Add a "not set" option to QgsRasterBandComboBox

python/gui/raster/qgsrasterbandcombobox.sip

@@ -41,6 +41,21 @@ class QgsRasterBandComboBox : QComboBox
  :rtype: int
 %End
 
+    bool isShowingNotSetOption() const;
+%Docstring
+ Returns true if the combo box is showing the "not set" option.
+.. seealso:: setShowNotSetOption()
+ :rtype: bool
+%End
+
+    void setShowNotSetOption( bool show, const QString &string = QString() );
+%Docstring
+ Sets whether the combo box should show the "not set" option.
+ Optionally the built in "not set" text can be overridden by specifying
+ a ``string``.
+.. seealso:: setShowNotSetOption()
+%End
+
   public slots:
 
     void setLayer( QgsMapLayer *layer );

src/gui/raster/qgsmultibandcolorrendererwidget.cpp

@@ -57,15 +57,13 @@ QgsMultiBandColorRendererWidget::QgsMultiBandColorRendererWidget( QgsRasterLayer
     connect( mBlueBandComboBox, &QgsRasterBandComboBox::bandChanged,
              this, &QgsMultiBandColorRendererWidget::onBandChanged );
 
+    mRedBandComboBox->setShowNotSetOption( true );
+    mGreenBandComboBox->setShowNotSetOption( true );
+    mBlueBandComboBox->setShowNotSetOption( true );
     mRedBandComboBox->setLayer( mRasterLayer );
     mGreenBandComboBox->setLayer( mRasterLayer );
     mBlueBandComboBox->setLayer( mRasterLayer );
 
-    //fill available bands into combo boxes
-    mRedBandComboBox->insertItem( 0, tr( "Not set" ), -1 );
-    mGreenBandComboBox->insertItem( 0, tr( "Not set" ), -1 );
-    mBlueBandComboBox->insertItem( 0, tr( "Not set" ), -1 );
-
     //contrast enhancement algorithms
     mContrastEnhancementAlgorithmComboBox->addItem( tr( "No enhancement" ), QgsContrastEnhancement::NoEnhancement );
     mContrastEnhancementAlgorithmComboBox->addItem( tr( "Stretch to MinMax" ), QgsContrastEnhancement::StretchToMinimumMaximum );

src/gui/raster/qgsrasterbandcombobox.cpp

@@ -19,6 +19,7 @@
 
 QgsRasterBandComboBox::QgsRasterBandComboBox( QWidget *parent )
   : QComboBox( parent )
+  , mNotSetString( tr( "Not set" ) )
 {
   connect( this, static_cast<void ( QComboBox::* )( int )>( &QComboBox::currentIndexChanged ), this, [ = ]
   {
@@ -43,6 +44,9 @@ void QgsRasterBandComboBox::setLayer( QgsMapLayer *layer )
   blockSignals( true );
   clear();
 
+  if ( mShowNotSet )
+    addItem( mNotSetString, -1 );
+
   if ( mLayer )
   {
     QgsRasterDataProvider *provider = mLayer->dataProvider();
@@ -70,6 +74,18 @@ void QgsRasterBandComboBox::setBand( int band )
   setCurrentIndex( findData( band ) );
 }
 
+bool QgsRasterBandComboBox::isShowingNotSetOption() const
+{
+  return mShowNotSet;
+}
+
+void QgsRasterBandComboBox::setShowNotSetOption( bool show, const QString &string )
+{
+  mShowNotSet = show;
+  mNotSetString = string.isEmpty() ? tr( "Not set" ) : string;
+  setLayer( mLayer );
+}
+
 QString QgsRasterBandComboBox::displayBandName( QgsRasterDataProvider *provider, int band ) const
 {
   if ( !provider )

src/gui/raster/qgsrasterbandcombobox.h

@@ -55,6 +55,20 @@ class GUI_EXPORT QgsRasterBandComboBox : public QComboBox
      */
     int currentBand() const;
 
+    /**
+     * Returns true if the combo box is showing the "not set" option.
+     * \see setShowNotSetOption()
+     */
+    bool isShowingNotSetOption() const;
+
+    /**
+     * Sets whether the combo box should show the "not set" option.
+     * Optionally the built in "not set" text can be overridden by specifying
+     * a \a string.
+     * \see setShowNotSetOption()
+     */
+    void setShowNotSetOption( bool show, const QString &string = QString() );
+
   public slots:
 
     /**
@@ -81,6 +95,9 @@ class GUI_EXPORT QgsRasterBandComboBox : public QComboBox
 
     QPointer< QgsRasterLayer > mLayer;
 
+    bool mShowNotSet = false;
+    QString mNotSetString;
+
     QString displayBandName( QgsRasterDataProvider *provider, int band ) const;