How to make rectangle selection on QgsMapCanvas?

Question

I have this code for create and open raster map:

if(QFile::exists(rasterFileName))
{
    QFileInfo myRasterFileInfo(rasterFileName);
    m_pRasterLayer = QSharedPointer<QgsRasterLayer>(
        new QgsRasterLayer(myRasterFileInfo.filePath(), 
        myRasterFileInfo.completeBaseName()));

    if (m_pRasterLayer->isValid())
    {
        QgsMapLayerRegistry::instance()->addMapLayer(
            m_pRasterLayer.data(), true);

        QList<QgsMapCanvasLayer> layerList;
        layerList.append(QgsMapCanvasLayer(m_pRasterLayer.data(), true));

        m_pMapCanvas->setLayerSet(layerList);

        /* ... */
    }
}

How can I make (write code for) rectangle selection by mouse on my map?

Answer 1

If I got you right, you can have a look at the source code of the class QgsMapToolSelectRectangle to get an idea of how to select by rectangle on your map.

QgsMapToolSelectRectangle allows you to get a rectangle from mouse events, draw it as a rubber band on the QgsMapCanvas and perform a select operation on your data.

This code snippet performs the selection:

  if ( mRubberBand )
  {
    QgsMapToolSelectUtils::setRubberBand( mCanvas, mSelectRect, mRubberBand );

    QgsGeometry* selectGeom = mRubberBand->asGeometry();
    if ( !mDragging )
    {
      bool doDifference = e->modifiers() & Qt::ControlModifier ? true : false;
      QgsMapToolSelectUtils::setSelectFeatures( mCanvas, selectGeom, false, doDifference, true );
    }
    else
      QgsMapToolSelectUtils::setSelectFeatures( mCanvas, selectGeom, e );

    delete selectGeom;

    mRubberBand->reset( QGis::Polygon );
    delete mRubberBand;
    mRubberBand = 0;
  }

As you can see, it relies on the class QgsMapToolSelectUtils, which does the work from line 138 on (setSelectFeatures() method):

QgsFeatureIterator fit = vlayer->getFeatures( QgsFeatureRequest().setFilterRect( selectGeomTrans.boundingBox() ).setFlags( QgsFeatureRequest::ExactIntersect ).setSubsetOfAttributes( QgsAttributeList() ) );

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By the way, no idea of your use case, but why not doing it in Python? Are you developing a C++ core plugin?