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<concept id="GUID-0C814ED6-3F64-4E0E-9C47-654AEDADBA90" xml:lang="en"><title>Going

Beyond Hello: A Tutorial for Symbian C++ Applications</title><shortdesc>This tutorial shows how you can extend that basic example to create

a small paint application, along the way learning more about the application

frameworks (e.g. defining menus, how to handle touch-screen events, drawing

to the screen etc.).</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>In the <xref href="GUID-301E5FAA-A1C3-4FD7-9D84-DAA61C66981B.dita">Symbian C++

Quick Start</xref> you learned how to create a basic example application using

Carbide.c++, and how to build and run it on the Windows emulator and on a

device.  </p>

<p><b>Comes with Code</b>: <xref href="http://developer.symbian.org/wiki/images/e/eb/HelloSymbianWorld_Example_Code.zip.dita">File:

HelloSymbianWorld Example Code.zip</xref></p>

<section id="GUID-14C6D367-D806-45F8-BC44-C5DBC78096D9">       <title> Application

Structure</title>       <p>Carbide.c++ offers two ways of exploring your project.

The traditional <b>Project Explorer</b> window, which can also be found in

Eclipse, lists the files belonging to the project in the same directory structure

as in the file system.  </p><p>The <b>Symbian Project Navigator</b> contains

the same contents, but displays them in a logical hierarchy according to <xref href="http://developer.symbian.org/wiki/index.php/Coding_Standards_and_Conventions.dita">Symbian

Conventions</xref>. </p><p> You might wonder why a basic "Hello World" application

contains so many files. The answer is straightforward - a much simpler Hello

World wouldn’t be a very good starting point for real-world applications.

 </p><p>Instead the wizard generates the project for a complete and readily

extensible application. The project separates code and data, and uses a form

of the <xref href="http://wiki.forum.nokia.com/index.php/Design_Patterns_in_Symbian.dita#http://wiki.forum.nokia.com/index.php/Design_Patterns_in_Symbian/Model-View-Control_Pattern">model

view controller pattern</xref> for structuring your code. The application

already reacts to system events and contains everything that is required for

localization. </p><p/><p><b>What are the directories of a project?</b><fig id="GUID-898488F8-5CF9-4A01-95F8-45E2C5D2E501">

<image href="GUID-FFC6F01E-15AB-43E6-90E8-0E42DA297AE9_d0e2166_href.png" placement="inline"/>

</fig></p><p/><b>\group</b><ul>

<li><p><b>bld.inf</b>: Component-definition file. This specifies the <codeph>mmp</codeph> files

that belong to your component, any shared header files that it exports, and

the default build targets (e.g. GCCE, WINSCW).</p><ul>

<li><p><codeph>Bld.inf</codeph> is used to generate the makefiles and <codeph>abld.bat</codeph> used

to build for the command-line (see <xref href="GUID-301E5FAA-A1C3-4FD7-9D84-DAA61C66981B.dita">Symbian

C++ Quick Start</xref>). </p></li>

<li><p>This file is the starting point when you want to import a Symbian C++

project into Carbide.c++, because it contains references to all executables

in your project (see the section on Importing Other Examples). </p></li>

</ul></li>

<li><p><b>HelloWorld.mmp</b>: Project-definition file. This specifies how

to build an executable (in this case <codeph>HelloWorld.exe</codeph>) in a

platform- and compiler-independent way. It contains information such as resource

files to be compiled, source files to include when compiling, and the libraries

to include when linking. </p></li>

<li><p><b>Icons_aif_scalable_dc.mk</b>: Makefile used to create the application's

icon from the <codeph>*.svg</codeph> file in the <codeph>/gfx</codeph> folder. </p></li>

</ul><p> </p><p><b>\src</b></p><ul>

<li><p> <b>HelloWorldApplication.cpp</b>: This file contains the entry point

for the EXE file (<codeph>E32Main()</codeph>) as well as the implementation

of the Application class (which provides some basic functionality for the

GUI framework). Normally this is "boilerplate" code and you do not need to

make any changes. </p></li>

<li><p><b>HelloWorldDocument.cpp</b>: This class is supposed to take care

of the persistent data model of your application and therefore provides some

functions to load and save <codeph>.ini</codeph> files. This mechanism is

disabled by default - for most applications you may treat this as "boilerplate"

code. </p></li>

<li><p><b>HelloWorldAppUi.cpp</b>: This is the main controller of your application.

