J2i.Net

Nothing at all and Everything in general.

Windows Mobile Current Directory

Another area when programming on Windows CE/Mobile devices is "How do I find the current directory?"  CE devices don't have a concept of a current directory.  This means that relative paths don't have meaning on a CE device (all paths are absolute).  Because of the lack or relative paths  some files (such as help files) are loaded to the Windows directory (personally I absolutly hate copying anything specific to an application to the Windows Directory).

It follows that since there is no concept of a current directory on a Windows Mobile device how would one locate a resource for which only a relative path is known?  A .Net program always has access to the modules of which it is composed (usually a .Net component is composed of one module packaged in a DLL or EXE file). The following line will return the absolute path to the currently executing assembly.

 string modulePath = this.GetType().Assembly.GetModules()[0].FullyQualifiedName;

 To get the absolute path to the folder that contains the assembly simple string manipulation is required.  The assembly name appears after the last directory seperator. While the directory seperator is usually the backslash (\) character, for better compatibility across other operating systems that may run .Net (ex: Mono[^] on Linux, OS X, or Solaris) use System.IO.Path.DirectorySeparator to represent the directory separator charactor.

string solutionFolder = modulePath.Substring(0, modulePath.LastIndexOf(Path.DirectorySeparatorChar) );

Once the folder to your program is known use Path.Combine to build the fully qualified file name for files in your folder.  Path.Combine takes into account the directory separator for the operating system on which your program is run.  So if you had data in a file named MyFile.txt you would use

string myFilePath = Path.Combine(solutionFolder,"MyFile.txt");

Update 1 : I received a simpler way to accomplish the same thing from John Spraul in the comment section.  Thanks. John!

Update 2: If you are developing using the native APIS use the following:
GetModuleFileName(GetModuleHandle(NULL),    pszFullPath, MAX_PATH);

Path.GetDirectoryName(this.GetType().Assembly.GetModules()[0].FullyQualifiedName)

or

Path.GetDirectoryName(Assembly.GetExecutingAssembly().GetModules()[0].FullyQualifiedName)

if you do not want to load the type.

WE-DIG Power Management

 WE-DIG (Windows Embeded Developer Interest Group) was looking at power management this past month and had a few tibits of information that I need to add to my power management FAQ.  You can read more about WE-DIG's finding at the Windows Embeded Blog.  They did some of their test using an AT&T Tilt (my current phone).  Changing the backlight settings on the Tilt had a huge difference on the devices battery life.  Depending on the settings the devices life ranged from 11 to 34 hours. They also mentioned that writing a file to a memory card uses 32 times the power of writing it to the built in memory.

A Month of Windows Mobile

This month Microsoft is providing 24 hours of webcast on Windows Mobile Development. The first webcast has already occurred, but the next one is in less than a week on how to use the Windows Mobile Emulator.  Having so many Windows Mobile devices one would think that I would have no need for the emulator, but this is far from the truth.  Developping without the emulator can potentially be expensive.  I'm developing some SMS based games at given that it cost $0.20 per message per device (which means $.40 for each message sent) debugging using real hardware starts to quickly have an impact on my pocket.

The following week there is a web cast on developing for different form factors.  I plan to register for that webcast too.  If you would like to register too here are the links to the registration page.

To Kill a Battery

I see this time and time again.  It's a practice that you don't want to do in a a mobile program or any other program for that matter. In multithread programming a deveoper will sometimes want to stop execution of a thread until a certain event occurs or some other task is complete and will write something like the following to halt execution.

while(taskNotDone)
{
   //Do nothing here
}

The problem with this code is it unnecessarily uses CPU bandwidth.  Most desktop applications spend a majorty of their time waiting on some event to occur (waiting on a user to press a key, waiting on a file to load, waiting on a network event to happen).  When the above code is used the CPU is burning cycles when it could have been halted waiting for something to occur or giving up those cycles to another more constructive task.  On a Windows Mobile device this type of coding pattern will lead to the CPU not going into a lower power state when it could and unnecessarily causes power to be asserted across the memory bus.

Instead of using the above pattern you could join threads (which will cause one thread to wait for another to finish executing) or use events, mutexes, and semaphores to block a thread until it is signaled by another thread to continue.  Within the course of the next few weeks I will cover some of these techniques.  In the mean time you may wish to read the article I published on Power Management.

