diff --git a/doc/api_break.dox b/doc/api_break.dox
index 190f1b947fc..ce1a1aad4d0 100644
--- a/doc/api_break.dox
+++ b/doc/api_break.dox
@@ -842,6 +842,18 @@ QgsFeatureRendererV2        {#qgis_api_break_3_0_QgsFeatureRendererV2}
 - copyPaintEffect() was removed. copyRendererData() should be used instead.
 
 
+QgsFieldCombobox        {#qgis_api_break_3_0_QgsFieldCombobox}
+----------------
+
+- The setLayer( QgsVectorlayer* ) slot has been removed. Use the setLayer( QgsMapLayer* ) slot instead.
+
+
+QgsFieldExpressionWidget        {#qgis_api_break_3_0_QgsFieldExpressionWidget}
+------------------------
+
+- The setLayer( QgsVectorlayer* ) slot has been removed. Use the setLayer( QgsMapLayer* ) slot instead.
+
+
 QgsFields        {#qgis_api_break_3_0_QgsFields}
 ---------
 
diff --git a/python/gui/qgsfieldcombobox.sip b/python/gui/qgsfieldcombobox.sip
index 57c26f089fb..195168a6a16 100644
--- a/python/gui/qgsfieldcombobox.sip
+++ b/python/gui/qgsfieldcombobox.sip
@@ -42,7 +42,10 @@ class QgsFieldComboBox : QComboBox
     //! return the currently selected field
     QString currentField() const;
 
-    //! Returns the currently used layer
+    /**
+     * Returns the layer currently associated with the combobox.
+     * @see setLayer()
+     */
     QgsVectorLayer* layer() const;
 
   signals:
@@ -50,10 +53,12 @@ class QgsFieldComboBox : QComboBox
     void fieldChanged( const QString& fieldName );
 
   public slots:
-    //! set the layer of which the fields are listed
-    void setLayer( QgsVectorLayer* layer );
 
-    //! convenience slot to connect QgsMapLayerComboBox layer signal
+    /**
+     * Sets the layer for which fields are listed in the combobox. If no layer is set
+     * or a non-vector layer is set then the combobox will be empty.
+     * @see layer()
+     */
     void setLayer( QgsMapLayer* layer );
 
     //! setField sets the currently selected field
diff --git a/python/gui/qgsfieldexpressionwidget.sip b/python/gui/qgsfieldexpressionwidget.sip
index 7b9f1fdc8dd..4c2f92cb266 100644
--- a/python/gui/qgsfieldexpressionwidget.sip
+++ b/python/gui/qgsfieldexpressionwidget.sip
@@ -64,7 +64,10 @@ class QgsFieldExpressionWidget : QWidget
      */
     QString expression() const;
 
-    //! Returns the currently used layer
+    /**
+     * Returns the layer currently associated with the widget.
+     * @see setLayer()
+     */
     QgsVectorLayer* layer() const;
 
     /**
@@ -86,10 +89,10 @@ class QgsFieldExpressionWidget : QWidget
 //    void returnPressed();
 
   public slots:
-    //! set the layer used to display the fields and expression
-    void setLayer( QgsVectorLayer* layer );
-
-    //! convenience slot to connect QgsMapLayerComboBox layer signal
+    /**
+     * Sets the layer used to display the fields and expression.
+     * @see layer()
+     */
     void setLayer( QgsMapLayer* layer );
 
     //! sets the current row in the widget
diff --git a/src/app/composer/qgsatlascompositionwidget.cpp b/src/app/composer/qgsatlascompositionwidget.cpp
index 4b0a9509169..445429484ee 100644
--- a/src/app/composer/qgsatlascompositionwidget.cpp
+++ b/src/app/composer/qgsatlascompositionwidget.cpp
@@ -33,8 +33,8 @@ QgsAtlasCompositionWidget::QgsAtlasCompositionWidget( QWidget* parent, QgsCompos
 
   mAtlasCoverageLayerComboBox->setFilters( QgsMapLayerProxyModel::VectorLayer );
 