It contains the logic for handling application-wide events (so you don’t have

to handle, for example, the exit event in every view). It owns all the views

that you use. </p></li>

<li><p><b>HelloWorldContainerView.cpp</b>: This is a kind of controller, which

is responsible for handling events and the UI elements of the currently visible

view. It’s not visible itself, but owns and manages the <i>Container</i> (below),

which corresponds to the view in the traditional model view controller pattern.</p></li>

<li><p><b>HelloWorldContainer.cpp</b>: Contains the UI elements that should

be displayed by the view. Therefore, the ContainerView and the Container usually

have a very strong relationship. </p></li>

</ul><p>During start-up, one class instance creates the next:</p><fig id="GUID-2A3EE3C2-3515-4217-BCB3-182A01936898">

<image href="GUID-AC3F5010-ECA6-4257-98B5-77FB26B4987F_d0e2272_href.png" placement="inline"/>

</fig><p/><p><b>\inc</b></p><ul>

<li><p><b>HelloWorldApplication.h</b>, <b>HelloWorldDocument.h</b>, <b>HelloWorldAppUi.h</b>, <b>HelloWorldContainerView.h</b>, <b>HelloWorldContainer.h</b>: Header files corresponding to each of the main source files above. </p></li>

<li><p><b>HelloWorld.hrh</b>: UIDs/identifiers for UI elements including views.

These are shared between the resource file definitions for UI elements and

the source code command handlers.</p></li>

<li><p><b>HelloWorld.pan</b>: Panic code and method definitions.</p></li>

</ul><p/><p><b>\data</b></p><ul>

<li><p><b>HelloWorld_reg.rss</b>: Contains registration information about

the application, such as its title.</p></li>

<li><p><b>HelloWorld.rss</b>: Main resource file. Contains additional information

about the application, as well as user interface and text resource definitions.

     </p></li>

<li><p><b>HelloWorld.loc</b>, <b>HelloWorld.l01</b>: Localization files. Strings

used by UI are defined in separate localization resource files. Each file

has the format <codeph>.lxx</codeph>, where <i>xx</i> is a language specific

numeric file extension - e.g. UK English is ‘01’, French ‘02’ and German ‘03’.

The <codeph>.loc</codeph> file is a kind of junction that <codeph>#includes</codeph> the

language specific files. The languages are compiled into separate resource

files (extension <codeph>.rxx</codeph>; the resource file for the current

language is loaded by the UI framework at runtime</p></li>

</ul><p/><p><b>\gfx</b></p><ul>

<li><p><b>list_icon.bmp</b>, <b>list_icon_mask.bmp</b>, <b>mark_icon.bmp</b>, <b>mark_icon_mask.bmp</b>:

Bitmap and bitmap masks. These are compiled into the MultiBitMap (<codeph>mbm</codeph>)

format for display in the application.</p></li>

<li><p> <b>qgn_menu_HelloWorld.svg</b>: SVG-T image that gets compiled into

the <codeph>HelloWorld_aif.mif</codeph> MultiImageFile (<codeph>mif</codeph>)

used for the application icon.</p></li>

</ul><p/><p><b>\sis</b></p><ul>

<li><p><b>HelloWorld.pkg</b>: Defines the contents that should be packaged

into the installable <codeph>.sis</codeph> file for the device. This includes

the executable as well as all resources required by the application (graphics

and so on).</p></li>

<li><p><b>HelloWorld.sis</b>: Compressed and self-contained installation file

for the device. Compiled based on the package file.     </p></li>

<li><p><b>HelloWorld.sisx</b>: <codeph>.sis</codeph> file which has been signed

with a certificate (in this case self-signed).</p></li>

</ul>     </section>

<section id="GUID-65BEDD17-334B-4C42-8D89-DAB355F97F51"><title> Extending

Hello World – Drawing</title><p>To make our application a little bit more

interactive, we are going to implement a simple paint tool, allowing the user

to draw lines by touching the screen.    </p><p>We could draw the lines directly

on the screen, but then everything would get lost when something caused our

application to redraw the screen – for example, a telephone call that came

through while our application was running. Therefore, we have to draw the

lines to a bitmap, which is simply copied to the screen whenever required.

  </p><p>Another solution (more difficult but also more flexible!) would be

to store all lines in a list and to iterate over the list each time the application

needs to draw the contents of the screen. </p></section>

<section id="GUID-217EFA6E-9B5F-4B65-8B99-E056CC26156D"><title> Using the

SDK Documentation</title><p>The class that can handle bitmap data is called <codeph>CFbsBitmap</codeph>.

