Fix for #2980. No review.

2 files changed, 12 insertions, 3 deletions

diff --git a/src/swing/scala/swing/BorderPanel.scala b/src/swing/scala/swing/BorderPanel.scala
index 2acc56787b..01fe873f93 100644
--- a/src/swing/scala/swing/BorderPanel.scala
+++ b/src/swing/scala/swing/BorderPanel.scala
@@ -51,5 +51,11 @@ class BorderPanel extends Panel with LayoutContainer {
     wrapPosition(layoutManager.getConstraints(comp.peer).asInstanceOf[String])
 
   protected def areValid(c: Constraints): (Boolean, String) = (true, "")
-  protected def add(c: Component, l: Constraints) { peer.add(c.peer, l.toString) }
+  protected def add(c: Component, l: Constraints) {
+    // we need to remove previous components with the same constraints as the new one,
+    // otherwise the layout manager loses track of the old one
+    val old = layoutManager.getLayoutComponent(l.toString)
+    if(old != null) peer.remove(old)
+    peer.add(c.peer, l.toString)
+  }
 }
diff --git a/src/swing/scala/swing/LayoutContainer.scala b/src/swing/scala/swing/LayoutContainer.scala
index b58064ed07..8e94bf565f 100644
--- a/src/swing/scala/swing/LayoutContainer.scala
+++ b/src/swing/scala/swing/LayoutContainer.scala
@@ -42,7 +42,10 @@ trait LayoutContainer extends Container.Wrapper {
   protected def areValid(c: Constraints): (Boolean, String)
   /**
    * Adds a component with the given constraints to the underlying layout
-   * manager and the component peer.
+   * manager and the component peer. This method needs to interact properly
+   * with method `constraintsFor`, i.e., it might need to remove previously
+   * held components in order to maintain layout consistency. See `BorderPanel`
+   * for an example.
    */
   protected def add(comp: Component, c: Constraints)
 
@@ -53,7 +56,7 @@ trait LayoutContainer extends Container.Wrapper {
    *
    * layout(myComponent) = myConstraints
    *
-   * also ensures that myComponent is properly add to this container.
+   * also ensures that myComponent is properly added to this container.
    */
   def layout: Map[Component, Constraints] = new Map[Component, Constraints] {
     def -= (c: Component): this.type = { _contents -= c; this }