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

GIMP 2.8.14p2 - Powerful, free image edi...
GIMP is a multi-platform photo manipulation tool. GIMP is an acronym for GNU Image Manipulation Program. The GIMP is suitable for a variety of image manipulation tasks, including photo retouching,... Read more
Sandvox 2.10.2 - Easily build eye-catchi...
Sandvox is for Mac users who want to create a professional looking website quickly and easily. With Sandvox, you don't need to be a Web genius to build a stylish, feature-rich, standards-compliant... Read more
LibreOffice 5.0.1.2 - Free, open-source...
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
f.lux 36.1 - Adjusts the color of your d...
f.lux makes the color of your computer's display adapt to the time of day, warm at night and like sunlight during the day. Ever notice how people texting at night have that eerie blue glow? Or wake... Read more
VirtualBox 5.0.2 - x86 virtualization so...
VirtualBox is a family of powerful x86 virtualization products for enterprise as well as home use. Not only is VirtualBox an extremely feature rich, high performance product for enterprise customers... Read more
File Juicer 4.43 - Extract images, video...
File Juicer is a drag-and-drop can opener and data archaeologist. Its specialty is to find and extract images, video, audio, or text from files which are hard to open in other ways. In computer... Read more
Apple MainStage 3.2 - Live performance t...
MainStage 3 makes it easy to bring to the stage all the same instruments and effects that you love in your recording. Everything from the Sound Library and Smart Controls you're familiar with from... Read more
formZ 8.5 - Solid and surface modeler. (...
formZ pro is a powerful 3D design application featuring a variety of modeling personalities and tools with an easy to use interface to express and communicate your imagination. It is based on... Read more
PopChar 7.2 - Floating window shows avai...
We're also selling a 5-license family pack for only $25.99! PopChar helps you get the most out of your font collection. With its crystal-clear interface, PopChar provides a frustration-free way to... Read more
FileMaker Pro 14.0.2 - Powerful, easy-to...
FileMaker Pro is powerful, easy-to-use software used to create custom solutions for your business that run on iPad, iPhone, Windows, Mac and the web. Use FileMaker Pro to manage and share information... Read more

ReBoard: Revolutionary Keyboard (Utilit...
ReBoard: Revolutionary Keyboard 1.0 Device: iOS Universal Category: Utilities Price: $1.99, Version: 1.0 (iTunes) Description: Do everything within the keyboard without switching apps! If you are in WhatsApp, how do you schedule a... | Read more »
Tiny Empire (Games)
Tiny Empire 1.1.3 Device: iOS Universal Category: Games Price: $2.99, Version: 1.1.3 (iTunes) Description: Launch cannonballs and blow tiny orcs into thousands of pieces in this intuitive fantasy-themed puzzle shooter! Embark on an... | Read more »
Astropad Mini (Productivity)
Astropad Mini 1.0 Device: iOS iPhone Category: Productivity Price: $4.99, Version: 1.0 (iTunes) Description: *** 50% off introductory price! ​*** Get the high-end experience of a Wacom tablet at a fraction of the price with Astropad... | Read more »
Emo Chorus (Music)
Emo Chorus 1.0.0 Device: iOS Universal Category: Music Price: $1.99, Version: 1.0.0 (iTunes) Description: Realistic Choir simulator ranging from simple Chorus emulation to full ensemble Choir with 128 members. ### introductory offer... | Read more »
Forest Spirit (Games)
Forest Spirit 1.0.5 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0.5 (iTunes) Description: | Read more »
Ski Safari 2 (Games)
Ski Safari 2 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: The world's most fantastical, fun, family-friendly skiing game is back and better than ever! Play as Sven's sister Evana, share... | Read more »
Lara Croft GO (Games)
Lara Croft GO 1.0.47768 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0.47768 (iTunes) Description: Lara Croft GO is a turn based puzzle-adventure set in a long-forgotten world. Explore the ruins of an ancient... | Read more »
Whispering Willows (Games)
Whispering Willows 1.23 Device: iOS Universal Category: Games Price: $4.99, Version: 1.23 (iTunes) Description: **LAUNCH SALE 50% OFF** - Whispering Willows is on sale for 50% off ($4.99) until September 9th. | Read more »
Calvino Noir (Games)
Calvino Noir 1.1 Device: iOS iPhone Category: Games Price: $3.99, Version: 1.1 (iTunes) Description: The film noir stealth game. Calvino Noir is the exploratory, sneaking adventure through the 1930s European criminal underworld.... | Read more »
Angel Sword (Games)
Angel Sword 1.0 Device: iOS Universal Category: Games Price: $6.99, Version: 1.0 (iTunes) Description: Prepare to adventure in the most epic full scale multiplayer 3D RPG for mobile! Experience amazing detailed graphics in full HD.... | Read more »

