5.13. Selecting Items
Vaadin gives many alternatives for selecting one or more items from a list, using drop-down and regular lists, radio button and check box groups, tables, trees, and so on.
The core library includes the following selection components, all based on the AbstractSelect class:
Select- In single selection mode, a drop-down list with a text input area, which the user can use to filter the displayed items. In multiselect mode, a list box equivalent to
ListSelect. ComboBox- A drop-down list for single selection. Otherwise as
Select, but the user can also enter new items. The component also provides an input prompt. ListSelect- A vertical list box for selecting items in either single or multiple selection mode.
NativeSelect- Provides selection using the native selection component of the browser, typically a drop-down list for single selection and a multi-line list in multiselect mode. This uses the
<select>element in HTML. OptionGroup- Shows the items as a vertically arranged group of radio buttons in the single selection mode and of check boxes in multiple selection mode.
TwinColSelect- Shows two list boxes side by side where the user can select items from a list of available items and move them to a list of selected items using control buttons.
In addition, the Tree and Table components allow special forms of selection. They also inherit the AbstractSelect.
The selection components are strongly coupled with the Vaadin Data Model. The selectable items in all selection components are objects that implement the Item interface and are contained in a Container. The current selection is bound to the Property interface.
Even though the data model is used, the selection components allow simple use in the most common cases. Each selection component is bound to a default container type, which supports management of items without need to implement a container.
See Chapitre 9, Liaison des Composants avec les Données for a detailed description of the data model, its interfaces, and built-in implementations.
New items are added with the addItem() method defined in the Container interface.
// Create a selection component
Select select = new Select ("Select something here");
// Add some items and give each an item ID
select.addItem("Mercury");
select.addItem("Venus");
select.addItem("Earth");
The addItem() method creates an empty Item, which is identified by its item identifier (IID) object, given as the parameter. This item ID is by default used also as the caption of the item, as explained in the next section. The identifier is typically a String. The item is of a type specific to the container and has itself little relevance for most selection components, as the properties of an item may not be used in any way (except in Table), only the item ID.
The item identifier can be of any object type. We could as well have given integers for the item identifiers and set the captions explicitly with setItemCaption(). You could also add an item with the parameterless addItem(), which returns an automatically generated item ID.
// Create a selection component
Select select = new Select("My Select");
// Add an item with a generated ID
Object itemId = select.addItem();
select.setItemCaption(itemId, "The Sun");
// Select the item
select.setValue(itemId);
Some container types may support passing the actual data object to the add method. For example, you can add items to a BeanItemContainer with addBean(). Such implementations can use a separate item ID object, or the data object itself as the item ID, as is done in addBean(). In the latter case you can not depend on the default way of acquiring the item caption; see the description of the different caption modes later.
The following section describes the different options for determining the item captions.
The displayed captions of items in a selection component can be set explicitly with setItemCaption() or determined from the item IDs or item properties. This behaviour is defined with the caption mode, which you can set with setItemCaptionMode(). The default mode is ITEM_CAPTION_MODE_EXPLICIT_DEFAULTS_ID, which uses the item identifiers for the captions, unless given explicitly.
In addition to a caption, an item can have an icon. The icon is set with setItemIcon().
Caption Modes for Selection Components
ITEM_CAPTION_MODE_EXPLICIT_DEFAULTS_ID-
This is the default caption mode and its flexibility allows using it in most cases. By default, the item identifier will be used as the caption. The identifier object does not necessarily have to be a string; the caption is retrieved with
toString()method. If the caption is specified explicitly withsetItemCaption(), it overrides the item identifier.Select select = new Select("Moons of Mars"); // Use the item ID also as the caption of this item select.addItem(new Integer(1)); // Set item caption for this item explicitly select.addItem(2); // same as "new Integer(2)" select.setItemCaption(2, "Deimos"); ITEM_CAPTION_MODE_EXPLICIT-
Captions must be explicitly specified with
setItemCaption(). If they are not, the caption will be empty. Such items with empty captions will nevertheless be displayed in theSelectcomponent as empty items. If they have an icon, they will be visible. ITEM_CAPTION_MODE_ICON_ONLY-
Only icons are shown, captions are hidden.
