transplant of sceneEventFilter and mouseMoveEvent from the icon applet to the applet class, this will cause a lot less duplication.

if you want to make a widget draggable around just call the new function
  void watchForMouseMove(QGraphicsItem * watched, bool watch)

also, some style fixes.

svn path=/trunk/KDE/kdebase/workspace/libs/plasma/; revision=777705

applet.cpp

@@ -33,6 +33,7 @@
 #include <QTextDocument>
 #include <QTimer>
 #include <QUiLoader>
+#include <QGraphicsSceneMouseEvent>
 
 #include <KIcon>
 #include <KColorScheme>
@@ -284,6 +285,7 @@ public:
     KPluginInfo appletDescription;
     Package* package;
     QList<QObject*> watchedForFocus;
+    QList<QGraphicsItem*> watchedForMouseMove;
     QStringList loadedEngines;
     Plasma::SvgPanel *background;
     Plasma::LineEdit *failureText;
@@ -1120,6 +1122,24 @@ void Applet::watchForFocus(QObject *widget, bool watch)
     }
 }
 
+void Applet::watchForMouseMove( QGraphicsItem * watched, bool watch )
+{
+    if (!watched) {
+        return;
+    }
+
+    int index = d->watchedForMouseMove.indexOf(watched);
+    if (watch) {
+        if (index == -1) {
+            d->watchedForMouseMove.append(watched);
+            watched->installSceneEventFilter(this);
+        }
+    } else if (index != -1) {
+        d->watchedForMouseMove.removeAt(index);
+        watched->removeSceneEventFilter(this);
+    }
+}
+
 void Applet::needsFocus(bool focus)
 {
     if (focus == QGraphicsItem::hasFocus()) {
@@ -1154,6 +1174,51 @@ bool Applet::eventFilter( QObject *o, QEvent * e )
     return QObject::eventFilter(o, e);
 }
 
+bool Applet::sceneEventFilter( QGraphicsItem * watched, QEvent * event )
+{
+    switch (event->type()) {
+        case QEvent::GraphicsSceneMouseMove: {
+            if (d->watchedForMouseMove.contains( watched )) {
+                mouseMoveEvent(static_cast<QGraphicsSceneMouseEvent*>(event));
+                return true;
+            }
+            break;
+        }
+
+        default:
+            break;
+    }
+
+    return QGraphicsItem::sceneEventFilter(watched, event);
+}
+
+void Applet::mouseMoveEvent(QGraphicsSceneMouseEvent *event)
+{
+    if (!isImmutable() && formFactor() == Plasma::Planar) {
+        QGraphicsItem *parent = parentItem();
+        Plasma::Applet *applet = qgraphicsitem_cast<Plasma::Applet*>(parent);
+
+        if (applet && applet->isContainment()) {
+            // our direct parent is a containment. just move ourselves.
+            QPointF curPos = event->pos();
+            QPointF lastPos = event->lastPos();
+            QPointF delta = curPos-lastPos;
+
+            moveBy(delta.x(),delta.y());
+        } else if (parent) {
+            //don't move the icon as well because our parent (usually an appletHandle) will do it for us
+            //parent->moveBy(delta.x(),delta.y());
+            QPointF curPos = parent->transform().map(event->pos());
+            QPointF lastPos = parent->transform().map(event->lastPos());
+            QPointF delta = curPos-lastPos;
+
+            parent->setPos(parent->pos() + delta);
+        }
+
+    }
+}
+
+
 void Applet::showConfigurationInterface()
 {
     if (d->package && d->configXml) {

applet.h

@@ -722,13 +722,25 @@ class PLASMA_EXPORT Applet : public Widget
         /**
         * Register widgets that can receive keyboard focus.
         *
-        * Calling this results in an eventFilter being places on the widget.
+        * Calling this results in an eventFilter being placed on the widget.
         *
         * @param widget the widget to watch for keyboard focus
         * @param watch whether to start watching the widget, or to stop doing so
         */
         void watchForFocus(QObject *widget, bool watch = true);
 
+        /**
+         * Register the widgets that manages mouse clicks but you still want
+         * to be able to drag the applet around when holding the mouse pointer
+         * on that widgets.
+         *
+         * Calling this results in an eventFilter being places on the widget.
+         *
+         * @param widget the widget to watch for mouse move
+         * @param watch whether to start watching the widget, or to stop doing so
+         */
+        void watchForMouseMove(QGraphicsItem * watched, bool watch);
+
         /**
         * Call this whenever focus is needed or not needed.
         *
@@ -745,6 +757,16 @@ class PLASMA_EXPORT Applet : public Widget
          **/
         bool eventFilter( QObject *o, QEvent *e );
 
+        /**
+         * @internal scene event filter; used to manage applet dragging
+         */
+        bool sceneEventFilter ( QGraphicsItem * watched, QEvent * event );
+
+        /**
+         * @internal manage the mouse movement to drag the applet around
+         */
+        void mouseMoveEvent(QGraphicsSceneMouseEvent *event);
+
         /**
          * Reimpmlemented from LayoutItem
          */