1 files changed, 1 insertions, 0 deletions

diff --git a/examples/org.eclipse.swt.examples/src/org/eclipse/swt/examples/fileviewer/TreeScrollDropListener.java b/examples/org.eclipse.swt.examples/src/org/eclipse/swt/examples/fileviewer/TreeScrollDropListener.java
new file mode 100755
index 0000000000..5c7c8d8ad7
--- /dev/null
+++ b/examples/org.eclipse.swt.examples/src/org/eclipse/swt/examples/fileviewer/TreeScrollDropListener.java
@@ -0,0 +1 @@
+package org.eclipse.swt.examples.fileviewer;

/*
 * (c) Copyright IBM Corp. 2000, 2001.
 * All Rights Reserved
 */

import org.eclipse.swt.dnd.*;
import org.eclipse.swt.graphics.*;
import org.eclipse.swt.widgets.*;

/**
 * TreeScrollDropListener provides automatic scrolling for Trees during drag and drop
 * operations.
 * <p>
 * If the pointer drags over an item in the Tree near its upper or
 * lower edges, the Tree will scroll so as to make previous or successive items visible
 * onscreen.  This behaviour is consistent with that of popular GUI systems.
 * </p><p>
 * To use it send addDropListener(new TreeScrollDropListener(tree)) to the DropTarget
 * object attached to the Tree.
 * </p>
 */
public class TreeScrollDropListener extends DropTargetAdapter {
	private Tree tree;
	
	/**
	 * Constructs a Tree scrolling Drop Listener
	 * 
	 * @param tree the Tree that the DropTarget is attached to
	 */
	public TreeScrollDropListener(final Tree tree) {
		this.tree = tree;
	}

	/**
	 * Handles dragOver events.
	 * This is an implementation detail.
	 */
	public void dragOver(DropTargetEvent event) {
		Point point = tree.toControl(new Point(event.x, event.y));

		// Get the item directly under the point
		TreeItem item = tree.getItem(point);
		if (item == null) return;


		// Determine scroll direction according to whether we're nearer the top, middle, or bottom
		Rectangle clientArea = tree.getClientArea();
		int scrollRegionSize = Math.min(clientArea.height / 3, 24); // cut region into 3 parts
		if (scrollRegionSize < 8) return; // don't scroll if the control is too small to make sense
		
		TreeItem showItem = item;
		for(;;) {
			if (point.y < clientArea.y + scrollRegionSize) {
				// in upper region
				showItem = getPreviousVisibleItem(tree, showItem);
			} else if (point.y > clientArea.height + clientArea.y - scrollRegionSize) {
				// in lower region
				showItem = getNextVisibleItem(tree, showItem, false);
			} else {
				// in middle region
				break;
			}
			
			// Show the item (causes a scroll if it is outside of the visible region)
			if (showItem == null) break;		
			tree.showItem(showItem);
			
			// Test that we actually scrolled, if we didn't try again with the next item
			if (item != tree.getItem(point)) break;
		}
	}

	/**
	 * Given a TreeItem, locates the previous (above the specified item) visible TreeItem in a tree.
	 * <p>
	 * Note that the item may not be actually rendered onscreen though it would be
	 * visible were the control scrolled appropriately.
	 * </p>
	 * 
	 * @param tree the Tree containing the items
	 * @param item the TreeItem whose previous visible neighbour is to be found
	 * @return the previous visible item, or null if none.
	 */
	private TreeItem getPreviousVisibleItem(Tree tree, TreeItem item) {
		TreeItem parent = item.getParentItem();
		TreeItem[] items = (parent != null) ? parent.getItems() : tree.getItems();
		if (items != null) {
			for (int i = items.length - 1; i > 0; --i) {
				if (items[i] == item) return getLastVisibleChild(items[i - 1]);
			}
		}
		return parent;
	}


	/**
	 * Given a TreeItem, locates the following (below the specified item) visible TreeItem in a tree.
	 * <p>
	 * Note that the item may not be actually rendered onscreen though it would be
	 * visible were the control scrolled appropriately.
	 * </p>
	 * 
	 * @param tree the Tree containing the items
	 * @param item the TreeItem whose next visible neighbour is to be found
	 * @return the next visible item, or null if none.
	 */
	private TreeItem getNextVisibleItem(Tree tree, TreeItem item, boolean ignoreChildren) {
		TreeItem parent = item.getParentItem();
		TreeItem[] items = (parent != null) ? parent.getItems() : tree.getItems();
		if (items != null) {
			for (int i = 0; i < items.length; ++i) {
				if (items[i] == item) {
					if (! ignoreChildren && items[i].getExpanded()) {
						items = items[i].getItems();
						if (items != null && items.length > 0) return items[0];
					}
					if (i + 1 < items.length) return items[i + 1];
					break;
				}
			}
			if (parent != null) return getNextVisibleItem(tree, parent, true);
		}
		return null;
	}

	/**
	 * Given a TreeItem, locates its last (lowest) visible item
	 * <p>
	 * Note that the item may not be actually rendered onscreen though it would be
	 * visible were the control scrolled appropriately.
	 * </p>
	 * 
	 * @param item the TreeItem whose last visible child is to be found
	 * @return the last visible child, or <code>item</code> if no visible children.
	 */
	private TreeItem getLastVisibleChild(TreeItem item) {
		if (! item.getExpanded()) return item;
		
		TreeItem[] items = item.getItems();
		if (items == null || items.length == 0) return item;
		return getLastVisibleChild(items[items.length - 1]);
	}
}
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