425926: ensure addScrollListener does not require a scroll bar

Impossible to scroll after patchset lost focus

Change-Id: I9f4315794444dafacc29d75a2dbcb18c17a553f6
Task-Url: https://bugs.eclipse.org/bugs/show_bug.cgi?id=425926

2 files changed, 39 insertions, 19 deletions

diff --git a/org.eclipse.mylyn.tasks.tests/src/org/eclipse/mylyn/tasks/tests/ui/editor/EditorUtilTest.java b/org.eclipse.mylyn.tasks.tests/src/org/eclipse/mylyn/tasks/tests/ui/editor/EditorUtilTest.java
index bcb34975a..a487fa883 100644
--- a/org.eclipse.mylyn.tasks.tests/src/org/eclipse/mylyn/tasks/tests/ui/editor/EditorUtilTest.java
+++ b/org.eclipse.mylyn.tasks.tests/src/org/eclipse/mylyn/tasks/tests/ui/editor/EditorUtilTest.java
@@ -14,9 +14,12 @@ package org.eclipse.mylyn.tasks.tests.ui.editor;
 import junit.framework.TestCase;
 
 import org.eclipse.mylyn.commons.ui.CommonUiUtil;
+import org.eclipse.mylyn.commons.workbench.WorkbenchUtil;
+import org.eclipse.mylyn.internal.tasks.ui.editors.EditorUtil;
 import org.eclipse.swt.SWT;
 import org.eclipse.swt.widgets.Composite;
 import org.eclipse.swt.widgets.Label;
+import org.eclipse.swt.widgets.Scrollable;
 import org.eclipse.swt.widgets.Shell;
 
 /**
@@ -113,4 +116,23 @@ public class EditorUtilTest extends TestCase {
 		assertFalse(composite.getEnabled());
 	}
 
+	public void testAddScrollListener() {
+		Scrollable textWidget = new Composite(WorkbenchUtil.getShell(), SWT.V_SCROLL);
+
+		assertNotNull(textWidget.getVerticalBar());
+		assertEquals(0, textWidget.getListeners(SWT.MouseVerticalWheel).length);
+
+		EditorUtil.addScrollListener(textWidget);
+		assertEquals(1, textWidget.getListeners(SWT.MouseVerticalWheel).length);
+
+		// test when there is no vertical bar
+		textWidget = new Composite(WorkbenchUtil.getShell(), SWT.NONE);
+		assertNull(textWidget.getVerticalBar());
+
+		assertEquals(0, textWidget.getListeners(SWT.MouseVerticalWheel).length);
+
+		EditorUtil.addScrollListener(textWidget);
+		assertEquals(1, textWidget.getListeners(SWT.MouseVerticalWheel).length);
+	}
+
 }
diff --git a/org.eclipse.mylyn.tasks.ui/src/org/eclipse/mylyn/internal/tasks/ui/editors/EditorUtil.java b/org.eclipse.mylyn.tasks.ui/src/org/eclipse/mylyn/internal/tasks/ui/editors/EditorUtil.java
index 958668dd5..da0a22f6d 100644
--- a/org.eclipse.mylyn.tasks.ui/src/org/eclipse/mylyn/internal/tasks/ui/editors/EditorUtil.java
+++ b/org.eclipse.mylyn.tasks.ui/src/org/eclipse/mylyn/internal/tasks/ui/editors/EditorUtil.java
@@ -546,28 +546,26 @@ public class EditorUtil {
 	}
 
 	public static void addScrollListener(final Scrollable textWidget) {
-		if (textWidget.getVerticalBar() != null) {
-			textWidget.addMouseWheelListener(new MouseWheelListener() {
-				public void mouseScrolled(MouseEvent event) {
-					ScrolledComposite form = FormUtil.getScrolledComposite(textWidget);
-					if (form != null) {
-						ScrollBar verticalBar = textWidget.getVerticalBar();
-						if (event.count < 0) {
-							// scroll form down
-							if (verticalBar == null
-									|| verticalBar.getSelection() + verticalBar.getThumb() == verticalBar.getMaximum()) {
-								EditorUtil.scroll(form, 0, form.getVerticalBar().getIncrement());
-							}
-						} else {
-							// scroll form up
-							if (verticalBar == null || verticalBar.getSelection() == verticalBar.getMinimum()) {
-								EditorUtil.scroll(form, 0, -form.getVerticalBar().getIncrement());
-							}
+		textWidget.addMouseWheelListener(new MouseWheelListener() {
+			public void mouseScrolled(MouseEvent event) {
+				ScrolledComposite form = FormUtil.getScrolledComposite(textWidget);
+				if (form != null) {
+					ScrollBar verticalBar = textWidget.getVerticalBar();
+					if (event.count < 0) {
+						// scroll form down
+						if (verticalBar == null
+								|| verticalBar.getSelection() + verticalBar.getThumb() == verticalBar.getMaximum()) {
+							EditorUtil.scroll(form, 0, form.getVerticalBar().getIncrement());
+						}
+					} else {
+						// scroll form up
+						if (verticalBar == null || verticalBar.getSelection() == verticalBar.getMinimum()) {
+							EditorUtil.scroll(form, 0, -form.getVerticalBar().getIncrement());
 						}
 					}
 				}
-			});
-		}
+			}
+		});
 	}
 
 	public static void addScrollListener(final CCombo combo) {