Price Scanner via MacPrices.net

Tablet Screen Sizes Expanding as iPad Pro App...
Larger screen sizes are gaining favor as the tablet transforms into a productivity device, with shipments growing 185 percent year-over-year in 2015. According to a new Strategy Analytics’ Tablet... Read more
Today Only: Save US$50 on Adobe Elements 13;...
Keep the memories. lose the distractions. Summer’s winding down and it’s time to turn almost perfect shots into picture perfect memories with Elements 13. And get the power to edit both photos and... Read more
1.4GHz Mac mini on sale for $449, save $50
Best Buy has the 1.4GHz Mac mini on sale for $50 off MSRP on their online store. Choose free shipping or free local store pickup (if available). Price for online orders only, in-store price may vary... Read more
12-inch 1.1GHz Gold MacBook on sale for $1149...
B&H Photo has the 12″ 1.1GHz Gold Retina MacBook on sale for $1149.99 including free shipping plus NY sales tax only. Their price is $150 off MSRP, and it’s the lowest price available for this... Read more
27-inch 3.3GHz 5K iMac on sale for $1849, sav...
Best Buy has the 27″ 3.3GHz 5K iMac on sale for $1849.99. Their price is $150 off MSRP, and it’s the lowest price available for this model. Choose free shipping or free local store pickup (if... Read more
Worldwide Tablet Shipments Expected to Declin...
Does Apple badly need a touchscreen convertible/hybrid laptop MacBook? Yes, judging from a new market forecast from the International Data Corporation (IDC) Worldwide Quarterly Tablet Tracker, which... Read more
Continued PC Shipment Shrinkage Expected Thro...
Worldwide PC shipments are expected to fall by -8.7 percent in 2015 and not stabilize until 2017, according to the latest International Data Corporation (IDC) Worldwide Quarterly PC Tracker data. The... Read more
Imminent iPhone 6s Announcement Leads To 103%...
NextWorth Solutions, with its online and in-store electronics trade-in programs including http://NextWorth.com, reports that it has experienced a 103 percent surge in quoted trade-in values over the... Read more
Weekend Deal: 13-inch Retina MacBook Pros for...
Save up to $100 on the purchase of a new 2015 13″ Retina MacBook Pro at the following resellers this weekend. Shipping is free with each model: 2.7GHz/128GB MSRP $1299 2.7GHz/... Read more
13-inch 2.5GHz MacBook Pro on sale for $999,...
B&H Photo has the 13″ 2.5GHz MacBook Pro on sale for $999.99 including free shipping plus NY sales tax only. Their price is $100 off MSRP. Read more

Jobs Board

Senior Payments Security Manager - *Apple*...
**Job Summary** Apple , Inc. is looking for a highly motivated, innovative and hands-on senior payments security manager to join the Apple Pay security team. You will Read more
Software QA Engineer, *Apple* Pay Security...
**Job Summary** Imagine what you could do here. At Apple , great ideas have a way of becoming great products, services, and customer experiences very quickly. Bring Read more
Business Process Engineer ( *Apple* Online S...
**Job Summary** The Apple Online Support Planning team is looking for an experienced Business Process engineer to lead key business process improvement initiatives Read more
*Apple* Solutions Consultant - Retail Sales...
**Job Summary** As an Apple Solutions Consultant (ASC) you are the link between our customers and our products. Your role is to drive the Apple business in a retail Read more
Product Design Engineer - *Apple* Watch - A...
**Job Summary** Product Design Engineer Job Description As a member of Apple 's Watch product design team, you will help to create the next generation of the world's Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.