[composer] Make sure scalebars are updated during atlas previews

src/core/composer/qgscomposermap.cpp

@@ -635,6 +635,15 @@ void QgsComposerMap::setNewAtlasFeatureExtent( const QgsRectangle& extent )
   emit extentChanged();
 }
 
+void QgsComposerMap::toggleAtlasPreview()
+{
+  //atlas preview has been toggled, so update item and extents
+  mCacheUpdated = false;
+  updateItem();
+  emit itemChanged();
+  emit extentChanged();
+}
+
 QgsRectangle* QgsComposerMap::currentMapExtent()
 {
   //non-const version

src/core/composer/qgscomposermap.h

@@ -156,6 +156,9 @@ class CORE_EXPORT QgsComposerMap : public QgsComposerItem
     */
     void setNewAtlasFeatureExtent( const QgsRectangle& extent );
 
+    /**Called when atlas preview is toggled, to force map item to update its extent and redraw*/
+    void toggleAtlasPreview();
+
     /**Returns a pointer to the current map extent, which is either the original user specified
       extent or the temporary atlas-driven feature extent depending on the current atlas state of the composition.
       Both a const and non-const version are included.*/

src/core/composer/qgscomposerscalebar.cpp

@@ -164,7 +164,7 @@ void QgsComposerScaleBar::refreshSegmentMillimeters()
   if ( mComposerMap )
   {
     //get extent of composer map
-    QgsRectangle composerMapRect = mComposerMap->extent();
+    QgsRectangle composerMapRect = *( mComposerMap->currentMapExtent() );
 
     //get mm dimension of composer map
     QRectF composerItemRect = mComposerMap->rect();
@@ -181,7 +181,7 @@ double QgsComposerScaleBar::mapWidth() const
     return 0.0;
   }
 
-  QgsRectangle composerMapRect = mComposerMap->extent();
+  QgsRectangle composerMapRect = *( mComposerMap->currentMapExtent() );
   if ( mUnits == MapUnits )
   {
     return composerMapRect.width();

src/core/composer/qgscomposition.cpp

@@ -2345,6 +2345,11 @@ bool QgsComposition::setAtlasPreviewEnabled( bool e )
     }
   }
 
+  if ( mAtlasComposition.composerMap() )
+  {
+    mAtlasComposition.composerMap()->toggleAtlasPreview();
+  }
+
   update();
   return true;
 }