We continue with our project from the first map tutorial. What we want to do now is pretty simple: we want to be able to zoom in and out of the map with the help of two softkeys. Softkeys (usually two) are “buttons” that are placed in the lower area (corners) of a form.

Of course, the map control itself already provides some simple navigation functionality: you can drag the map to all sides and you can also zoom in and zoom out (just press long on the map: zooming will appear!). Nevertheless we want to be able to do that more user friendly: through the softkeys

For that purpose you will need to add those softkeys to the form first. As opposed to the usual buttons, softkeys are part of a form’s properties. You will see the relevant items right away!

Enable the softkeys and insert some meaningful values as text. Save the form – we are done here. Next switch over to the header of your app’s class. As described in another example, we will need to add some stuff in here so that the application itself can deal with the action events. Basically we need three things:

1. Define some constant integer values to identify the zooming actions
2. Inherit the app’s class also from the IActionEventListener
3. Implement the necessary handler for events OnActionPerformed()

const int BUTTON_ZOOM_IN = 1;
const int BUTTON_ZOOM_OUT = 2;

/**
 * [SimpleLocation] application must inherit from Application class
 * which provides basic features necessary to define an application.
 */
class SimpleLocation :
 public Application, IActionEventListener
{
    private:
        Frame *pFrame;
        Form *pForm;
        Map *pMap;

/**
 * Called when the battery level changes.
 */
 void OnBatteryLevelChanged(BatteryLevel batteryLevel);

 /**
 * Called when an action is performed
 */
 void OnActionPerformed(const Control& source, int actionId);

Next I have refactored the code from the previous example a little and put the initialization code into the corresponding function instead of keeping it in the OnForeground function. The drawing itself has been basically reduced to this:

void
SimpleLocation::OnForeground(void)
{
    RedrawMap();
}

void
SimpleLocation::RedrawMap(void)
{
    pMap->Draw();
    pFrame->Draw();
    pFrame->Show();

    return;
}

The rest has been transfered into the OnAppInitializing() function, where we also need to bind the action IDs for our zooming softkeys, as well as telling bada that the application’s class itself is going to deal with the action events.

bool
SimpleLocation::OnAppInitializing(AppRegistry& appRegistry)
{
    result r;
    String providerName = L"deCarta";
    String extraInfo = L"ClientName=yourlogin;ClientPassword=yourpass;HostUrl=http://ws.decarta.com/openls/openls";
    int width = 0;
    int height = 0;
    Coordinates center = Coordinates();
    center.Set(37.786505, -122.39862, 0);

    // bind the form and set it as current
    pFrame = this->GetAppFrame()->GetFrame();
    pForm = new Form();
    pForm->Construct("IDF_FORM1");
    pFrame->AddControl(*pForm);
    pFrame->SetCurrentForm(*pForm);

    // add action IDs and listeners to the soft keys
    pForm->SetSoftkeyActionId(SOFTKEY_0,BUTTON_ZOOM_IN);
    pForm->SetSoftkeyActionId(SOFTKEY_1,BUTTON_ZOOM_OUT);
    pForm->AddSoftkeyActionListener(SOFTKEY_0, *this);
    pForm->AddSoftkeyActionListener(SOFTKEY_1, *this);

    // Connect to OSP map service provider
    IMapServiceProvider* pProvider =
    static_cast<IMapServiceProvider*>(ProviderManager::ConnectToServiceProviderN
                            (providerName, LOC_SVC_PROVIDER_TYPE_MAP, extraInfo));
    if (null == pProvider) goto CATCH;

    // Create map
    pMap = new Map();
    if (null == pMap)  goto CATCH;

    // Specify map size (the whole space)
    // we take the whole available space on the form
    width=pForm->GetCanvasN()->GetBounds().width;
    height=pForm->GetCanvasN()->GetBounds().height;
    r = pMap->Construct(Osp::Graphics::Rectangle(0, 0, width, height), *pProvider);
    if (IsFailed(r)) goto CATCH;

    // Set desired zoom level
    r = pMap->SetZoomLevel(17, false);
    if (IsFailed(r)) goto CATCH;

    // Set center position to display
    r = pMap->SetCenter(center, false);
    if (IsFailed(r)) goto CATCH;

    // Enable my location
    pMap->SetMyLocationEnabled(true);

    // Render a map
    pForm->AddControl(*pMap);

    return true;

CATCH:
    delete pProvider;
}

Well, finally we only need to deal with the zooming events accordingly! It is all about modifying the map’s zoom level and redrawing it all. Please keep in mind that it is a quick&dirty solution meant to demonstrate not to teach – I do not check whether the zoom level crosses any limits in my code.

void
SimpleLocation::OnActionPerformed(const Control& source, int actionId)
{
    int zoomlevel = pMap->GetZoomLevel();
    switch (actionId)
    {
       case BUTTON_ZOOM_IN:
           zoomlevel++;
           pMap->SetZoomLevel(zoomlevel, true);
           RedrawMap();
           break;

       case BUTTON_ZOOM_OUT:
           zoomlevel--;
           pMap->SetZoomLevel(zoomlevel, true);
           RedrawMap();
           break;

       default:
           break;
    }
}

Build it, run it, enjoy it!

Related posts:

1. Displaying a Map in a bada application
2. Bada Example: Showing your location on the map
3. Bada how-to: map marker overlay