ITEM_CAPTION_MODE_ID-
String representation of the item identifier object is used as caption. This is useful when the identifier is a string, and also when the identifier is an complex object that has a string representation. For example:
Select select = new Select("Inner Planets"); select.setItemCaptionMode(Select.ITEM_CAPTION_MODE_ID); // A class that implements toString() class PlanetId extends Object implements Serializable { String planetName; PlanetId (String name) { planetName = name; } public String toString () { return "The Planet " + planetName; } } // Use such objects as item identifiers String planets[] = {"Mercury", "Venus", "Earth", "Mars"}; for (int i=0; i<planets.length; i++) select.addItem(new PlanetId(planets[i])); ITEM_CAPTION_MODE_INDEX-
Index number of item is used as caption. This caption mode is applicable only to data sources that implement the
Container.Indexedinterface. If the interface is not available, the component will throw aClassCastException. TheSelectcomponent itself does not implement this interface, so the mode is not usable without a separate data source. AnIndexedContainer, for example, would work. ITEM_CAPTION_MODE_ITEM-
Stringrepresentation of item, acquired withtoString(), is used as the caption. This is applicable mainly when using a customItemclass, which also requires using a customContainerthat is used as a data source for theSelectcomponent. ITEM_CAPTION_MODE_PROPERTY-
Item captions are read from the
Stringrepresentation of the property with the identifier specified withsetItemCaptionPropertyId(). This is useful, for example, when you have a container that you use as the data source for aSelect, and you want to use a specific property for caption.In the example below, we bind a selection component to a bean container and use a property of the bean as the caption.
/* A bean with a "name" property. */ public class Planet implements Serializable { String name; public Planet(String name) { this.name = name; } public void setName(String name) { this.name = name; } public String getName() { return name; } } void propertyModeExample() { VerticalLayout layout = new VerticalLayout(); // Have a bean container to put the beans in BeanItemContainer<Planet> container = new BeanItemContainer<Planet>(Planet.class); // Put some example data in it container.addItem(new Planet("Mercury")); container.addItem(new Planet("Venus")); container.addItem(new Planet("Earth")); container.addItem(new Planet("Mars")); // Create a selection component bound to the container Select select = new Select("Planets", container); // Set the caption mode to read the caption directly // from the 'name' property of the bean select.setItemCaptionMode( Select.ITEM_CAPTION_MODE_PROPERTY); select.setItemCaptionPropertyId("name"); layout.addComponent(select);
A selection component provides the current selection as the property of the component (with the Property interface). The property value is an item identifier object that identifies the selected item. You can get the identifier with getValue() of the Property interface.
You can select an item with the corresponding setValue() method. In multiselect mode, the property will be an unmodifiable set of item identifiers. If no item is selected, the property will be null in single selection mode or an empty collection in multiselect mode.
The Select and NativeSelect components will show "-" selection when no actual item is selected. This is the null selection item identifier. You can set an alternative ID with setNullSelectionItemId(). Setting the alternative null ID is merely a visual text; the getValue() will still return null value if no item is selected, or an empty set in multiselect mode.
The item identifier of the currently selected item will be set as the property of the Select object. You can access it with the getValue() method of the Property interface of the component. Also, when handling changes in a Select component with the Property.ValueChangeListener interface, the Property.ValueChangeEvent will have the selected item as the property of the event, accessible with the getProperty() method.
The Select component allows, in single selection mode, selecting an item from a drop-down list. The component also has a text field area, which allows entering search text by which the items shown in the drop-down list are filtered.
In multiple selection mode, the component shows the items in a vertical list box, identical to ListSelect.
The Select component allows filtering the items available for selection. The component shows as an input box for entering text. The text entered in the input box is used for filtering the available items shown in a drop-down list. Pressing Enter will complete the item in the input box. Pressing Up- and Down-arrows can be used for selecting an item from the drop-down list. The drop-down list is paged and clicking on the scroll buttons will change to the next or previous page. The list selection can also be done with the arrow keys on the keyboard. The shown items are loaded from the server as needed, so the number of items held in the component can be quite large.
Vaadin provides two filtering modes: FILTERINGMODE_CONTAINS matches any item that contains the string given in the text field part of the component and FILTERINGMODE_STARTSWITH matches only items that begin with the given string. The filtering mode is set with setFilteringMode(). Setting the filtering mode to the default value FILTERINGMODE_OFF disables filtering.
Select select = new Select("Enter containing substring");
select.setFilteringMode(AbstractSelect.Filtering.FILTERINGMODE_CONTAINS);
/* Fill the component with some items. */
final String[] planets = new String[] {
"Mercury", "Venus", "Earth", "Mars",
"Jupiter", "Saturn", "Uranus", "Neptune" };
for (int i = 0; i < planets.length; i++)
for (int j = 0; j < planets.length; j++) {
select.addItem(planets[j] + " to " + planets[i]);
The above example uses the containment filter that matches to all items containing the input string. As shown in Figure 5.38, « Filtered Selection » below, when we type some text in the input area, the drop-down list will show all the matching items.
.v-filterselect { }
.v-filterselect-input { }
.v-filterselect-button { }
.v-filterselect-suggestpopup { }
.v-filterselect-prefpage-off { }
.v-filterselect-suggestmenu { }
.v-filterselect-status { }
.v-select { }
.v-select-select { }
In its default state, only the input field of the Select component is visible. The entire component is enclosed in v-filterselect style, the input field has v-filterselect-input style and the button in the right end that opens and closes the drop-down result list has v-filterselect-button style.