Let’s take a look at the documentation for this class to find out more about

the required header files, libraries and available methods.    </p><p><xref href="http://developer.symbian.org/search/search_results.php?txtSearch=CFbsBitmap&amp;site=sdl_collection.dita">Search</xref> the

online documentation for the class you're interested in, in this case <codeph>CFbsBitmap</codeph>. <xref href="http://developer.symbian.org/main/documentation/reference/s%5E2/doc_source/reference/tb91sf-PP/fontandbitmapserver/index.html.dita">CFbsBitmap

in Os Font_and_Bitmap_Server</xref> should be (one of the) first topics you

find. </p><p/><note>If you're working offline you can also search for documentation

in the SDK. <b>Start</b> menu: <b>Start - S60 Developer Tools - 5th Edition

SDK, v<i>1.0</i> - SDK Documentation</b></note><p>Right at the top of the

reference page you will see that the header file we need to use is <codeph>FBS.H</codeph> and

the library we need to link against is called <codeph>fbscli.lib</codeph>. </p><fig id="GUID-23B3B7CF-E676-4FBC-8B26-E7B88764781C">

<image href="GUID-0B0EF90E-45A4-467F-8CD9-33FBC612B3BD_d0e2470_href.png" placement="inline"/>

</fig><p>This class is capable of storing a bitmap. It's also possible to

get direct access to the bitmap data. However for more convenient methods

of drawing we will work through a drawing device and context.    </p><p>To

find out more about bitmaps, contexts and drawing functions, <xref href="http://developer.symbian.org/search/search_results.php?txtSearch=bitmaps&amp;site=sdl_collection.dita">Search for ‘bitmaps’</xref> in the documentation, and go to the page <b>Bitmaps

in Using Bitmaps</b>, or <b>Using Bitmaps in Using Graphics Device Interfaces</b>.

   Symbian provides several different device and context classes. For our

application we’re going to use <codeph>CFbsBitmapDevice</codeph> (header file: <codeph>bitdev.h</codeph>,

library: <codeph>bitgdi.lib</codeph>) and <codeph>CFbsBitGc</codeph> (header

file: <codeph>bitstd.h</codeph>, library: <codeph>bitgdi.lib</codeph>). </p></section>

<section id="GUID-D9C51891-11DE-4042-AE32-CC7EA362C32A"><title> Adding Libraries

To a Project</title><p>In the previous step, we determined that we need two

libraries in order to use all three bitmap-related classes: <codeph>fbscli.lib</codeph> and <codeph>bitgdi.lib</codeph>.

To add them to our project, open the <codeph>HelloWorld.mmp</codeph> project

file (in the <codeph>/group/</codeph> folder if you’re using the <b>Project

Explorer</b> window). Switch to the <b>Libraries</b> tab.    At the top of

this page, you will see a list of included libraries. <codeph>fbscli.lib</codeph> is

already in the list, so we don’t need to add it. However <codeph>bitgdi.lib</codeph> is

missing. </p><note>There are more libraries in the list than are used by our

project (added by the wizard!). These cause no harm so we choose not to remove

them.</note><p>Click on the <b>Add</b> button. Search for <codeph>bitgdi.lib</codeph> in

the list and add it to the <b>Libraries</b> list. </p><fig id="GUID-7D1E15B4-5157-4F48-9084-6DDBD6EE0208">

<image href="GUID-E5FB2D04-D57E-4EEA-850F-40F813C75D8C_d0e2548_href.png" placement="inline"/>

</fig><p>When you’re finished, make sure that both libraries are in the <b>Libraries</b> list.

   </p><p>When you compile your application again, Carbide.c++ will detect

the changes in the .mmp file and ask you what to do. Click on <b>Compile and

Link</b> to update the project with the changes we have made to the <codeph>.mmp</codeph> file. <fig id="GUID-77F781CD-A2EF-4489-BAE2-EB283057670E">

<image href="GUID-10540A35-7E8E-40F0-BF93-CBC01884550C_d0e2565_href.png" placement="inline"/>

</fig></p></section>

<section id="GUID-F2A4FC0F-8C67-4151-8BD2-808FCEDD121F"><title> Creating Bitmaps</title><p>Now

the libraries have been added, we can use the bitmap classes in our project.

