[needs-docs] Allow dragging project layers from legend over map layer comboboxes to select

nyalldawson · nyalldawson · commit cf63a7af973b · 2019-06-13T04:57:37.000+10:00
Greatly assists with usability of the combobox with large projects,
especially those with multiple copies of layers with the same name...
diff --git a/python/gui/auto_generated/qgsmaplayercombobox.sip.in b/python/gui/auto_generated/qgsmaplayercombobox.sip.in
@@ -154,6 +154,17 @@ setLayer set the current layer selected in the combo
 Emitted whenever the currently selected layer changes.
 %End
 
+  protected:
+
+    virtual void dragEnterEvent( QDragEnterEvent *event );
+
+    virtual void dragLeaveEvent( QDragLeaveEvent *event );
+
+    virtual void dropEvent( QDropEvent *event );
+
+    virtual void paintEvent( QPaintEvent *e );
+
+
   protected slots:
     void indexChanged( int i );
     void rowsChanged();
diff --git a/src/gui/qgsmaplayercombobox.cpp b/src/gui/qgsmaplayercombobox.cpp
@@ -15,7 +15,9 @@
 
 #include "qgsmaplayercombobox.h"
 #include "qgsmaplayermodel.h"
-
+#include "qgsmimedatautils.h"
+#include <QDragEnterEvent>
+#include <QPainter>
 
 QgsMapLayerComboBox::QgsMapLayerComboBox( QWidget *parent )
   : QComboBox( parent )
@@ -26,6 +28,8 @@ QgsMapLayerComboBox::QgsMapLayerComboBox( QWidget *parent )
   connect( this, static_cast < void ( QComboBox::* )( int ) > ( &QComboBox::activated ), this, &QgsMapLayerComboBox::indexChanged );
   connect( mProxyModel, &QAbstractItemModel::rowsInserted, this, &QgsMapLayerComboBox::rowsChanged );
   connect( mProxyModel, &QAbstractItemModel::rowsRemoved, this, &QgsMapLayerComboBox::rowsChanged );
+
+  setAcceptDrops( true );
 }
 
 void QgsMapLayerComboBox::setExcludedProviders( const QStringList &providers )
@@ -138,3 +142,74 @@ void QgsMapLayerComboBox::rowsChanged()
   }
 }
 
+QgsMapLayer *QgsMapLayerComboBox::compatibleMapLayerFromMimeData( const QMimeData *data ) const
+{
+  const QgsMimeDataUtils::UriList uriList = QgsMimeDataUtils::decodeUriList( data );
+  for ( const QgsMimeDataUtils::Uri &u : uriList )
+  {
+    // is this uri from the current project?
+    if ( QgsMapLayer *layer = u.mapLayer() )
+    {
+      if ( mProxyModel->acceptsLayer( layer ) )
+        return layer;
+    }
+  }
+  return nullptr;
+}
+
+void QgsMapLayerComboBox::dragEnterEvent( QDragEnterEvent *event )
+{
+  if ( !( event->possibleActions() & Qt::CopyAction ) )
+    return;
+
+  if ( compatibleMapLayerFromMimeData( event->mimeData() ) )
+  {
+    // dragged an acceptable layer, phew
+    event->setDropAction( Qt::CopyAction );
+    event->accept();
+    mDragActive = true;
+    update();
+  }
+}
+
+void QgsMapLayerComboBox::dragLeaveEvent( QDragLeaveEvent *event )
+{
+  QComboBox::dragLeaveEvent( event );
+  if ( mDragActive )
+  {
+    event->accept();
+    mDragActive = false;
+    update();
+  }
+}
+
+void QgsMapLayerComboBox::dropEvent( QDropEvent *event )
+{
+  if ( !( event->possibleActions() & Qt::CopyAction ) )
+    return;
+
+  if ( QgsMapLayer *layer = compatibleMapLayerFromMimeData( event->mimeData() ) )
+  {
+    // dropped an acceptable layer, phew
+    setFocus( Qt::MouseFocusReason );
+    event->setDropAction( Qt::CopyAction );
+    event->accept();
+
+    setLayer( layer );
+  }
+  mDragActive = false;
+  update();
+}
+
+void QgsMapLayerComboBox::paintEvent( QPaintEvent *e )
+{
+  QComboBox::paintEvent( e );
+  if ( mDragActive )
+  {
+    QPainter p( this );
+    int width = 2;  // width of highlight rectangle inside frame
+    p.setPen( QPen( palette().highlight(), width ) );
+    QRect r = rect().adjusted( width, width, -width, -width );
+    p.drawRect( r );
+  }
+}
diff --git a/src/gui/qgsmaplayercombobox.h b/src/gui/qgsmaplayercombobox.h
@@ -139,12 +139,26 @@ class GUI_EXPORT QgsMapLayerComboBox : public QComboBox
     //! Emitted whenever the currently selected layer changes.
     void layerChanged( QgsMapLayer *layer );
 
+  protected:
+
+    void dragEnterEvent( QDragEnterEvent *event ) override;
+    void dragLeaveEvent( QDragLeaveEvent *event ) override;
+    void dropEvent( QDropEvent *event ) override;
+    void paintEvent( QPaintEvent *e ) override;
+
   protected slots:
     void indexChanged( int i );
     void rowsChanged();
 
   private:
     QgsMapLayerProxyModel *mProxyModel = nullptr;
+    bool mDragActive = false;
+
+    /**
+     * Returns a map layer, compatible with the filters set for the combo box, from
+     * the specified mime \a data (if possible!).
+     */
+    QgsMapLayer *compatibleMapLayerFromMimeData( const QMimeData *data ) const;
 };
 
 #endif // QGSMAPLAYERCOMBOBOX_H