My CE Devices

I had to pull out one of my older Pocket PCs for testing something and while I was at it I decided to round up my Windows CE devices and take a picture of them together.  I seem to have quite a bit.  Missing from the history of devices that I've owned are an i-mate Jam and the ViewSonic V37.  Regretably I sold one and gave the other to some one that wanted a PocketPC.  I hope to get a Windows Mobile 6 standard device and a Windows CE development kit in the coming months.

 

My Windows CD Devices

Power Management Article Published

I've taken the discussion of the power button and have expanded upon it in the form of an article on power management in Widnows Mobile devices.  I've published it at my favorite online dev community site, codeproject.com.  Go over to http://www.codeproject.com/script/Articles/Article.aspx?aid=28886 and take a look at the article.  If you find the information usefule then please log in and rate it!

What Does the Power Button Do?

The iIimpact of unobservable events has long been a subject over which humans have pondered.    Some questions are either well known or commonly shared.

  • If a tree falls in the forest and no one hears it then does it make a sound?
  • When I close the door on the fridge does the light go out?
  • Is Schrodinger's cat dead or alive?
  • When I press the power button on my Windows Mobile phone do the programs stop running?

These are all questions will all be answered by the end of this blog post. Thanks to the availability of inexpensive electronics such as digital video and audio recorders we can show that falling tress make noises and that the lights in the fridge do go out.  Figuring out what happens when the power button is pressed on Windows Mobile was a little more difficult.

My first attempt at answering this question was based on programs that changed what they were displaying  over their execute cycles.  If the Windows Mobile device suspends when I press the power button then after pressing the button, waiting a few seconds, and pressing it again the program's display should show the same thing that it did before I pressed the button.  If the device continues to run when I press the power button then after the test I should see something that is noticably different. I ran my test and concluded that the processor continued to run after the power button was pressed.  As it turned out my initial conclusion was wrong.

After performing much more research on the matter I found that my conclusion contradicticted other material I found such as the "Power to the Programmers" post on the Windows Mobile Team Blog. I performed my tests again and increased the amount of time that I left the device in its alleged suspended state.  After successive test I achieved enlightenment.   Pressing the power button on a Windows Mobile Professional device powers down the display and some other hardware, but the processor continues to run.  After a certain amount of time has passed unless a program has indicated a desire to do otherwise the device's processor will halt until something wakes it up.  When the device is in this state it's not off; the programs are still in memory.  Windows Mobile Standard devices are always on, there's no questioning that.

In a forthcoming post I'll cover the details of power control on Windows Mobile devices.

So the only question that leaves open is whether or not Schrodinger's cat is alive. I will leave that question unanswerd and hope for the best for his cat.

Windows Mobile 6.1 Upgrade for Tilt?

HTC's support site is in a state of flux for the AT&T Tilt (a version of the HTC TyTn II).  The page is fluctuating between having a description for the Windows Mobile 6.0 ROM and the Windows Mobile 6.1 ROM.  Regardless of which page is displayed the Windows Mobile 6.0 rom is always the target of the download link.  I sent a question to their support department about this and they say the firmware update will be available by the end of the month.  Happy Days are Coming.

MFC and Windows Mobile

One of the things that I love about Microsoft is that once you learn a Microsoft technology parts of it are transferable to other Microsoft Platforms. The .Net technologies are an excellent example of this. There's also DirectX (portions of which can be used on Windows Mobile devices) and MFC.

Another such technology is MFC (Microsoft Foundation Classes).  MFC is a library of C++ application framework library for creating Windows applications.  It is a native code library, so you have full access to the native API without the need of platform invoke declarations or redeclaring structures for making native calls.  But it also provides several high level classes for creating UI elements and responding to windows messages. I would say that MFC lives half way between .Net based programs and traditional native non-MFC applications. 

I am engaging in a project for which it will be easier to use native code.  The project is going to rely on some third party native code libraries with a massive amount structures.  For the first phase of this project I plan to use MFC so that I can make a prototype with the third party library.  Later on I will make an abstraction layer that gives simpler access to the functionality that I need and then I will create a .Net wrapper for it.  In the coming weeks once the project reaches a certain level of functionality, stability, and presentability I'll be posting the code on CodeProject.com.  I don't want to say anything about the nature of the project just yet, but I'm sure it will be very popular!