Use QgsFeedback instead of QProgressDialog for QgsVectorLayerExporter…

…::exportLayer

And add cancelation and progress reporting to background layer export

doc/api_break.dox

@@ -2190,7 +2190,8 @@ pointers makes for more robust, safer code. Use an invalid (default constructed)
 in code which previously passed a null pointer to QgsVectorLayerImport.
 - importLayer was renamed to exportLayer
 - The unused skipAttributeCreation in exportLayer() was removed
-- The unused QProgressBar argument in the QgsVectorLayerImport was removed
+- The QProgressDialog argument in exportLayer() was changed to a QgsFeedback object.
+- The unused QProgressDialog argument in the QgsVectorLayerImport was removed
 - ImportError was renamed to ExportError
 - The unused enum value ErrDriverNotFound was removed
 - hasError() was renamed to errorCode()

python/core/qgsvectorlayerexporter.sip

@@ -53,7 +53,7 @@ class QgsVectorLayerExporter : QgsFeatureSink
                                     bool onlySelected = false,
                                     QString *errorMessage /Out/ = 0,
                                     QMap<QString, QVariant> *options = 0,
-                                    QProgressDialog *progress = 0
+                                    QgsFeedback *feedback = 0
                                   );
 %Docstring
  Writes the contents of vector layer to a different datasource.
@@ -65,7 +65,7 @@ class QgsVectorLayerExporter : QgsFeatureSink
  \param onlySelected set to true to export only selected features
  \param errorMessage if non-null, will be set to any error messages
  \param options optional provider dataset options
- \param progress optional progress dialog to show progress of export
+ \param feedback optional feedback object to show progress and cancelation of export
  :return: NoError for a successful export, or encountered error
  :rtype: ExportError
 %End

src/core/qgsvectorlayerexporter.cpp

@@ -232,7 +232,7 @@ QgsVectorLayerExporter::exportLayer( QgsVectorLayer *layer,
                                      bool onlySelected,
                                      QString *errorMessage,
                                      QMap<QString, QVariant> *options,
-                                     QProgressDialog *progress )
+                                     QgsFeedback *feedback )
 {
   QgsCoordinateReferenceSystem outputCRS;
   QgsCoordinateTransform ct;
@@ -339,29 +339,25 @@ QgsVectorLayerExporter::exportLayer( QgsVectorLayer *layer,
   if ( !ct.isValid() )
     shallTransform = false;
 
-  int n = 0;
+  long n = 0;
+  long approxTotal = onlySelected ? layer->selectedFeatureCount() : layer->featureCount();
 
   if ( errorMessage )
   {
     *errorMessage = QObject::tr( "Feature write errors:" );
   }
 
-  if ( progress )
-  {
-    progress->setRange( 0, layer->featureCount() );
-  }
-
   bool canceled = false;
 
   // write all features
   while ( fit.nextFeature( fet ) )
   {
-    if ( progress && progress->wasCanceled() )
+    if ( feedback && feedback->isCanceled() )
     {
       canceled = true;
       if ( errorMessage )
       {
-        *errorMessage += '\n' + QObject::tr( "Import was canceled at %1 of %2" ).arg( progress->value() ).arg( progress->maximum() );
+        *errorMessage += '\n' + QObject::tr( "Import was canceled at %1 of %2" ).arg( n ).arg( approxTotal );
       }
       break;
     }
@@ -408,10 +404,11 @@ QgsVectorLayerExporter::exportLayer( QgsVectorLayer *layer,
     }
     n++;
 
-    if ( progress )
+    if ( feedback )
     {
-      progress->setValue( n );
+      feedback->setProgress( 100.0 * static_cast< double >( n ) / approxTotal );
     }
+
   }
 
   // flush the buffer to be sure that all features are written
@@ -495,7 +492,7 @@ bool QgsVectorLayerExporterTask::run()
 
   mError = QgsVectorLayerExporter::exportLayer(
              mLayer.data(), mDestUri, mDestProviderKey, mDestCrs, false, &mErrorMessage,
-             &mOptions );
+             &mOptions, mOwnedFeedback.get() );
 
   if ( mOwnsLayer )
     delete mLayer;

src/core/qgsvectorlayerexporter.h

@@ -75,7 +75,7 @@ class CORE_EXPORT QgsVectorLayerExporter : public QgsFeatureSink
      * \param onlySelected set to true to export only selected features
      * \param errorMessage if non-null, will be set to any error messages
      * \param options optional provider dataset options
-     * \param progress optional progress dialog to show progress of export
+     * \param feedback optional feedback object to show progress and cancelation of export
      * \returns NoError for a successful export, or encountered error
      */
     static ExportError exportLayer( QgsVectorLayer *layer,
@@ -85,7 +85,7 @@ class CORE_EXPORT QgsVectorLayerExporter : public QgsFeatureSink
                                     bool onlySelected = false,
                                     QString *errorMessage SIP_OUT = 0,
                                     QMap<QString, QVariant> *options = nullptr,
-                                    QProgressDialog *progress = nullptr
+                                    QgsFeedback *feedback = nullptr
                                   );
 
     /**