Open the file <codeph>HelloWorldContainer.h</codeph> and add the following

include statements: </p><codeblock xml:space="preserve">#include &lt;fbs.h&gt;

#include <bitdev.h>

#include <bitstd.h>

</codeblock><p>We also need to store the bitmap objects as instance (member)

variables. Add the following definitions to a private section of the <codeph>CHelloWorldContainer</codeph> class.

Be careful not to write anything into areas managed by the UI designer, because

your changes could be overwritten. These areas are marked by comments.   

 </p><codeblock xml:space="preserve">private:  

CFbsBitmap* iBitmap;  

CFbsBitmapDevice* iBmpDevice;  

CFbsBitGc* iBmpGc;   </codeblock><p>Symbian C++ uses some <xref href="http://developer.symbian.org/wiki/index.php/Coding_Standards_and_Conventions.dita#http://developer.symbian.org/wiki/index.php/Coding_Standards_and_Conventions/Naming_Conventions">naming conventions</xref>. Instance variables should have a lowercase <codeph>i</codeph> at

the beginning of the variable name (<codeph>iBitmap</codeph>). Arguments should

be marked by an a (<codeph>aBitmap</codeph>). Normal local variables that

you create inside a function do not need any prefix. That way, you instantly

know where the variable is coming from – this is very important when deleting

objects.    Next, we want to create the bitmap. Define and implement a new

method: </p><codeph>void CHelloWorldContainer::CreateBitmapsL()</codeph><p>Let’s

go line by line through the required code for this method:    First, we have

to make sure that any previous objects are deleted if they already exist.

This would be required (for example) if the running application needs to re-create

the bitmap because the screen layout changes. You don’t need to add an if

statement to check if the pointer is NULL beforehand – the C++ <codeph>delete</codeph> statement

only deletes the object if the pointer is not NULL. You do however need to

ensure that the objects are set to NULL after deletion to avoid possible "double

deletion" in the destructor. </p><codeblock xml:space="preserve">delete iBitmap; iBitmap = NULL;  

delete iBmpDevice; iBmpDevice = NULL;  

delete iBmpGc; iBmpGc = NULL;</codeblock><p>This following line of code should

look familiar – it simply creates an instance of the <codeph>CFbsBitmap</codeph> class:

     </p><p><codeph> iBitmap = new (ELeave) CFbsBitmap();</codeph>       </p><p>The

(<codeph>ELeave</codeph>) parameter is Symbian C++ specific. This causes a <xref href="http://developer.symbian.org/wiki/index.php/Leaves_%26_The_Cleanup_Stack_(Fundamentals_of_Symbian_C%2B%2B).dita"> leave</xref> (the

Symbian C++ equivalent of standard exceptions) if allocating the object fails

– for example, because there is not enough free memory. With the (<codeph>ELeave</codeph>),

you don’t have to manually check if the pointer is actually pointing to a

valid object after creating the object instance. You can find out more about

leaves in <xref href="http://developer.symbian.org/wiki/index.php/Fundamentals_of_Symbian_C%2B%2B.dita">Fundamentals

of C++</xref>.    </p><p>We do not handle the potential leave here; that’s

why the method name (<codeph>CreateBitmapL()</codeph>) has a trailing L to

show that it can also leave. More on this topic in a moment.    </p><p>Now,

it’s time to let the <codeph>CFbsBitmap</codeph> class allocate the memory

for the bitmap it is going to manage. The available drawing size for our container

can be queried by the method <codeph>Size()</codeph> from its base class. <codeph>EColor16MU</codeph> specifies

the color depth – in this case, it’s a true color display mode with 32 bits

per pixel; the top byte is unused. The color mode <codeph>EColor16MA</codeph> would

use the top byte for the alpha channel, several other modes are available

as well.   </p><p><codeph>iBitmap-&gt;Create(Size(), EColor16MU);</codeph>  

 </p><p>The next line creates a graphics device based on the bitmap. A graphics

device represents the medium being drawn to and is needed to create a graphics

context. The use of a <codeph>NewL()</codeph> method is common in Symbian

C++; it is a static factory function which returns a fully constructed object

of the desired type.   </p><p><codeph> iBmpDevice = CFbsBitmapDevice::NewL(iBitmap);</codeph> 

