Renderer lưới tạo ra một phần tử HTML cho các thành phần UIPanel. Bảng điều khiển làm cho con của nó để nó có thể quản lý bố trí bằng cách vẽ các thành phần bên trong các hàng và các tế bào của bảng. Đây là đoạn mã cho việc mở cửa của thẻ panelGrid từ để tham khảo nhanh chóng. | 268 Chapter 7 The listener can also be registered programmatically by calling addAc-tionListener on the target ActionSource . FacesContext context UIViewRoot view ActionSource button ActionSource saveButton if component null new UserActionListener . We could then access the UserActions bean in the session whenever we wanted to display the tracked actions . FacesContext context ValueBinding binding userActions UserActions actions UserActions context User Actions actions . The resulting log entries would look something like the following . Mon Mar 22 00 06 09 EST 2004 command Save page component invoiceForm saveButton Mon Mar 22 00 06 10 EST 2004 command Confirm page component invoiceForm confirmButton Mon Mar 22 00 06 17 EST 2004 command Save page component invoiceForm saveButton Mon Mar 22 00 06 20 EST 2004 command Confirm page component invoiceForm confirmButton Implementing a ValueChangeListener Method Although ValueChageListeners are primarily intended to be used in implementing custom components also true of ActionListeners though perhaps to a lesser extent they can also be used directly either as methods on a backing bean or in the form of classes that implement the ValueChange Listener interface. Let s look at a concrete example of where it might make sense to use a ValueChangeListener method adding support for an undo button on the Modify Invoice page from Listing . Navigation Actions and Listeners 269 First we will need to implement an undo manager. Here s a very simple one package import import import import public class UndoManager implements Serializable private class .
