[news.eclipse.platform.swt] Re: Mouse scroll leads to different event ra

[wangwcdl@xxxxxxxxxx (Wang Wei)]

I've written a snippet to demonstrate the platform difference existing on 
the two platforms. I've created a canvas on a shell and added selection 
listener to the canvas' vertical scrollbar. On MAC platform, selection 
event's detail is SWT.PAGE_UP or SWT.PAGE_DOWN when scrolling the mouse 
while on windows platform, selection event's detail is SWT.ARROW_UP or 
SWT.ARROW_DOWN.

In our custom table control, we draw the content on a canvas and add a 
selection listener to table's vertical scrollbar. As SWT.PAGE_DOWN is sent 
to this listener when mouse scrolls on MAC platform, table's content 
scrolls to another page. This behaviour is not what the user wants. 
Although we could capture SWT.MOUSE_WHEEL event, I don't know how to 
establish the relationship between mouse wheel event and scrollbar's 
selection events. 

As a matter of fact, I think this is a bug of SWT on MAC platform. When 
mouse wheel is moved, I think it's not quite reasonable to send 
SWT.PAGE_UP/SWT.PAGE_DOWN events.

The following is the snippet I've written. 

package snippets;

import org.eclipse.swt.SWT;
import org.eclipse.swt.events.SelectionEvent;
import org.eclipse.swt.events.SelectionListener;
import org.eclipse.swt.widgets.Canvas;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;

public class ScrollBarTest {

public static void main (String [] args) {
	Display display = new Display ();
	Shell shell = new Shell (display);
	
	final Canvas canvas = new Canvas(shell, SWT.BORDER | SWT.V_SCROLL);
	canvas.setBackground(display.getSystemColor(SWT.COLOR_BLUE));
	canvas.setSize(280, 700);
	
	if(canvas.getVerticalBar() != null) {
		canvas.getVerticalBar().addSelectionListener(new SelectionListener(){
			
			public void widgetDefaultSelected(SelectionEvent e) {
			}
			
			public void widgetSelected(SelectionEvent e) {
				switch(e.detail) {
				case SWT.PAGE_DOWN:
					System.out.println("Selection event detail is page down. ");
					break;
				case SWT.PAGE_UP:
					System.out.println("Selection event detail is page up. ");
					break;
				case SWT.ARROW_DOWN:
					System.out.println("Selection event detail is arrow down. ");
					break;
				case SWT.ARROW_UP:
					System.out.println("Selection event detail is arrow up. ");
					break;
				};
				 
			}});
	}

	shell.setSize(300, 200);
	shell.open ();
	while (!shell.isDisposed ()) {
		if (!display.readAndDispatch ()) display.sleep ();
	}
	display.dispose ();
}
}