Bug 189847 [DND] Combo/Text on Linux does not fire Drop event.
examples/org.eclipse.swt.examples/src/org/eclipse/swt/examples/dnd/DNDExample.java
for (int i = 0; i < dragTypes.length; i++) {
				if (dragTypes[i] instanceof TextTransfer && dragDataText == null) {
					event.doit = false;
				}
				if (dragTypes[i] instanceof RTFTransfer && dragDataRTF == null) {
					event.doit = false;
				}
				if (dragTypes[i] instanceof HTMLTransfer && dragDataHTML == null) {
					event.doit = false;
				}
				if (dragTypes[i] instanceof FileTransfer && (dragDataFiles == null || dragDataFiles.length == 0)) {
					event.doit = false;
				}
			}
		}
	});
}
private void createDragTypes(Composite parent) {
	parent.setLayout(new GridLayout());
	Button textButton = new Button(parent, SWT.CHECK);
	textButton.setText("Text Transfer");
	textButton.addSelectionListener(new SelectionAdapter() {
		public void widgetSelected(SelectionEvent e) {
			Button b = (Button)e.widget;
			if (b.getSelection()) {
				addDragTransfer(TextTransfer.getInstance());			
			} else {
				removeDragTransfer(TextTransfer.getInstance());
			}
		}