  </p><p>A graphics context provides a large number of drawing operations,

along with state settings defining how the drawing is performed. The bitmap

graphics context used here is a specialization of the generic graphics context

and adds some methods that can be used for bitmaps only – such as clearing

and copying rectangular areas.    </p><p><codeph>iBmpDevice-&gt;CreateContext(iBmpGc);</codeph> 

  </p><p>Whenever you create objects, it’s best to think about where and when

they are going to be deleted right away. Memory leaks are a serious issue

on a mobile device where no virtual memory is available and the main memory

is limited to 30-80 MB. Therefore, go to the destructor of <codeph>CHelloWorldContainer</codeph> and

add the required statements for deleting the three objects:      </p><p> <codeblock xml:space="preserve">delete iBmpGc;  

delete iBmpDevice;  

delete iBitmap;</codeblock>       </p><p>The next step addresses the remaining

question: where to call the <codeph>CreateBitmapsL()</codeph> method. Of course,

you could do this from the construction methods of the class. But what if,

while your application is running, the user physically turns the phone, causing

it to switch from portrait to landscape mode? Because the bitmap was created

with the portrait size in mind, the user would no longer be able to use the

full screen for drawing.    </p><p>Therefore, we have to react to events that

inform us when the screen size is changed. In those situations, <codeph>SizeChanged()</codeph> is

executed. When the container is first constructed, its size changes as well.

Because of this, we can simply call our <codeph>CreateBitmapsL()</codeph> method

from within <codeph>SizeChanged()</codeph>:       </p><p><codeblock xml:space="preserve">void CHelloWorldContainer::SizeChanged()  

	{  

	CCoeControl::SizeChanged();  

	LayoutControls();     

	// [[[ begin generated region: do not modify [Generated Contents]

	// ]]] end generated region [Generated Contents]

	if (!iBitmap || (iBitmap && iBitmap->SizeInPixels() != Size()))

		{

		TRAPD(err, CreateBitmapsL());

		}

	}</codeblock>      </p><p>In the source code above, an additional check ensures

that the bitmap is only re-created if the size available for the container

is really different to the existing bitmap size – the <codeph>SizeChanged()</codeph> method

is also called, for example, when the option menu obscures part of our view.

This does not affect the available space for our drawing area and therefore

should not lead to re-creating the bitmap.    </p><p>But what is the <codeph>TRAPD()</codeph> statement

doing here? Let’s use this to take a closer look at the concept of leaves. </p><p/><p><b>Leaves</b></p><p>When

programming using Symbian C++, an L is appended to the name of methods that

can leave (usually because it contains other methods that can leave and does

not choose to "TRAP" them). Note: this is a helpful convention, but is not

checked or required by the compiler.    </p><p>Our <codeph>CreateBitmapsL()</codeph> method

contains two methods that can leave: the (<codeph>ELeave</codeph>) parameter

causes a leave if there is not enough memory to allocate the object. The <codeph>NewL()</codeph> method

from the graphics device also has a trailing <codeph>L</codeph> – meaning

that this method can also leave. We did not catch any (all) of those leaves

in the <codeph>CreateBitmapsL()</codeph> method so it was named with a trailing <codeph>L</codeph>.

   </p><p>Any leaves are passed up in the call stack until caught by a <codeph>TRAPD</codeph> macro.

The <codeph>SizeChanged()</codeph> method traps any leaves from <codeph>CreateBitmapsL()</codeph> and

consequently does <b>not</b> need to have a trailing <codeph>L</codeph>. 

  </p><p>The error code of the leave is stored in the err variable, which

is declared as a normal integer by this macro. It would be a good idea to

take a look at the contents of this variable and to handle errors instead

of ignoring them as we’re doing here. But for the sake of simplicity, we do

not handle any errors that might occur in this situation. </p><p/><p><b>Tip</b></p><p>A

good way to automatically check your code for potential problems is to use

the <i>CodeScanner</i> tool that comes with Carbide.c++. It is a static code-analysis

tool looking at Symbian coding rules and standards. Find out more at: <xref href="http://carbidehelp.nokia.com/help/topic/com.nokia.carbide.cpp.codescanner/html/codescanner.htm.dita">http://carbidehelp.nokia.com/help/topic/com.nokia.carbide.cpp.codescanner/html/codescanner.htm</xref></p></section>

<section id="GUID-7E4A9491-8F22-4D68-9890-95332D31412B"><title> Handling Touch

Events</title><p>Before we start handling the touch events, we need one more

instance variable in our code. To draw a line from one touch position to the

next, it’s necessary to save the first position. Therefore, add the following

private instance variable to <codeph>CHelloWorldContainer</codeph>: <codeblock xml:space="preserve">TPoint iLastPos;</codeblock></p><p><codeph>TPoint</codeph> is

a convenience class that stores two integers that can be used as co-ordinates.

