c++ qgisvector layer is not Valid

#include <QtCore>
#include <QApplication>
#include <QWidget>
#include <qgsapplication.h>
#include <QMainWindow>
#include <qgsmapcanvas.h>
#include <QVBoxLayout>
#include <qgsdatasourceuri.h>
#include <qgsmaplayerregistry.h>
#include <qgsvectorlayer.h>
#include <qgsvectordataprovider.h>


class PostGisViewer: public QMainWindow
{
public:
    PostGisViewer(): QMainWindow()
    {
        QWidget *w = new QWidget();
        this->setCentralWidget(w);
        QgsMapCanvas *canvas = new QgsMapCanvas(0,0);
        canvas->useImageToRender(false);
        QVBoxLayout *layout = new QVBoxLayout(w);
        layout->addWidget(canvas);
        QgsDataSourceURI uri;
        QgsVectorLayer layer("data/test.shp", "test", "ogr");
        QgsMapLayerRegistry::instance()->addMapLayer(&layer);
        QgsMapCanvasLayer cl(&layer);
        //QgsRectangle r(340000, 220000, 360000, 240000);
        //canvas->setExtent(r);
        qDebug() << layer.allFeatureIds();
        qDebug() << layer.isValid();
        qDebug() << layer.crs().isValid();
        qDebug() << layer.crs().authid();
        if (layer.isValid())
          {
            qDebug("Layer is valid");
          }
          else
          {
            qDebug("Layer is NOT valid");
          };
        qDebug() << "GeometryType: " << layer.geometryType();
    }
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QgsApplication::setPrefixPath("/usr/bin", true);
    QgsApplication::initQgis();
    PostGisViewer wnd;
    wnd.show();
    int retval = a.exec();
    QgsApplication::exitQgis();
    return retval;
}

I do not know, what do I do? Help me!