Allow QgsCustomDropHandlers to directly operate mime data

and dropped file names

This allows QgsCustomDropHandlers which aren't directly associated
with providers (e.g. for plugins to handle dropped files of
a certain type)

python/gui/qgscustomdrophandler.sip

@@ -14,6 +14,11 @@ class QgsCustomDropHandler
  Abstract base class that may be implemented to handle new types of data to be dropped in QGIS.
  Implementations will be used when a QgsMimeDataUtils.Uri has layerType equal to "custom",
  and the providerKey is equal to key() returned by the implementation.
+
+ Alternatively, implementations can override the handleMimeData() or handleFileDrop()
+ methods to handle QMimeData and file drops directly. Reimplementation of these methods
+ does not rely on key() matching.
+
 .. versionadded:: 3.0
 %End
 
@@ -29,9 +34,39 @@ Type of custom URI recognized by the handler
  :rtype: str
 %End
 
-    virtual void handleDrop( const QgsMimeDataUtils::Uri &uri ) const = 0;
+    virtual void handleDrop( const QgsMimeDataUtils::Uri &uri ) const;
 %Docstring
 Method called from QGIS after a drop event with custom URI known by the handler
+%End
+
+    virtual void handleMimeData( const QMimeData *data );
+%Docstring
+ Called when the specified mime ``data`` has been dropped onto QGIS.
+
+ The base class implementation does nothing.
+
+ Subclasses should take care when overriding this method. When a drop event
+ occurs, Qt will lock the source application of the drag for the duration
+ of the drop event handling (e.g. dragging files from explorer to QGIS will
+ lock the explorer window until the drop handling has been complete).
+
+ Accordingly, only implementations must be lightweight and return ASAP.
+ (For instance by copying the relevant parts of ``data`` and then handling
+ the data after a short timeout).
+%End
+
+    virtual bool handleFileDrop( const QString &file );
+%Docstring
+ Called when the specified ``file`` has been dropped onto QGIS. If true
+ is returned, then the handler has accepted this file and it should not
+ be further processed (e.g. by other QgsCustomDropHandlers).
+
+ The base class implementation does nothing.
+
+ This method is not called directly while drop handling is occurring,
+ so the limitations described in handleMimeData() about returning
+ quickly do not apply.
+ :rtype: bool
 %End
 };
 

src/app/qgisapp.cpp

@@ -1333,6 +1333,13 @@ void QgisApp::dropEvent( QDropEvent *event )
   timer->setSingleShot( true );
   timer->setInterval( 50 );
 
+  // first, allow custom handlers to directly operate on the mime data
+  const QList<QgsCustomDropHandler *> handlers = mCustomDropHandlers;
+  for ( QgsCustomDropHandler *handler : handlers )
+  {
+    handler->handleMimeData( event->mimeData() );
+  }
+
   // get the file list
   QList<QUrl>::iterator i;
   QList<QUrl>urls = event->mimeData()->urls();
@@ -1405,7 +1412,21 @@ void QgisApp::dropEvent( QDropEvent *event )
 
     for ( const QString &file : qgsAsConst( files ) )
     {
-      openFile( file );
+      bool handled = false;
+
+      // give custom drop handlers first priority at handling the file
+      const QList<QgsCustomDropHandler *> handlers = mCustomDropHandlers;
+      for ( QgsCustomDropHandler *handler : handlers )
+      {
+        if ( handler->handleFileDrop( file ) )
+        {
+          handled = true;
+          break;
+        }
+      }
+
+      if ( !handled )
+        openFile( file );
     }
 
     if ( !lst.isEmpty() )

src/gui/qgscustomdrophandler.cpp

@@ -14,3 +14,19 @@
  ***************************************************************************/
 
 #include "qgscustomdrophandler.h"
+
+void QgsCustomDropHandler::handleDrop( const QgsMimeDataUtils::Uri &uri ) const
+{
+  Q_UNUSED( uri );
+}
+
+void QgsCustomDropHandler::handleMimeData( const QMimeData *data )
+{
+  Q_UNUSED( data );
+}
+
+bool QgsCustomDropHandler::handleFileDrop( const QString &file )
+{
+  Q_UNUSED( file );
+  return false;
+}

src/gui/qgscustomdrophandler.h

@@ -23,6 +23,11 @@
  * Abstract base class that may be implemented to handle new types of data to be dropped in QGIS.
  * Implementations will be used when a QgsMimeDataUtils::Uri has layerType equal to "custom",
  * and the providerKey is equal to key() returned by the implementation.
+ *
+ * Alternatively, implementations can override the handleMimeData() or handleFileDrop()
+ * methods to handle QMimeData and file drops directly. Reimplementation of these methods
+ * does not rely on key() matching.
+ *
  * \since QGIS 3.0
  */
 class GUI_EXPORT QgsCustomDropHandler
@@ -34,7 +39,36 @@ class GUI_EXPORT QgsCustomDropHandler
     virtual QString key() const = 0;
 
     //! Method called from QGIS after a drop event with custom URI known by the handler
-    virtual void handleDrop( const QgsMimeDataUtils::Uri &uri ) const = 0;
+    virtual void handleDrop( const QgsMimeDataUtils::Uri &uri ) const;
+
+    /**
+     * Called when the specified mime \a data has been dropped onto QGIS.
+     *
+     * The base class implementation does nothing.
+     *
+     * Subclasses should take care when overriding this method. When a drop event
+     * occurs, Qt will lock the source application of the drag for the duration
+     * of the drop event handling (e.g. dragging files from explorer to QGIS will
+     * lock the explorer window until the drop handling has been complete).
+     *
+     * Accordingly, only implementations must be lightweight and return ASAP.
+     * (For instance by copying the relevant parts of \a data and then handling
+     * the data after a short timeout).
+     */
+    virtual void handleMimeData( const QMimeData *data );
+
+    /**
+     * Called when the specified \a file has been dropped onto QGIS. If true
+     * is returned, then the handler has accepted this file and it should not
+     * be further processed (e.g. by other QgsCustomDropHandlers).
+     *
+     * The base class implementation does nothing.
+     *
+     * This method is not called directly while drop handling is occurring,
+     * so the limitations described in handleMimeData() about returning
+     * quickly do not apply.
+     */
+    virtual bool handleFileDrop( const QString &file );
 };
 
 #endif // QGSCUSTOMDROPHANDLER_H