Additionally, it provides some methods to modify the point. We do not need

to initialize the variable in the constructor of the <codeph>CHelloWorldContainer</codeph> class

– the container class is indirectly derived from the class <codeph>CBase</codeph>,

which automatically zero-initializes all member variables.    Touch events

are delivered to the container class, which is responsible for managing the

visible UI content in the main pane of your application. To handle the events

ourselves, we have to override the following method in <codeph>CHelloWorldContainer</codeph>: </p><p><codeph>void

CHelloWorldContainer::HandlePointerEventL(const TPointerEvent&amp; aPointerEvent)</codeph></p><p>Define

this method in the header file (can be private or protected) and add its implementation

in the <codeph>.cpp</codeph> file.    The information about the new event

is sent through the argument <codeph>aPointerEvent</codeph>. We are interested

in the up event for the first button (there is only one in current touch devices;

you can’t click with a right button as you would with a mouse). Whenever the

user releases the stylus or finger from the touch screen, we want to draw

a line to this position. Put the following code into this if statement: <codeblock xml:space="preserve">if (aPointerEvent.iType == TPointerEvent::EButton1Up)

  {

  }</codeblock></p><p>Drawing the line itself is rather simple. First, define

the color and style that should be used for drawing, then call the function

for drawing the line. Note that the settings concerning the color and style

stay active until they are changed again in this graphics context – you do

not need to set them every time when executing consecutive drawing operations. </p><codeblock xml:space="preserve">iBmpGc-&gt;SetPenColor(KRgbRed);  

iBmpGc->SetPenSize(TSize(2,2));  

iBmpGc-&gt;DrawLine(iLastPos, aPointerEvent.iPosition);</codeblock><p>Next, we

have to save the new position, because it will be required as the starting

point for the next line. </p><codeph>iLastPos = aPointerEvent.iPosition;</codeph><p>Finally,

issue a request to the framework to redraw the screen. Otherwise, the user

won’t see the new line! </p><codeph>DrawDeferred();</codeph><p>At the end

of the method, also call the <codeph>HandlePointerEventL()</codeph> method

of the base class (the container is derived from <codeph>CCoeControl</codeph>,

because it is a normal UI control by itself): </p><codeph>CCoeControl::HandlePointerEventL(aPointerEvent);</codeph><p>To

sum it up, this is the final code for the <codeph>HandlePointerEvent()</codeph> method: </p><codeblock xml:space="preserve">void CHelloWorldContainer::HandlePointerEventL(const TPointerEvent&amp; aPointerEvent)

    {

    if (aPointerEvent.iType == TPointerEvent::EButton1Up)

      {

      iBmpGc->SetPenColor(KRgbRed);

      iBmpGc->SetPenSize(TSize(2,2));

      iBmpGc->DrawLine(iLastPos, aPointerEvent.iPosition);

      iLastPos = aPointerEvent.iPosition;

      DrawDeferred();

      }

    CCoeControl::HandlePointerEventL(aPointerEvent);

    }</codeblock><p>We’ve already added all the code required for drawing

to the bitmap, but this bitmap still has to be transferred to the screen.

The <codeph>CHelloWorldContainer::Draw()</codeph> method is called when the

system wants the contents of the container to be redrawn. Therefore, we need

to add the following line of code to the end of the <codeph>Draw()</codeph> method,

which copies the bitmap to the top left of the graphics context of the screen: </p><codeph>gc.BitBlt(TPoint(0,

0), iBitmap);</codeph><p>Now compile the project. It should already work –

you can draw red lines by just clicking inside the main pane of the emulator! </p><fig id="GUID-CFD29EE4-464B-498C-80F5-493847DE0AEE">

<image href="GUID-700CD2E2-DBB7-40BD-BC6D-9BC79C5A0BBF_d0e2845_href.png" placement="inline"/>

</fig></section>

<section id="GUID-8DC096A0-807D-437C-9A96-ABAFE2AF7F26"><title>  Defining

a Menu </title><p>The application would be improved if the user could clear

the drawing during use, rather than having to restart it. This section shows

how you add and handle menu items to provide this functionality, and to exit

the application    Open the <codeph>HelloWorldContainer.uidesign</codeph> document.

