Description Albert 2011-01-24 06:15:13 EST

I want to set correct DND.FEEDBACK_INSERT_BEFORE and DND.FEEDBACK_INSERT_AFTER when dragging TableItems inside dragOver method. Although feedback indicator appears, this can result in wrong indication where item will be dropped; expected drop position is different from the actual position after drop.

Please, consider this DND example: http://www.java2s.com/Code/Java/SWT-JFace-Eclipse/SWTDNDDrag andDropcomprehensiveExample.htm

Run the example and check the following options:

Inside the left-hand pane:

- select "Table" from the Combo,
- check Drag Source check box,
- check DND.DROP_MOVE,
- check the Text Transfer check box

Inside the right-hand pane:

- select "Table" from the Combo,
- check Drag Target check box,
- check the Text Transfer check box,
- check DND.DROP_MOVE,
- check DND.FEEDBACK_INSERT_BEFORE,
- check DND.FEEDBACK_INSERT_AFTER

Now if you drag a TableItem from the left-hand Table UP the destination table so that mouse pointer is at highest possible position before insertion line jumps one item higher (not so simple to achieve, since we have to move mouse pixel by pixel up the destination Table), insertion line indicates that this item will be dropped AFTER the item. But once we release the mouse button, and drop takes place, item is unexpectedly dropped BEFORE the item.

This happens only on Mac, while it works perfectly on Windows (haven't tried with GTK yet though).

The other issue (I think it's related to this one, so I'm not opening another bug) is the following:

inside the dragOver method, where I want to set correct feedback (insertion line) depending on mouse pointer location inside the TableItem, this results in chaotic jumping of insertion line. This is a bit hard to describe, but the point is that this straight forward piece of code that I can use without problems when dragging over TreeItems fails on Mac. Code for determining event location that I use:

TableItem item = (TableItem) event.item;
Point point = item.getParent().getDisplay().map(null, item.getParent(), event.x, event.y);
Rectangle bounds = item.getBounds();
        
if (point.y < bounds.y + bounds.height / 2)
{
    // Event location in the upper half of TableItem
    event.feedback |= DND.FEEDBACK_INSERT_BEFORE;
}        
else if (point.y >= bounds.y + bounds.height / 2)
{
    // Event location in the lower half of TableItem
    event.feedback |= DND.FEEDBACK_INSERT_AFTER;
}

Again, this code works perfectly on Windows with Tree and also with Table. It won't work with Table on Mac.

Here is a complete runnable snippet that demonstrates insertion line jumping inside dragOver method on Mac. Methods dragEnter and drop are not implemented:

import org.eclipse.swt.SWT;
import org.eclipse.swt.dnd.DND;
import org.eclipse.swt.dnd.DragSource;
import org.eclipse.swt.dnd.DragSourceAdapter;
import org.eclipse.swt.dnd.DragSourceEvent;
import org.eclipse.swt.dnd.DropTarget;
import org.eclipse.swt.dnd.DropTargetAdapter;
import org.eclipse.swt.dnd.DropTargetEvent;
import org.eclipse.swt.dnd.TextTransfer;
import org.eclipse.swt.dnd.Transfer;
import org.eclipse.swt.graphics.Point;
import org.eclipse.swt.graphics.Rectangle;
import org.eclipse.swt.layout.GridData;
import org.eclipse.swt.layout.GridLayout;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;
import org.eclipse.swt.widgets.Table;
import org.eclipse.swt.widgets.TableItem;

public class DragOverTable
{   
    private final static int UPPER_HALF = 1;        
    private final static int LOWER_HALF = -1;
    
    private static Table table;    
    
    public static void main (String [] args)
    {
        Display display = new Display();
        
        Shell shell = new Shell(display);
        shell.setLayout(new GridLayout());
        table = new Table(shell, SWT.MULTI | SWT.BORDER | SWT.FULL_SELECTION);
        GridData data = new GridData(SWT.FILL, SWT.FILL, true, true);
        data.heightHint = 200;
        data.widthHint = 200;
        table.setLayoutData(data);
        table.setLinesVisible(true);
        table.setHeaderVisible(true);
            
        int count = 40;
        for (int i = 0; i < count; i++)
        {
            TableItem item = new TableItem(table, SWT.NONE);
            item.setText("TableItem " + i);
        }
        
        // Drag and drop
        Transfer[] types = new Transfer[] {TextTransfer.getInstance()};
        
        // Define drag source
        DragSource source = new DragSource(table, DND.DROP_MOVE);
        source.setTransfer(types);
        
        source.addDragListener(new DragSourceAdapter()
        {
            public void dragSetData(DragSourceEvent event)
            {
                // Set some dummy data to prevent crash due to a
                // "Data does not have correct format for type" exception
                // when releasing mouse button
                event.data = " ";
            }
        });

        // Define the drop target
        DropTarget target = new DropTarget(table, DND.DROP_MOVE | DND.DROP_DEFAULT);
        target.setTransfer(types);
        target.addDropListener(new DropTargetAdapter()
        {
            public void dragEnter(DropTargetEvent event)
            {
                // Not implemented
            }

            public void dragOver(DropTargetEvent event)
            {   
                if (event.item == null)
                {   
                    event.feedback = DND.DROP_NONE;
                    return;
                }
                
                event.feedback = DND.FEEDBACK_SCROLL;
                
                // Set correct insertion line depending on the pointer position
                // inside a table item
                switch (eventLocation(event))
                {   
                    case UPPER_HALF:                       
                        event.feedback |= DND.FEEDBACK_INSERT_BEFORE;                        
                        break;                 
                    case LOWER_HALF:                       
                        event.feedback |= DND.FEEDBACK_INSERT_AFTER;                        
                        break;
                    default:
                        break;
                }
            }                
            
            public void drop(DropTargetEvent event)
            {
                // Not implemented
            }
        });
        
        shell.pack ();
        shell.open ();
        
        while (!shell.isDisposed ())
        {
            if (!display.readAndDispatch())
            {
                display.sleep();
            }   
        }
        display.dispose ();
    }
    
    private static int eventLocation(DropTargetEvent event)
    {
        TableItem item = (TableItem) event.item;
        Point point = item.getParent().getDisplay().map(null, item.getParent(), event.x, event.y);
        Rectangle bounds = item.getBounds();
        
        if (point.y < bounds.y + bounds.height / 2)
        {
            // Pointer is in the upper half of TableItem
            return UPPER_HALF;
        }        
        else if (point.y >= bounds.y + bounds.height / 2)
        {
            // Pointer is in the lower half of TableItem
            return LOWER_HALF;
        }
        else
        {
            return 0;
        }
}

Is this a bug? I can't see a programming mistake here, am I overlooking something?