fixes scala#97

Author: Sciss

src/test/scala/scala/swing/Issue97.scala

@@ -0,0 +1,64 @@
+package scala.swing
+
+import java.util.concurrent.TimeUnit
+
+import org.scalatest.{FlatSpec, Matchers}
+
+import scala.concurrent.duration.Duration
+import scala.concurrent.{Await, Future, Promise}
+import scala.swing.event.{UIElementHidden, UIElementMoved, UIElementResized, UIElementShown}
+import scala.util.control.NonFatal
+
+// Note: `AsyncFlatSpec` has issues with swallowing errors and returning early.
+class Issue97 extends FlatSpec with Matchers {
+  case class Count(shown: Int = 0, hidden: Int = 0, moved: Int = 0, resized: Int = 0)
+
+  def countEvents(): Future[Count] = {
+    val p = Promise[Count]()
+
+    def safely(thunk: => Unit): Unit =
+      try {
+        thunk
+      } catch {
+        case NonFatal(ex) =>
+          p.tryFailure(ex)
+      }
+
+    Swing.onEDT {
+      safely {
+        var c = Count()
+        val lb = new Label("Foo")
+        lb.listenTo(lb)
+        lb.reactions += {
+          case UIElementShown   (`lb`) => c = c.copy(shown    = c.shown   + 1)
+          case UIElementHidden  (`lb`) => c = c.copy(hidden   = c.hidden  + 1)
+          case UIElementMoved   (`lb`) => c = c.copy(moved    = c.moved   + 1)
+          case UIElementResized (`lb`) => c = c.copy(resized  = c.resized + 1)
+        }
+        val b = new BoxPanel(Orientation.Horizontal)
+        b.contents += lb
+        lb.visible = false
+        lb.visible = true
+        b.contents.insert(0, new Label("Bar"))  // about to move `lb` to the right
+        b.peer.doLayout()
+        // note: `Frame#pack()` creates a native window peer,
+        // and thus is not possible to run on Travis without X11
+
+        // wait till next EDT cycle
+        Swing.onEDT {
+          p.trySuccess(c)
+        }
+      }
+    }
+    p.future
+  }
+
+  "Components" should "fire exactly one event when moved, removed or made visible or invisible" in {
+    val futCount = countEvents()
+    val c = Await.result(futCount, Duration(20, TimeUnit.SECONDS))
+    assert(c.shown    === 1)
+    assert(c.hidden   === 1)
+    assert(c.moved    === 1)
+    assert(c.resized  === 1)
+  }
+}