You can find it in the root folder of your project in the <b>Project Explorer</b> or

in the <b>UI Designs</b> folder of the Symbian Project Navigator.    </p><p>Click

on the <b>Options</b> menu item below the UI design to reveal the menu. As

indicated, you simply need to click on the empty menu item and start typing. </p><fig id="GUID-96D944A2-87C5-4530-AB0C-580C3277285D">

<image href="GUID-20FEEF54-23CB-4D30-B846-11B4ACE8E772_d0e2869_href.png" placement="inline"/>

</fig><p>Add two menu items – <b>Clear</b> (for clearing the image) and <b>Exit</b> (for

closing the application).    </p><p>Then click once on the Exit menu item

to select it. Go to the <b>Behavior</b> group of the <b>Properties</b> window

and change the command ID to <codeph>EAknCmdExit</codeph> (this is available

in the drop-down list). This command will also be sent to your application

if the operating system wants to shut it down, for example, when the phone

does not have enough memory left. Therefore, it is necessary that every application

always responds to this event and instantly shuts the application down. It

is already handled by the basic application that the Carbide.c++ wizard generated

for you; you don’t need to implement the command handling for this event yourself. </p><fig id="GUID-8FD2973F-23FF-4734-AE16-CA39C02C7DE5">

<image href="GUID-D7F000F0-019A-486E-BB0C-C0065D08C5F6_d0e2892_href.png" placement="inline"/>

</fig><p>If you try your application now, you will see that the Exit menu

item already works. </p><p/><p><b>Tip</b></p><p> When testing the application,

always quit your application using the <b>Exit</b> command (rather than just

closing the emulator). The application environment will then automatically

check for memory leaks. If you just shut down the emulator you may not discover

the leak until much later, making it a lot more difficult to find the cause.</p></section>

<section id="GUID-0090F731-A243-44C7-96ED-1EC5DB172F8D"><title> Clearing the

Drawing </title><p>Whenever the <b>Clear</b> menu item is selected the view

class method <codeph>CHelloWorldContainerView::HandleCommandL()</codeph> is

called with the command ID of the menu item as a parameter.   </p><p> If we

want to handle the menu item, the UI designer can create the necessary code

for us. Right-click on the menu item and choose <b>Handle ‘selected’ Event</b>.

The UI designer will ask you to save the design – choose <b>Yes</b>. The code

will then be generated and you will jump into the code view to a new method

called <codeph>HandleClearMenuItemSelectedL()</codeph> – a more convenient

place to put your command-handling code than directly in a big <codeph>HandleCommandL()</codeph> method

that receives all commands. The auto-generated source code therefore calls

the new extra method from within <codeph>HandleCommandL()</codeph> (take a

look at that method to see what really happens). </p><fig id="GUID-8E944FEE-EFDF-4AFE-BEB8-F3B216B91A98">

<image href="GUID-881C353C-6482-4DFE-9D43-CFB80DEB77A5_d0e2936_href.png" placement="inline"/>

</fig><p>Now, we only need to tell the container that it should clear its

bitmap buffer. To do this, create a new public method in the container: </p><codeblock xml:space="preserve">void CHelloWorldContainer::ClearDrawing()

  {

  iBmpGc->Clear();

  DrawDeferred();

  }</codeblock><p>Now, call this method from the menu item handler method.

As explained in the section about the application architecture, the view class

(<codeph>CHelloWorldContainerView</codeph>) is the controller and owner for/of

the container class (<codeph>CHelloWorldContainer</codeph>). Therefore, this

class has a pointer to the container as an instance variable, which you can

use to clear the drawing. </p><codeblock xml:space="preserve">TBool CHelloWorldContainerView::HandleClearMenuItemSelectedL(TInt aCommand)

  {

  iHelloWorldContainer->ClearDrawing();

  return ETrue;

  }</codeblock><p>The menu command should now clear the image.    </p><p>Congratulations,

you have completed the tutorial and have created your own small mobile painting

application! </p></section>

<section id="GUID-2BD775FF-BD36-4550-A388-48A3B1832D9E"><title> Further Exercises</title><p>As

an exercise, it’s a good idea to extend the application by yourself – for

example, you could add some menu items that allow the end user to change the

color of the pen. </p><p/><p><b>Tip</b></p><p> It’s a good idea to learn

keyboard shortcuts as early as possible, because they can significantly increase

the efficiency of your work. For example, you can press <b>Ctrl + B</b> to

build the project, instead of using the icon or the menu commands. Also very

helpful: <b>Ctrl + Shift + F</b> automatically formats and indents your code.

