[Qgis-user] Question

[Richard Duivenvoorde]

Hi,

FYI These kind of developers/c++ questions are problably better asked/answered on the QGIS-dev list

I think you also should add some more context, for example: 
- what exactly are you trying to do? Add a rasterlayer to... what?
- which development/Operating system environment are you using for this?
- is this a standalone dir applicatio?
- is this code somewhere on github so others can have a look?

Otherwise this is too open I think, for others to take the time to try to understand and answer.

Regards,

Richard Duivenvoorde




On 7/21/20 1:18 PM, Alireza Ghalavand wrote:
> Hello,
> 
> 
>   Qgis Error “Raster layer Cannot instantiate the 'gdal' data provider” in qt c++ <https://stackoverflow.com/questions/63010283/qgis-error-raster-layer-cannot-instantiate-the-gdal-data-provider-in-qt-c>
> 
> When I am trying to add a raster layer, I get this error from QgsRasterLayer::IsValid()!!! Can anybody tell me why this happens!? I am beginner in qgis, so could you please explain in detail. the first func "onAddLayer" used for Add button clicked and second func is defined for adding a raster layer.
> 
> *my code:*
> void  MainWindow::onAddLayer()
> {
>   const auto  path = QFileDialog::getOpenFileName(this, "SELECT GIS MAP LAYER", QDir(
>                                                     _lastMapDir).path());
> 
>   if (path.isEmpty() || path.isNull())
>   {
>     return;
>   }
> 
>   addRasterLayer(path);
>   _lastMapDir = QDir(path).canonicalPath();
> }
> 
> void  MainWindow::addRasterLayer(const QFileInfo &info)
> {
>   LOG(QString("adding map layer %1").arg(info.filePath()));
>   QString  errMsg;
> 
> //  if (!QgsRasterLayer::isValidRasterFileName(info.filePath(), errMsg))
> //  {
> //    LOG(errMsg);
> 
> //    return;
> //  }
> 
>   QScopedPointer<QgsRasterLayer>  layer(new QgsRasterLayer(info.filePath(), info.baseName()));
>   //layer->setDataProvider("gdal"); // Added by ArGhalavand
> 
>   if (!layer->isValid())
>   {
>     LOG(QString("failed to add layer (%1)").arg(layer->error().message(
>                                                   QgsErrorMessage::Format::Text)));
> 
>     return;
>   }
> 
>   save("last_layer_path", info.filePath(), "gis");
>   _rasterProvider = layer->dataProvider();
>   _mapCanvas->freeze(true);
>   auto  item = QgsMapCanvasLayer(layer.take(), true);
>   _mapCanvas->setExtent(item.layer()->extent());
>   QgsMapLayerRegistry::instance()->addMapLayer(item.layer(), true);
>   _mapCanvas->setLayerSet(QList<QgsMapCanvasLayer>() << item);
>   _mapCanvas->freeze(false);
>   _mapCanvas->setVisible(true);
>   _mapCanvas->refresh();
>   statusBar()->showMessage(QString("%1 LOADED").arg(info.fileName()), 3000);
> }
> 
> *With Best Regards,*
> Alireza Ghalavand
> 
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