[news.eclipse.platform.swt] Re: SWT stops processing events when draggin

[maxx <ainews@xxxxxxxx>]

... here is the missing snippet:

maxx schrieb:
> Hy there,
>
> when a drag-operation starts, it seems that SWT stops processing events 
> until either the mouse is moved or the button is released.
>
> To reproduce the behavior, start the test given below and position your 
> mouse-pointer above a tree-item. As soon as you push down the left 
> mouse-button the counter will stop ...
>
> Is this expected behavior ?
>
> I work on an application which shows quite a lot of real-time updated 
> information. As soon as the mouse-button is pressed on any of the 
> drag-drop enabled components *everything* in the GUI freezes, and SWT 
> pollutes its async-queue with a ton of events. These events will then be 
> "post" processed, ie. they get processed as soon as the mouse 
> moves/releases.
>
> Thanks in advance
> maxx

import org.eclipse.swt.SWT;
import org.eclipse.swt.events.DisposeListener;
import org.eclipse.swt.events.DisposeEvent;
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.layout.FillLayout;
import org.eclipse.swt.widgets.Button;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;
import org.eclipse.swt.widgets.Tree;
import org.eclipse.swt.widgets.TreeItem;

public class DragNUpdateTest
{

    static Button button;
    static boolean running = false;


    public static void main(String[] args)
    {
        Shell shell = new Shell();
        shell.setLayout(new FillLayout());
        shell.addDisposeListener(new DisposeListener()
        {
            public void widgetDisposed(DisposeEvent event)
            {
                running = false;
            }
        });

        // Create the tree and some tree items
        final Tree tree = new Tree(shell, SWT.NONE);
        TreeItem item1 = new TreeItem(tree, SWT.NONE);
        item1.setText("Item 1");
        TreeItem item2 = new TreeItem(tree, SWT.NONE);
        item2.setText("Item 2");
        TreeItem item3 = new TreeItem(tree, SWT.NONE);
        item3.setText("Item 3");
        TreeItem item4 = new TreeItem(tree, SWT.NONE);
        item4.setText("Item 4");

        // Create the drag source on the tree
        DragSource ds = new DragSource(tree, DND.DROP_MOVE);
        ds.setTransfer(new Transfer[]{TextTransfer.getInstance()});
        ds.addDragListener(new DragSourceAdapter()
        {
            public void dragSetData(DragSourceEvent event)
            {
                // Set the data to be the first selected item's text
                event.data = tree.getSelection()[0].getText();
            }
        });

        // Create the button
        button = new Button(shell, SWT.FLAT);
        button.setText("Button");
        button.setAlignment(SWT.CENTER);
        button.setData(0);

        // Create the drop target on the button
        DropTarget dt = new DropTarget(button, DND.DROP_MOVE);
        dt.setTransfer(new Transfer[]{TextTransfer.getInstance()});
        dt.addDropListener(new DropTargetAdapter()
        {
            public void drop(DropTargetEvent event)
            {
                // Set the buttons text to be the text being dropped
                button.setText((String) event.data);
            }
        });

        shell.pack();
        shell.open();

        startUpdater();

        Display display = Display.getDefault();
        while (!shell.isDisposed())
            if (!display.readAndDispatch())
                display.sleep();
        display.dispose();
    }

    private static void startUpdater()
    {
        Thread updateThread = new Thread(new Runnable()
        {
            public void run()
            {
                while (running)
                {
                    Display.getDefault().asyncExec(new Runnable()
                    {
                        public void run()
                        {
                            if (!running)
                                return;
                            int val = (Integer) button.getData() + 1;
                            button.setData(val);
                            button.setText(String.valueOf(val));
                        }
                    });

                    try
                    {
                        Thread.sleep(200);
                    }
                    catch (InterruptedException e)
                    {
                    }
                }
            }
        });

        running = true;
        updateThread.start();
    }


}