You can get a full list of commands by pressing <b>Ctrl + 3</b>. A hot keys

list appears when you press <b>Ctrl + Shift + L</b>.</p><p/><p> <b>Importing

Other Examples</b></p><p>The S60 SDK itself installs many examples; additional

applications can be downloaded from the developer.symbian.org and Forum Nokia

(see the Related Info section  for more information).    To import ready-made

applications in Carbide.c++, go to <b>File | Import</b>. In the following

dialog, select <b>Symbian OS Bld.inf file</b> and click <b>Next</b>. </p><fig id="GUID-8E8F4507-70E7-496C-AE4D-16DAD8146ABA">

<image href="GUID-631E27DB-97A7-47E2-8FC1-856198435FFF_d0e2998_href.png" placement="inline"/>

</fig><p/><p>Now, click <b>Browse</b> and navigate to the <codeph>bld.inf</codeph> file

of the project you want to import. It’s usually stored in the <codeph>/group/</codeph> subfolder

of the project. </p><fig id="GUID-B682943D-10EE-4DC8-B510-7C2D54C536EE">

<image href="GUID-C588B869-6940-42B2-84F9-71467F6A4306_d0e3014_href.png" placement="inline"/>

</fig><p>In the following step, select which SDKs you would like to use. The

same considerations as those explained when creating your Hello World application

apply. </p><fig id="GUID-5A381CA4-CCE0-4359-8F02-697AEDA72BDE">

<image href="GUID-D492CF6C-F889-4299-AC75-951EF343AC9F_d0e3020_href.png" placement="inline"/>

</fig><p>You can usually accept the default values for the next step and let

the wizard import everything.    </p><p>In the last step, you have to define

the <b>Project Properties</b>. In most cases, you can leave the default values. </p><fig id="GUID-1AB6D789-9407-4AB0-8F52-B1138DE063BD">

<image href="GUID-F18A6C91-136D-450E-90F0-7C2B9263777C_d0e3031_href.png" placement="inline"/>

</fig><p>Afterwards, the project is imported and you can start working. The

project contents will not be copied to the current Carbide.c++ workspace,

so you will work directly on the original directory and the original files.

Copy the project to a different directory first if you want to keep the original

project or example in its original state – for example, into the workspace

directory.    </p><p><b>Troubleshooting</b>: If <keyword>importing</keyword> the

project fails, take special care of the last step of the import process: the

root directory should be set correctly to the root directory of the project

and not one level above it. Also, the project name should be the same as the

last part of the root directory. From time to time, the default values are

not configured properly, causing problems in the import process. </p><p/><p><b>Warning</b>  </p><p>Do

not use the standard (Eclipse) project import! The reason is that this import

method would also import all build configuration settings, including references

to installed SDKs and paths on the original system. Therefore, if you import

a project from somebody else but don’t have the SDK installed in exactly the

same directory, the build configurations will no longer work. The <codeph>bld.inf</codeph> import

method recreates the SDK bindings and only imports the real contents of the

project.</p></section>

<section id="GUID-191D5D9D-00FB-47F0-B88B-8B87588A20C8"><title> Summary</title><p>This

part of the tutorial has shown how we can extend the basic skeleton from the <xref href="GUID-301E5FAA-A1C3-4FD7-9D84-DAA61C66981B.dita">Symbian C++ Quick Start</xref> to

create a small paint application. The tutorial explains the application framework,

including how you define menus, how to handle touch-screen events, drawing

to the screen etc. </p></section>

<section id="GUID-8B6E602D-CA6B-41DD-B3DC-4C3BC9A04154"><title> Related Info</title><ul>

<li><p><xref href="GUID-301E5FAA-A1C3-4FD7-9D84-DAA61C66981B.dita">Symbian C++

Quick Start</xref></p></li>

<li><p><xref href="http://developer.symbian.org/wiki/index.php/Getting_Started_with_Debugging_on_the_Device.dita">Getting

Started with Debugging on the Device</xref></p></li>

<li><p><xref href="http://developer.symbian.org/wiki/images/e/eb/HelloSymbianWorld_Example_Code.zip.dita">File:

HelloSymbianWorld Example Code.zip</xref>  (code example associated with this

article)</p></li>

</ul></section>