Use exportField.setHoverCustomizer()
to show a customized prompt message.
Try this one
ListGrid grid = new ListGrid();
grid.setCanHover(true);
grid.setShowHover(true);
...
exportField.setHoverCustomizer(new HoverCustomizer() {
@Override
public String hoverHTML(Object value, ListGridRecord record, int rowNum, int colNum) {
// you can customize the prompt and can get the values from current record also
return "a tooltip message";
}
});