defaultServiceProvider::requestService(): no service found for - "org.qt-project.qt.camera"

this is my code

    Camera::Camera(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::Camera)
{
    ui->setupUi(this);
    mCamera = new QCamera(this);
    recorder = new QMediaRecorder(mCamera,this);
    mCameraViewfinder = new QCameraViewfinder(this);
    mCameraImageCapture = new QCameraImageCapture(mCamera,this);
    mLayout = new QVBoxLayout;

    mCamera->setViewfinder(mCameraViewfinder);
    mLayout->addWidget(mCameraViewfinder);
    ui->scrollArea->setLayout(mLayout);
    //mCameraViewfinder->show();
    mCamera->start();
}

Any help?