Aleksandr Trufanov's Blog

Yeah, that's not a mistake. I've just faced with one special (probably rare) case where the installation time of Symbian QML application had been reduced from 8 min to 30 sec.

How much time do you think could take an installation of 15Mb symbian sis package file without SmartInstaller wrapping? A minute, two? Actually, the right answer depends mostly not on the sis file size but on the number of files in sis package. In general, sis package is just a zip archive with installation script inside. Script execution and file I/O operations took most of the time. In my case I had a QML application with a bit more than 500 image files inside. And it tooks 8 min for my N8-00 to install it on embedded memory card and 3,5 to uninstall. Yeah, there might be applications that require so many graphic files, for example ebooks and card-learning systems as well as games.

To make sure the problem is not sis size dependent I replaced all image files (~19Mb) with only 2 files 10Mb each. And installation proceeds 10 times faster.

So, could we put all application resources in one big file to speed up the installation process? Sure we can with help of The Qt resource system. But there is one big disadvantage: whole resource file have to be loaded into process memory before you can access anything inside it. That means if you can't split your data between resource files and switch between them during application execution (most probably application logic doesn't allow that) you have to load all files in memory when application starts. In my case that was impossible to do because even EPOCSIZE tweaks couldn't help me to avoid *out of memory* crash.

Fortunately I had a deal with image files and found out that QML architects providently took care about overloading image providers in QML. Qt 4.7 contains a nice class called QDeclarativeImageProvider. It provides an interface for supporting pixmaps and threaded image requests in QML. In other words you can derive from that class, create own object from the derived class and attach it to QML engine with certain key (qstring) value. Every time QML engine try to resolve image source "image://you_key/somefile_id.jpg" it will invoke your object's method with somefile_id.jpg as parameter and will expect QImage or QPixmap in return.

So, the solution is obvious. All i need is to put all my image files in zip and implement my QDeclarativeImageProvider-derived class that could read images from the zip. I chose QuaZip library for reading zip's. Some code snippets are below. Also you can find sample project in the attachment.

Declaring our ImageReader class:

Its implementation:

Then it could be attached to the QML declarative engine (that should be done before you open any qml file in it):

Here images.zip is our data file and myzip - our keyword.

Now we can use any image from that zip in our qml file like that:

Normal 0 false false false RU X-NONE X-NONE

File 01_sdk_download_v4.jpg will be retrieved from the images.zip when necessary.

Sample project: ZIPDeclarativeImageProvider.zip

Many Nokia Store distributed applications have "Buy full version" or "Check our other apps" functionality which require opening of Nokia Store client app on certain page. Usually such functions could be implemented by opening store url in system browser. Browser will automatically redirect user to Nokia Store client and open required content or author page in it. But that approach has some disadvantages: (More)

Under cut you can find a video demonstration and source code of the small Qt app which is able to launch preinstalled Nokia Maps application and display a landmark with custom description in it. Tested with Maps 3.06 and N8-00. Sample can be easely ported back to Symbian C++.

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Few days ago I had a chance to play for a wile with my Nokia N950. I've tried to port some Qt application from Symbian to Harmattan and unfortunately faced with lack of support of QWidget and QGraphicsView based applications in that platform. Some of my findings are below: (More)

Hello,

Sometimes when you are working with video streaming in Qt usage of symbian realplayer for playing it might be the optimal solution.

There are 3 ways for launching system player with custom URL as a parameter in Qt: the right approach, the working approach and the new (for me) approach.

1. Right approach is to launch URL with QDesktopServices::openUrl() as described here. Thats how things should be done by Qt framework design. In fact QDesktopServices passing its parameter to system handler and system should decide what to do with it. So, "rtsp://" url schema should be opened in realplayer, "mailto:://" schema should launch the email service, "tel://" should launch phone dialer etc. But in Symbian^3 its not working as expected for most of URL schemas. For ex., "rtsp://" is not working. That should be fixed in Qt 4.7.2 - i already posted a bug in qt bugtracker for that (QTBUG-15136).
   
   But for URL schema (http://) it works. With one disadvantage: default "http://" handler is the system browser. So your URL will be opened in Web Browser and only after that browser will launch a system player. Same things can be achieved with better UX.
2. Working approach is to launch system media player directly and pass URL to it as parameter. That can be done from Symbian C++ code as described here. Instructions and sample Qt application are attached. Disadvantage of that approach is SwEvent capability requirement. That mean you'll need a DevCert certificate or pass Open Signed Online to try your app.
3. Recently i found 3rd way for launching URLs in system player from Qt: "Simply create a .ram file, for example foo.ram into file system. The file must contain nothing but the url of the video stream. Then simply open that file with QDesktopServices::openUrl(QUrl::fromLocalFile("c:\test.ram")) The source is on DiBo.Its really working at least for S^3 devices with both rtsp:// and http:// transports. I guess this is a preferable solution nowadays.  

P.S. For soultion for mailto:// schema take a look on QTBUG-15136.

instructions.txt

RTSPTest1.zip

headers.zip

Since developer.uiq.com is down for a long time, and there is no UIQ 3.x SDK copy on Sony Ericsson Developer World, i make bold to upload it to devmobile.ru

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Looks yesterday Symbian Foundation website was updated. As you can see in About:

This is an interim, placeholding website for the Symbian Foundation. We will be launching a full-scale online presence very shortly.

Much more interesting is a registration form in a Developers tab:

Interested in being among the very first developers to join the new Symbian Foundation developer program? Register your interest here and you'll be the first to hear as soon as we have news.

I'm very intrigued by that note. Does anybody know somehing about Symbian Foundation developer program?

 P.S. Today i got notification email about my reselection as FNC for that year. Thank you!

General , Futurology | Permalink | Comments (5) | Trackbacks (0)

Bridge between C/C++ and ActionScript 3.0

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