Added Transaction for executeWithRedrawDisabled

After Review by @HeikoKlare in eclipse-platform#1072, this method
allows for other methods to perform costly operations on
an undrawn tree without manually dis- and re-enabling the tree.

bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java

@@ -800,16 +800,15 @@ public void collapseAll() {
 	 */
 	public void collapseToLevel(Object elementOrTreePath, int level) {
 		Assert.isNotNull(elementOrTreePath);
-		Control control = getControl();
-		try {
-			control.setRedraw(false);
-			Widget w = internalGetWidgetToSelect(elementOrTreePath);
-			if (w != null) {
-				internalCollapseToLevel(w, level);
+		executeWithRedrawDisabled(new Runnable() {
+			@Override
+			public void run() {
+				Widget w = internalGetWidgetToSelect(elementOrTreePath);
+				if (w != null) {
+					internalCollapseToLevel(w, level);
+				}
 			}
-		} finally {
-			control.setRedraw(true);
-		}
+		});
 	}
 
 	/**
@@ -1169,20 +1168,15 @@ public void expandToLevel(Object elementOrTreePath, int level) {
 	public void expandToLevel(Object elementOrTreePath, int level, boolean disableRedraw) {
 		if (checkBusy())
 			return;
-		Control control = getControl();
-		try {
-			if (disableRedraw) {
-				control.setRedraw(false);
-			}
-			Widget w = internalExpand(elementOrTreePath, true);
-			if (w != null) {
-				internalExpandToLevel(w, level);
-			}
-		} finally {
-			if (disableRedraw) {
-				control.setRedraw(true);
+		executeWithRedrawDisabled(new Runnable() {
+			@Override
+			public void run() {
+				Widget w = internalExpand(elementOrTreePath, true);
+				if (w != null) {
+					internalExpandToLevel(w, level);
+				}
 			}
-		}
+		}, disableRedraw);
 	}
 
 	/**
@@ -1643,15 +1637,15 @@ public void treeCollapsed(TreeEvent event) {
 	@Override
 	protected void inputChanged(Object input, Object oldInput) {
 		preservingSelection(() -> {
-			Control tree = getControl();
-			tree.setRedraw(false);
-			try {
-				removeAll(tree);
-				tree.setData(getRoot());
-				internalInitializeTree(tree);
-			} finally {
-				tree.setRedraw(true);
-			}
+			executeWithRedrawDisabled(new Runnable() {
+				@Override
+				public void run() {
+					Control tree = getControl();
+					removeAll(tree);
+					tree.setData(getRoot());
+					internalInitializeTree(tree);
+				}
+			});
 		});
 	}
 
@@ -2336,12 +2330,13 @@ private boolean isExpandable(Item item, TreePath parentPath, Object element) {
 
 	@Override
 	protected void labelProviderChanged() {
-		// we have to walk the (visible) tree and update every item
-		Control tree = getControl();
-		tree.setRedraw(false);
-		// don't pick up structure changes, but do force label updates
-		internalRefresh(tree, getRoot(), false, true);
-		tree.setRedraw(true);
+		executeWithRedrawDisabled(new Runnable() {
+			@Override
+			public void run() {
+				Control tree = getControl();
+				internalRefresh(tree, getRoot(), false, true);
+			}
+		});
 	}
 
 	/**
@@ -3517,7 +3512,7 @@ public boolean contains(Object parent, Object element) {
 	}
 
 	/**
-	 * Returns wether the given Widget is a single child. Used as functional
+	 * Returns whether the given Widget is a single child. Used as functional
 	 * Parameter to {@link #internalConditionalExpandToLevel(Widget, int, Function)}
 	 * while expanding paths of single children
 	 * {@link #setAutoExpandOnSingleChildLevel(int)}
@@ -3530,4 +3525,38 @@ private boolean doesWidgetHaveExactlyOneChild(Widget w) {
 		return getChildren(w).length == 1;
 	}
 
+	/**
+	 * Transactionally perform an action on the TreeViewer without redrawing
+	 * regularly. Disables redraw, executes toExecute and enables redraw again.
+	 *
+	 * @param toExecute the transaction to execute on the TreeViewer while it is not
+	 *                  reDrawing
+	 *
+	 */
+	private void executeWithRedrawDisabled(Runnable toExecute) {
+		executeWithRedrawDisabled(toExecute, true);
+	}
+
+	/**
+	 * Transactionally perform an action on the TreeViewer without redrawing
+	 * regularly. Disables redraw, executes toExecute and enables redraw again.
+	 *
+	 * @param toExecute the transaction to execute on the TreeViewer while it is not
+	 *                  reDrawing
+	 *
+	 */
+	private void executeWithRedrawDisabled(Runnable toExecute, boolean shouldDisableRedraw) {
+		Control control = getControl();
+		try {
+			if (shouldDisableRedraw) {
+				control.setRedraw(false);
+			}
+			toExecute.run();
+		} finally {
+			if (shouldDisableRedraw) {
+				control.setRedraw(true);
+			}
+		}
+	}
+
 }