Vaadin Web应用开发课程(19):UI组件-Tree 组件

Tree 组件可以用来显示具有层次关系的数据源，比如文件系统。Tree组件的一个典型应用是作为菜单显示。

final Object[][] planets = new Object[][]{
        new Object[]{"Mercury"},
        new Object[]{"Venus"},
        new Object[]{"Earth", "The Moon"},
        new Object[]{"Mars", "Phobos", "Deimos"},
        new Object[]{"Jupiter", "Io", "Europa", "Ganymedes",
                                "Callisto"},
        new Object[]{"Saturn",  "Titan", "Tethys", "Dione",
                                "Rhea", "Iapetus"},
        new Object[]{"Uranus",  "Miranda", "Ariel", "Umbriel",
                                "Titania", "Oberon"},
        new Object[]{"Neptune", "Triton", "Proteus", "Nereid",
                                "Larissa"}};

Tree tree = new Tree("The Planets and Major Moons");

// Add planets as root items in the tree.
for (int i=0; i    String planet = (String) (planets[i][0]);
    tree.addItem(planet);

    if (planets[i].length == 1) {
        // The planet has no moons so make it a leaf.
        tree.setChildrenAllowed(planet, false);
    } else {
        // Add children (moons) under the planets.
        for (int j=1; j            String moon = (String) planets[i][j];

            // Add the item as a regular item.
            tree.addItem(moon);

            // Set it to be a child.
            tree.setParent(moon, planet);

            // Make the moons look like leaves.
            tree.setChildrenAllowed(moon, false);
        }

        // Expand the subtree.
        tree.expandItemsRecursively(planet);
    }
}

main.addComponent(tree);

当然你可以选择合适的Menu风格使得Tree看起来更像菜单，比如：

注：到这里你可能注意到到目前为止在介绍UI组件时文章都避免涉及CSS，Theme应用，这是为的使Vaadin应用开发更像开发桌面应用，后面会集中介绍主题的使用，对于一般应用你可以使用缺省主题。

同Field组件一样，你可以使用getValue,setValue 设置或取得Tree组件当前选中的Item项。Tree组件对应的Container类型为HierarchicalContainer.