-  connect( mAtlasCoverageLayerComboBox, SIGNAL( layerChanged( QgsMapLayer* ) ), mAtlasSortFeatureKeyComboBox, SLOT( setLayer( QgsMapLayer* ) ) );
-  connect( mAtlasCoverageLayerComboBox, SIGNAL( layerChanged( QgsMapLayer* ) ), mPageNameWidget, SLOT( setLayer( QgsMapLayer* ) ) );
+  connect( mAtlasCoverageLayerComboBox, &QgsMapLayerComboBox::layerChanged, mAtlasSortFeatureKeyComboBox, &QgsFieldComboBox::setLayer );
+  connect( mAtlasCoverageLayerComboBox, &QgsMapLayerComboBox::layerChanged, mPageNameWidget, &QgsFieldExpressionWidget::setLayer );
   connect( mAtlasCoverageLayerComboBox, SIGNAL( layerChanged( QgsMapLayer* ) ), this, SLOT( changeCoverageLayer( QgsMapLayer* ) ) );
   connect( mAtlasSortFeatureKeyComboBox, SIGNAL( fieldChanged( QString ) ), this, SLOT( changesSortFeatureField( QString ) ) );
   connect( mPageNameWidget, SIGNAL( fieldChanged( QString, bool ) ), this, SLOT( pageNameExpressionChanged( QString, bool ) ) );
diff --git a/src/app/qgsjoindialog.cpp b/src/app/qgsjoindialog.cpp
index 7c9e5ffb47b..4c52f3a4778 100644
--- a/src/app/qgsjoindialog.cpp
+++ b/src/app/qgsjoindialog.cpp
@@ -43,8 +43,8 @@ QgsJoinDialog::QgsJoinDialog( QgsVectorLayer* layer, QList<QgsMapLayer*> already
 
   mJoinLayerComboBox->setFilters( QgsMapLayerProxyModel::VectorLayer );
   mJoinLayerComboBox->setExceptedLayerList( alreadyJoinedLayers );
-  connect( mJoinLayerComboBox, SIGNAL( layerChanged( QgsMapLayer* ) ), mJoinFieldComboBox, SLOT( setLayer( QgsMapLayer* ) ) );
-  connect( mJoinLayerComboBox, SIGNAL( layerChanged( QgsMapLayer* ) ), this, SLOT( joinedLayerChanged( QgsMapLayer* ) ) );
+  connect( mJoinLayerComboBox, &QgsMapLayerComboBox::layerChanged, mJoinFieldComboBox, &QgsFieldComboBox::setLayer );
+  connect( mJoinLayerComboBox, &QgsMapLayerComboBox::layerChanged, this, &QgsJoinDialog::joinedLayerChanged );
 
   mCacheInMemoryCheckBox->setChecked( true );
 
@@ -55,7 +55,7 @@ QgsJoinDialog::QgsJoinDialog( QgsVectorLayer* layer, QList<QgsMapLayer*> already
     joinedLayerChanged( joinLayer );
   }
 
-  connect( mJoinLayerComboBox, SIGNAL( layerChanged( QgsMapLayer* ) ), this, SLOT( checkDefinitionValid() ) );
+  connect( mJoinLayerComboBox, &QgsMapLayerComboBox::layerChanged, this, &QgsJoinDialog::checkDefinitionValid );
   connect( mJoinFieldComboBox, SIGNAL( fieldChanged( QString ) ), this, SLOT( checkDefinitionValid() ) );
   connect( mTargetFieldComboBox, SIGNAL( fieldChanged( QString ) ), this, SLOT( checkDefinitionValid() ) );
 
diff --git a/src/app/qgslayerstylingwidget.cpp b/src/app/qgslayerstylingwidget.cpp
index c868bd051d0..fc59a6903cb 100644
--- a/src/app/qgslayerstylingwidget.cpp
+++ b/src/app/qgslayerstylingwidget.cpp
@@ -83,7 +83,7 @@ QgsLayerStylingWidget::QgsLayerStylingWidget( QgsMapCanvas* canvas, const QList<
 
   connect( mOptionsListWidget, SIGNAL( currentRowChanged( int ) ), this, SLOT( updateCurrentWidgetLayer() ) );
   connect( mButtonBox->button( QDialogButtonBox::Apply ), SIGNAL( clicked() ), this, SLOT( apply() ) );
-  connect( mLayerCombo, SIGNAL( layerChanged( QgsMapLayer* ) ), this, SLOT( setLayer( QgsMapLayer* ) ) );
+  connect( mLayerCombo, &QgsMapLayerComboBox::layerChanged, this, &QgsLayerStylingWidget::setLayer );
   connect( mLiveApplyCheck, SIGNAL( toggled( bool ) ), this, SLOT( liveApplyToggled( bool ) ) );
 
   mStackedWidget->setCurrentIndex( 0 );
diff --git a/src/app/qgsrelationadddlg.cpp b/src/app/qgsrelationadddlg.cpp
index 3b44e497393..aca91bc24e1 100644
--- a/src/app/qgsrelationadddlg.cpp
+++ b/src/app/qgsrelationadddlg.cpp
@@ -25,10 +25,8 @@ QgsRelationAddDlg::QgsRelationAddDlg( QWidget *parent )
 {
   setupUi( this );
 
