on October 21st, 2014 Our Rating: :: ORGANIZED FINANCESiPhone App - Designed for the iPhone, compatible with the iPad Organize your finances with the quick and easy to use, MonSense.   | Read more »
This Week at 148Apps: October 13-17, 201...
Expert App Reviewers   So little time and so very many apps. What’s a poor iPhone/iPad lover to do? Fortunately, 148Apps is here to give you the rundown on the latest and greatest releases. And we even have a tremendous back catalog of reviews; just... | Read more »
Angry Birds Transformers Review
Angry Birds Transformers Review By Jennifer Allen on October 20th, 2014 Our Rating: :: TRANSFORMED BIRDSUniversal App - Designed for iPhone and iPad Transformed in a way you wouldn’t expect, Angry Birds Transformers is a quite... | Read more »
GAMEVIL Announces the Upcoming Launch of...
GAMEVIL Announces the Upcoming Launch of Mark of the Dragon Posted by Jessica Fisher on October 20th, 2014 [ permalink ] Mark of the Dragon, by GAMEVIL, put | Read more »
Interview With the Angry Birds Transform...
Angry Birds Transformers recently transformed and rolled out worldwide. This run-and-gun title is a hit with young Transformers fans, but the ample references to classic Transformers fandom has also earned it a place in the hearts of long-time... | Read more »
Hail to the King: Deathbat Review
Hail to the King: Deathbat Review By Rob Thomas on October 20th, 2014 Our Rating: :: SO FAR AWAYUniversal App - Designed for iPhone and iPad Hail to the King: Deathbat may feel like “Coming Home” for Avenged Sevenfold’s faithful,... | Read more »
Find Free Food on Campus with Ypay
Find Free Food on Campus with Ypay Posted by Jessica Fisher on October 20th, 2014 [ permalink ] iPhone App - Designed for the iPhone, compatible with the iPad | Read more »
Strung Along Review
Strung Along Review By Jordan Minor on October 20th, 2014 Our Rating: :: GOT NO STRINGSUniversal App - Designed for iPhone and iPad A cool gimmick and a great art style keep Strung Along from completely falling apart.   | Read more »
P2P file transferring app Send Anywhere...
File sharing services like Dropbox have security issues. Email attachments can be problematic when it comes to sharing large files. USB dongles don’t fit into your phone. Send Anywhere, a peer-to-peer file transferring application, solves all of... | Read more »

Price Scanner via MacPrices.net

Strong iPhone, Mac And App Store Sales Drive...
Apple on Monday announced financial results for its fiscal 2014 fourth quarter ended September 27, 2014. The Company posted quarterly revenue of $42.1 billion and quarterly net profit of $8.5 billion... Read more
Apple Posts How-To For OS X Recovery
OS X 10.7 Lion and later include OS X Recovery. This feature includes all of the tools you need to reinstall OS X, repair your disk, and even restore from a Time Machine backup. OS X Recovery... Read more
Mac OS X Versions (Builds) Supported By Vario...
Apple Support has posted a handy resource explaining which Mac OS X versions (builds) originally shipped with or are available for your computer via retail discs, downloads, or Software Update. Apple... Read more
Deals on 2011 13-inch MacBook Airs, from $649
Daily Steals has the Mid-2011 13″ 1.7GHz i5 MacBook Air (4GB/128GB) available for $699 with a 90 day warranty. The Mid-2011 13″ 1.7GHz i5 MacBook Air (4GB/128GB SSD) is available for $649 at Other... Read more
2013 15-inch 2.0GHz Retina MacBook Pro availa...
B&H Photo has leftover previous-generation 15″ 2.0GHz Retina MacBook Pros now available for $1599 including free shipping plus NY sales tax only. Their price is $400 off original MSRP. B&H... Read more
Updated iPad Prices
We’ve updated our iPad Air Price Tracker and our iPad mini Price Tracker with the latest information on prices and availability from Apple and other resellers, including the new iPad Air 2 and the... Read more
Apple Pay Available to Millions of Visa Cardh...
Visa Inc. brings secure, convenient payments to iPad Air 2 and iPad mini 3as well as iPhone 6 and 6 Plus. Starting October 20th, eligible Visa cardholders in the U.S. will be able to use Apple Pay,... Read more
Textkraft Pocket – the missing TextEdit for i...
infovole GmbH has announced the release and immediate availability of Textkraft Pocket 1.0, a professional text editor and note taking app for Apple’s iPhone. In March 2014 rumors were all about... Read more
C Spire to offer iPad Air 2 and iPad mini 3,...
C Spire on Friday announced that it will offer iPad Air 2 and iPad mini 3, both with Wi-Fi + Cellular, on its 4G+ LTE network in the coming weeks. C Spire will offer the new iPads with a range of... Read more
Belkin Announces Full Line of Keyboards and C...
Belkin International has unveiled a new lineup of keyboard cases and accessories for Apple’s newest iPads, featuring three QODE keyboards and a collection of thin, lightweight folios for both the... Read more

Jobs Board

*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
Project Manager / Business Analyst, WW *Appl...
…a senior project manager / business analyst to work within our Worldwide Apple Fulfillment Operations and the Business Process Re-engineering team. This role will work 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
Position Opening at *Apple* - Apple (United...
…customers purchase our products, you're the one who helps them get more out of their new Apple technology. Your day in the Apple Store is filled with a range of Read more
Position Opening at *Apple* - Apple (United...
**Job Summary** At the Apple Store, you connect business professionals and entrepreneurs with the tools they need in order to put Apple solutions to work in their Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.