Add a signal to QgsProject for when project color scheme changes

python/core/auto_generated/qgsproject.sip.in

@@ -1003,6 +1003,15 @@ in the project. The removeMapLayer(), removeMapLayers() calls do not block remov
 .. deprecated:: since QGIS 3.4 use QgsMapLayer.setFlags() instead
 
 .. versionadded:: 3.2
+%End
+
+    void setProjectColors( const QgsNamedColorList &colors );
+%Docstring
+Sets the ``colors`` for the project's color scheme (see QgsProjectColorScheme).
+
+.. seealso:: :py:func:`projectColorsChanged`
+
+.. versionadded:: 3.6
 %End
 
     void generateTsFile( const QString &locale );
@@ -1230,6 +1239,15 @@ Emitted when the project's metadata is changed.
 .. versionadded:: 3.2
 %End
 
+    void projectColorsChanged();
+%Docstring
+Emitted whenever the project's color scheme has been changed.
+
+.. seealso:: :py:func:`setProjectColors`
+
+.. versionadded:: 3.6
+%End
+
 
     void layersWillBeRemoved( const QStringList &layerIds );
 %Docstring

src/core/qgscolorscheme.cpp

@@ -221,21 +221,7 @@ bool QgsProjectColorScheme::setColors( const QgsNamedColorList &colors, const QS
 {
   Q_UNUSED( context );
   Q_UNUSED( baseColor );
-
-  // save colors to project
-  QStringList customColors;
-  QStringList customColorLabels;
-
-  QgsNamedColorList::const_iterator colorIt = colors.constBegin();
-  for ( ; colorIt != colors.constEnd(); ++colorIt )
-  {
-    QString color = QgsSymbolLayerUtils::encodeColor( ( *colorIt ).first );
-    QString label = ( *colorIt ).second;
-    customColors.append( color );
-    customColorLabels.append( label );
-  }
-  QgsProject::instance()->writeEntry( QStringLiteral( "Palette" ), QStringLiteral( "/Colors" ), customColors );
-  QgsProject::instance()->writeEntry( QStringLiteral( "Palette" ), QStringLiteral( "/Labels" ), customColorLabels );
+  QgsProject::instance()->setProjectColors( colors );
   return true;
 }
 

src/core/qgsproject.cpp

@@ -52,6 +52,7 @@
 #include "qgsmaplayerstore.h"
 #include "qgsziputils.h"
 #include "qgsauxiliarystorage.h"
+#include "qgssymbollayerutils.h"
 
 #include <QApplication>
 #include <QFileInfo>
@@ -713,6 +714,7 @@ void QgsProject::clear()
   mArchive->clear();
 
   emit labelingEngineSettingsChanged();
+  emit projectColorsChanged();
 
   // reset some default project properties
   // XXX THESE SHOULD BE MOVED TO STATUSBAR RELATED SOURCE
@@ -1378,6 +1380,7 @@ bool QgsProject::readProjectFile( const QString &filename )
   emit readProjectWithContext( *doc, context );
   emit snappingConfigChanged( mSnappingConfig );
   emit topologicalEditingChanged();
+  emit projectColorsChanged();
 
   // if all went well, we're allegedly in pristine state
   if ( clean )
@@ -2942,6 +2945,25 @@ void QgsProject::setRequiredLayers( const QSet<QgsMapLayer *> &layers )
   }
 }
 
+void QgsProject::setProjectColors( const QgsNamedColorList &colors )
+{
+  // save colors to project
+  QStringList customColors;
+  QStringList customColorLabels;
+
+  QgsNamedColorList::const_iterator colorIt = colors.constBegin();
+  for ( ; colorIt != colors.constEnd(); ++colorIt )
+  {
+    QString color = QgsSymbolLayerUtils::encodeColor( ( *colorIt ).first );
+    QString label = ( *colorIt ).second;
+    customColors.append( color );
+    customColorLabels.append( label );
+  }
+  writeEntry( QStringLiteral( "Palette" ), QStringLiteral( "/Colors" ), customColors );
+  writeEntry( QStringLiteral( "Palette" ), QStringLiteral( "/Labels" ), customColorLabels );
+  emit projectColorsChanged();
+}
+
 void QgsProject::generateTsFile( const QString &locale )
 {
   QgsTranslationContext translationContext;

src/core/qgsproject.h

@@ -47,6 +47,7 @@
 #include "qgstranslationcontext.h"
 #include "qgsprojecttranslator.h"
 #include "qgsattributeeditorelement.h"
+#include "qgscolorscheme.h"
 
 class QFileInfo;
 class QDomDocument;
@@ -1001,6 +1002,14 @@ class CORE_EXPORT QgsProject : public QObject, public QgsExpressionContextGenera
      */
     Q_DECL_DEPRECATED void setRequiredLayers( const QSet<QgsMapLayer *> &layers );
 
+    /**
+     * Sets the \a colors for the project's color scheme (see QgsProjectColorScheme).
+     *
+     * \see projectColorsChanged()
+     * \since QGIS 3.6
+     */
+    void setProjectColors( const QgsNamedColorList &colors );
+
     /**
      * Triggers the collection strings of .qgs to be included in ts file and calls writeTsFile()
      * \since QGIS 3.4
@@ -1201,6 +1210,14 @@ class CORE_EXPORT QgsProject : public QObject, public QgsExpressionContextGenera
      */
     void metadataChanged();
 
+    /**
+     * Emitted whenever the project's color scheme has been changed.
+
+     * \see setProjectColors()
+     * \since QGIS 3.6
+     */
+    void projectColorsChanged();
+
     //
     // signals from QgsMapLayerRegistry
     //

tests/src/python/test_qgsproject.py

@@ -27,12 +27,14 @@
                        QgsVectorLayer,
                        QgsRasterLayer,
                        QgsMapLayer,
-                       QgsExpressionContextUtils)
+                       QgsExpressionContextUtils,
+                       QgsProjectColorScheme)
 from qgis.gui import (QgsLayerTreeMapCanvasBridge,
                       QgsMapCanvas)
 
 from qgis.PyQt.QtTest import QSignalSpy
 from qgis.PyQt.QtCore import QT_VERSION_STR, QTemporaryDir
+from qgis.PyQt.QtGui import QColor
 from qgis.PyQt import sip
 
 from qgis.testing import start_app, unittest
@@ -1169,6 +1171,18 @@ def testDirtying(self):
         project.setCrs(QgsCoordinateReferenceSystem('EPSG:3148'))
         self.assertFalse(project.isDirty())
 
+    def testColorScheme(self):
+        p = QgsProject.instance()
+        spy = QSignalSpy(p.projectColorsChanged)
+        p.setProjectColors([[QColor(255, 0, 0), 'red'], [QColor(0, 255, 0), 'green']])
+        self.assertEqual(len(spy), 1)
+        scheme = [s for s in QgsApplication.colorSchemeRegistry().schemes() if isinstance(s, QgsProjectColorScheme)][0]
+        self.assertEqual([[c[0].name(), c[1]] for c in scheme.fetchColors()], [['#ff0000', 'red'], ['#00ff00', 'green']])
+        # except color changed signal when clearing project
+        p.clear()
+        self.assertEqual(len(spy), 2)
+        self.assertEqual([[c[0].name(), c[1]] for c in scheme.fetchColors()], [])
+
 
 if __name__ == '__main__':
     unittest.main()