Vaadin Web应用开发教程(20):UI组件-MenuBar组件

MenuBar 用来创建下拉菜单，类似桌面应用的菜单显示。
使用MenuBar首先创建MenuBar的实例：

[java] 
// Create a menu bar  
final MenuBar menubar = new MenuBar(); 
main.addComponent(menubar); 

// Create a menu bar
final MenuBar menubar = new MenuBar();
main.addComponent(menubar);
然后通过addItem 为最上一级菜单添加菜单项，addItem 参数为String，一个图标资源，一个Command 对象(用户点击菜单项后所执行命令）。 icon 和command 可以为空。
Command对象为实现了MenuBar.Command 接口的对象，如：

[java] 
// A feedback component  
final Label selection = new Label("-"); 
main.addComponent(selection); 
 
// Define a common menu command for all the menu items.  
MenuBar.Command mycommand = new MenuBar.Command() { 
    public void menuSelected(MenuItem selectedItem) { 
        selection.setValue("Ordered a " + 
                           selectedItem.getText() + 
                           " from menu."); 
    }   
}; 

// A feedback component
final Label selection = new Label("-");
main.addComponent(selection);

// Define a common menu command for all the menu items.
MenuBar.Command mycommand = new MenuBar.Command() {
    public void menuSelected(MenuItem selectedItem) {
        selection.setValue("Ordered a " +
                           selectedItem.getText() +
                           " from menu.");
    } 
};

 addItem() 方法返回一个MenuBar.MenuItem 对象，利用这个返回值，你可以参加子菜单。MenuItem 也有同样的addItem 方法。

[java] 
// Put some items in the menu hierarchically  
MenuBar.MenuItem beverages = 
    menubar.addItem("Beverages", null, null); 
MenuBar.MenuItem hot_beverages = 
    beverages.addItem("Hot", null, null); 
hot_beverages.addItem("Tea", null, mycommand); 
hot_beverages.addItem("Coffee", null, mycommand); 
MenuBar.MenuItem cold_beverages = 
    beverages.addItem("Cold", null, null); 
cold_beverages.addItem("Milk", null, mycommand); 
 
// Another top-level item  
MenuBar.MenuItem snacks = 
    menubar.addItem("Snacks", null, null); 
snacks.addItem("Weisswurst", null, mycommand); 
snacks.addItem("Salami", null, mycommand); 
 
// Yet another top-level item  
MenuBar.MenuItem services = 
    menubar.addItem("Services", null, null); 
services.addItem("Car Service", null, mycommand); 

// Put some items in the menu hierarchically
MenuBar.MenuItem beverages =
    menubar.addItem("Beverages", null, null);
MenuBar.MenuItem hot_beverages =
    beverages.addItem("Hot", null, null);
hot_beverages.addItem("Tea", null, mycommand);
hot_beverages.addItem("Coffee", null, mycommand);
MenuBar.MenuItem cold_beverages =
    beverages.addItem("Cold", null, null);
cold_beverages.addItem("Milk", null, mycommand);

// Another top-level item
MenuBar.MenuItem snacks =
    menubar.addItem("Snacks", null, null);
snacks.addItem("Weisswurst", null, mycommand);
snacks.addItem("Salami", null, mycommand);

// Yet another top-level item
MenuBar.MenuItem services =
    menubar.addItem("Services", null, null);
services.addItem("Car Service", null, mycommand);

显示结果如下：

补充：Web开发 , 其他 ,

上一个：Vaadin Web应用开发教程(21):UI组件-Embedded组件
下一个：html各种表格