-  connect( mCbxReferencingLayer, &QgsMapLayerComboBox::layerChanged, this, [=]( QgsMapLayer * layer ) { mCbxReferencingField->setLayer( layer ); }
-         );
-  connect( mCbxReferencedLayer, &QgsMapLayerComboBox::layerChanged, this, [=]( QgsMapLayer * layer ) { mCbxReferencedField->setLayer( layer ); }
-         );
+  connect( mCbxReferencingLayer, &QgsMapLayerComboBox::layerChanged, mCbxReferencingField, &QgsFieldComboBox::setLayer );
+  connect( mCbxReferencedLayer, &QgsMapLayerComboBox::layerChanged, mCbxReferencedField, &QgsFieldComboBox::setLayer );
 
   mCbxReferencingLayer->setFilters( QgsMapLayerProxyModel::VectorLayer );
   mCbxReferencingField->setLayer( mCbxReferencingLayer->currentLayer() );
diff --git a/src/gui/editorwidgets/qgsvaluerelationconfigdlg.cpp b/src/gui/editorwidgets/qgsvaluerelationconfigdlg.cpp
index 7bbe41d0a32..a32d5dc6151 100644
--- a/src/gui/editorwidgets/qgsvaluerelationconfigdlg.cpp
+++ b/src/gui/editorwidgets/qgsvaluerelationconfigdlg.cpp
@@ -23,8 +23,8 @@ QgsValueRelationConfigDlg::QgsValueRelationConfigDlg( QgsVectorLayer* vl, int fi
 {
   setupUi( this );
   mLayerName->setFilters( QgsMapLayerProxyModel::VectorLayer );
-  connect( mLayerName, SIGNAL( layerChanged( QgsMapLayer* ) ), mKeyColumn, SLOT( setLayer( QgsMapLayer* ) ) );
-  connect( mLayerName, SIGNAL( layerChanged( QgsMapLayer* ) ), mValueColumn, SLOT( setLayer( QgsMapLayer* ) ) );
+  connect( mLayerName, &QgsMapLayerComboBox::layerChanged, mKeyColumn, &QgsFieldComboBox::setLayer );
+  connect( mLayerName, &QgsMapLayerComboBox::layerChanged, mValueColumn, &QgsFieldComboBox::setLayer );
   connect( mEditExpression, SIGNAL( clicked() ), this, SLOT( editExpression() ) );
 
   connect( mLayerName, SIGNAL( layerChanged( QgsMapLayer* ) ), this, SIGNAL( changed() ) );
diff --git a/src/gui/qgsfieldcombobox.cpp b/src/gui/qgsfieldcombobox.cpp
index 79f635f54c1..675dd23fc87 100644
--- a/src/gui/qgsfieldcombobox.cpp
+++ b/src/gui/qgsfieldcombobox.cpp
@@ -45,16 +45,8 @@ bool QgsFieldComboBox::allowEmptyFieldName() const
 
 void QgsFieldComboBox::setLayer( QgsMapLayer *layer )
 {
-  QgsVectorLayer* vl = dynamic_cast<QgsVectorLayer*>( layer );
-  if ( vl )
-  {
-    setLayer( vl );
-  }
-}
-
-void QgsFieldComboBox::setLayer( QgsVectorLayer *layer )
-{
-  mFieldProxyModel->sourceFieldModel()->setLayer( layer );
+  QgsVectorLayer* vl = qobject_cast<QgsVectorLayer*>( layer );
+  mFieldProxyModel->sourceFieldModel()->setLayer( vl );
 }
 
 QgsVectorLayer *QgsFieldComboBox::layer() const
diff --git a/src/gui/qgsfieldcombobox.h b/src/gui/qgsfieldcombobox.h
index 804309116ce..0b25395236c 100644
--- a/src/gui/qgsfieldcombobox.h
+++ b/src/gui/qgsfieldcombobox.h
@@ -68,7 +68,10 @@ class GUI_EXPORT QgsFieldComboBox : public QComboBox
     //! return the currently selected field
     QString currentField() const;
 
-    //! Returns the currently used layer
+    /**
+     * Returns the layer currently associated with the combobox.
+     * @see setLayer()
+     */
     QgsVectorLayer* layer() const;
 
   signals:
@@ -76,10 +79,12 @@ class GUI_EXPORT QgsFieldComboBox : public QComboBox
     void fieldChanged( const QString& fieldName );
 
   public slots:
-    //! set the layer of which the fields are listed
-    void setLayer( QgsVectorLayer* layer );
 
-    //! convenience slot to connect QgsMapLayerComboBox layer signal
+    /**
+     * Sets the layer for which fields are listed in the combobox. If no layer is set
+     * or a non-vector layer is set then the combobox will be empty.
+     * @see layer()
+     */
     void setLayer( QgsMapLayer* layer );
 
