Fix for #1442

2 files changed, 29 insertions, 7 deletions

diff --git a/src/swing/scala/swing/Component.scala b/src/swing/scala/swing/Component.scala
index 36600e9e19..4ca5149f87 100644
--- a/src/swing/scala/swing/Component.scala
+++ b/src/swing/scala/swing/Component.scala
@@ -189,12 +189,16 @@ abstract class Component extends UIElement with Publisher {
     /**
      * Publishes mouse wheel moves.
      */
-    val wheel: Publisher = new Publisher {
-      peer.addMouseWheelListener(new MouseWheelListener {
-        def mouseWheelMoved(e: java.awt.event.MouseWheelEvent) {
-          publish(MouseWheelMoved(Component.wrapperFor(e.getSource.asInstanceOf[JComponent]),
-                             e.getPoint, e.getModifiersEx, e.getWheelRotation)(e.getWhen)) }
-      })
+    val wheel: Publisher = new LazyPublisher {
+      // We need to subscribe lazily and unsubscribe, since components in scroll panes capture
+      // mouse wheel events if there is a listener installed. See ticket #1442.
+      lazy val l = new MouseWheelListener {
+          def mouseWheelMoved(e: java.awt.event.MouseWheelEvent) {
+            publish(MouseWheelMoved(Component.wrapperFor(e.getSource.asInstanceOf[JComponent]),
+                e.getPoint, e.getModifiersEx, e.getWheelRotation)(e.getWhen)) }
+        }
+      def onFirstSubscribe() = peer.addMouseWheelListener(l)
+      def onLastUnsubscribe() = peer.removeMouseWheelListener(l)
     }
   }
 
diff --git a/src/swing/scala/swing/Publisher.scala b/src/swing/scala/swing/Publisher.scala
index 67728705a0..1db4ecaced 100644
--- a/src/swing/scala/swing/Publisher.scala
+++ b/src/swing/scala/swing/Publisher.scala
@@ -38,6 +38,24 @@ trait Publisher extends Reactor {
   listenTo(this)
 }
 
+private[swing] trait LazyPublisher extends Publisher {
+  import Reactions._
+
+  def onFirstSubscribe()
+  def onLastUnsubscribe()
+
+  override def subscribe(listener: Reaction) {
+    if(listeners.size == 1) onFirstSubscribe()
+    super.subscribe(listener)
+  }
+  override def unsubscribe(listener: Reaction) {
+    super.unsubscribe(listener)
+    if(listeners.size == 1) onLastUnsubscribe()
+  }
+}
+
+
+
 import scala.ref._
 
 private[swing] trait SingleRefCollection[+A <: AnyRef] extends Collection[A] { self =>
@@ -102,7 +120,7 @@ private[swing] class StrongReference[+T <: AnyRef](value: T) extends Reference[T
     def isEnqueued(): Boolean = false
   }
 
-  abstract class RefBuffer[A <: AnyRef] extends Buffer[A] with SingleRefCollection[A] { self =>
+abstract class RefBuffer[A <: AnyRef] extends Buffer[A] with SingleRefCollection[A] { self =>
   protected val underlying: Buffer[Reference[A]]
 
   def +=(el: A) { purgeReferences(); underlying += Ref(el) }