     //! setField sets the currently selected field
diff --git a/src/gui/qgsfieldexpressionwidget.cpp b/src/gui/qgsfieldexpressionwidget.cpp
index 1984e2fae04..c2aa7e73281 100644
--- a/src/gui/qgsfieldexpressionwidget.cpp
+++ b/src/gui/qgsfieldexpressionwidget.cpp
@@ -154,24 +154,17 @@ void QgsFieldExpressionWidget::registerExpressionContextGenerator( const QgsExpr
 
 void QgsFieldExpressionWidget::setLayer( QgsMapLayer *layer )
 {
-  QgsVectorLayer* vl = dynamic_cast<QgsVectorLayer*>( layer );
-  if ( vl )
-  {
-    setLayer( vl );
-  }
-}
+  QgsVectorLayer* vl = qobject_cast< QgsVectorLayer* >( layer );
 
-void QgsFieldExpressionWidget::setLayer( QgsVectorLayer *layer )
-{
   if ( mFieldProxyModel->sourceFieldModel()->layer() )
     disconnect( mFieldProxyModel->sourceFieldModel()->layer(), SIGNAL( updatedFields() ), this, SLOT( reloadLayer() ) );
 
-  if ( layer )
-    mExpressionContext = layer->createExpressionContext();
+  if ( vl )
+    mExpressionContext = vl->createExpressionContext();
   else
     mExpressionContext = QgsProject::instance()->createExpressionContext();
 
-  mFieldProxyModel->sourceFieldModel()->setLayer( layer );
+  mFieldProxyModel->sourceFieldModel()->setLayer( vl );
 
   if ( mFieldProxyModel->sourceFieldModel()->layer() )
     connect( mFieldProxyModel->sourceFieldModel()->layer(), SIGNAL( updatedFields() ), SLOT( reloadLayer() ), Qt::UniqueConnection );
diff --git a/src/gui/qgsfieldexpressionwidget.h b/src/gui/qgsfieldexpressionwidget.h
index e7afdb43e40..480fa6e4a32 100644
--- a/src/gui/qgsfieldexpressionwidget.h
+++ b/src/gui/qgsfieldexpressionwidget.h
@@ -111,7 +111,10 @@ class GUI_EXPORT QgsFieldExpressionWidget : public QWidget
      */
     QString expression() const;
 
-    //! Returns the currently used layer
+    /**
+     * Returns the layer currently associated with the widget.
+     * @see setLayer()
+     */
     QgsVectorLayer* layer() const;
 
     /**
@@ -133,10 +136,11 @@ class GUI_EXPORT QgsFieldExpressionWidget : public QWidget
 //    void returnPressed();
 
   public slots:
-    //! set the layer used to display the fields and expression
-    void setLayer( QgsVectorLayer* layer );
 
-    //! convenience slot to connect QgsMapLayerComboBox layer signal
+    /**
+     * Sets the layer used to display the fields and expression.
+     * @see layer()
+     */
     void setLayer( QgsMapLayer* layer );
 
     //! sets the current row in the widget
diff --git a/src/gui/qgsorderbydialog.cpp b/src/gui/qgsorderbydialog.cpp
index 7c6b78cfaaf..330baef6c2c 100644
--- a/src/gui/qgsorderbydialog.cpp
+++ b/src/gui/qgsorderbydialog.cpp
@@ -18,6 +18,7 @@
 
 #include "qgsexpressionbuilderdialog.h"
 #include "qgsfieldexpressionwidget.h"
+#include "qgsvectorlayer.h"
 
 #include <QTableWidget>
 #include <QKeyEvent>
diff --git a/src/plugins/heatmap/heatmapgui.cpp b/src/plugins/heatmap/heatmapgui.cpp
index 99a5e55e1b7..db72ff97cf0 100644
--- a/src/plugins/heatmap/heatmapgui.cpp
+++ b/src/plugins/heatmap/heatmapgui.cpp
@@ -71,8 +71,8 @@ HeatmapGui::HeatmapGui( QWidget* parent, Qt::WindowFlags fl, QMap<QString, QVari
 
   mRadiusFieldCombo->setFilters( QgsFieldProxyModel::Numeric );
   mWeightFieldCombo->setFilters( QgsFieldProxyModel::Numeric );
-  connect( mInputLayerCombo, SIGNAL( layerChanged( QgsMapLayer* ) ), mRadiusFieldCombo, SLOT( setLayer( QgsMapLayer* ) ) );
-  connect( mInputLayerCombo, SIGNAL( layerChanged( QgsMapLayer* ) ), mWeightFieldCombo, SLOT( setLayer( QgsMapLayer* ) ) );
+  connect( mInputLayerCombo, &QgsMapLayerComboBox::layerChanged, mRadiusFieldCombo, &QgsFieldComboBox::setLayer );
+  connect( mInputLayerCombo, &QgsMapLayerComboBox::layerChanged, mWeightFieldCombo, &QgsFieldComboBox::setLayer );
   mRadiusFieldCombo->setLayer( mInputLayerCombo->currentLayer() );
   mWeightFieldCombo->setLayer( mInputLayerCombo->currentLayer() );