The drop-down result list has an overall v-filterselect-suggestpopup style. It contains the list of suggestions with v-filterselect-suggestmenu style and a status bar in the bottom with v-filterselect-status style. The list of suggestions is padded with an area with v-filterselect-prefpage-off style above and below the list.
In multiselect-mode, the styles of the component aere identical to ListSelect component, with v-select overall style and v-select-select for the native selection element.
The ListSelect component is list box that shows the selectable items in a vertical list. If the number of items exceeds the height of the component, a scrollbar is shown. The component allows both single and multiple selection modes, which you can set with setMultiSelect(). It is visually identical in both modes.
// Create the selection component
ListSelect select = new ListSelect("My Selection");
// Add some items
select.addItem("Mercury");
select.addItem("Venus");
select.addItem("Earth");
...
select.setNullSelectionAllowed(false);
// Show 5 items and a scrollbar if there are more
select.setRows(5);
The number of visible items is set with setRows().
NativeSelect offers the native selection component of web browsers, using the HTML <select> element. The component is shown as a drop-down list.
// Create the selection component
final NativeSelect select = new NativeSelect("Native Selection");
// Add some items
select.addItem("Mercury");
select.addItem("Venus");
...
// Set the width in "columns" as in TextField
select.setColumns(10);
select.setNullSelectionAllowed(false);
The setColumns() allows setting the width of the list as "columns", which is a measure that depends on the browser.
Multiple selection mode is not allowed; you should use the ListSelect component instead. Also adding new items, which would be enabled with setNewItemsAllowed(), is not allowed.
The OptionGroup class provides selection from alternatives using a group of radio buttons in single selection mode. In multiple selection mode, the items show up as check boxes.
OptionGroup optiongroup = new OptionGroup("My Option Group");
// Use the multiple selection mode.
myselect.setMultiSelect(true);
Figure 5.41, « Option Button Group in Single and Multiple Selection Mode » shows the OptionGroup in both single and multiple selection mode.
You can create check boxes individually using the CheckBox class, as described in Section 5.12, « CheckBox ». The advantages of the OptionGroup component are that as it maintains the individual check box objects, you can get an array of the currently selected items easily, and that you can easily change the appearance of a single component.
You can disable individual items in an OptionGroup with setItemEnabled(). The user can not select or deselect disabled items in multi-select mode, but in single-select mode the use can change the selection from a disabled to an enabled item. The selections can be changed programmatically regardless of whether an item is enabled or disabled. You can find out whether an item is enabled with isItemEnabled().
The setItemEnabled() identifies the item to be disabled by its item ID.
// Have an option group
OptionGroup group = new OptionGroup("My Disabled Group");
group.addItem("One");
group.addItem("Two");
group.addItem("Three");
// Disable one item
group.setItemEnabled("Two", false);
The item IDs are also used for the captions in this example. The result is shown in Figure 5.42, « OptionGroup with a Disabled Item ».
Setting an item as disabled turns on the v-disabled style for it.
.v-select-optiongroup {}
.v-select-option.v-checkbox {}
.v-select-option.v-radiobutton {}
The v-select-optiongroup is the overall style for the component. Each check box will have the v-checkbox style, borrowed from the CheckBox component, and each radio button the v-radiobutton style. Both the radio buttons and check boxes will also have the v-select-option style that allows styling regardless of the option type. Disabled items have additionally the v-disabled style.
The options are normally laid out vertically. You can use horizontal layout by setting display: inline-block for the options. The nowrap setting for the overall element prevents wrapping if there is not enough horizontal space in the layout, or if the horizontal width is undefined.
/* Lay the options horizontally */
.v-select-optiongroup-horizontal .v-select-option {
display: inline-block;
}
/* Avoid wrapping if the layout is too tight */
.v-select-optiongroup-horizontal {
white-space: nowrap;
}
/* Some extra spacing is needed */
.v-select-optiongroup-horizontal
.v-select-option.v-radiobutton {
padding-right: 10px;
}
Use of the above rules requires setting a custom horizontal style name for the component. The result is shown in Figure 5.43, « Horizontal OptionGroup ».
The TwinColSelect field provides a multiple selection component that shows two lists side by side, with the left column containing unselected items and the right column the selected items. The user can select items from the list on the left and click on the ">>" button to move them to the list on the right. Items can be deselected by selecting them in the right list and clicking on the "<<" button.
TwinColSelect is always in multi-select mode, so its property value is always a collection of the item IDs of the selected items, that is, the items in the right column.
The selection columns can have their own captions, separate from the overall component caption, which is managed by the containing layout. You can set the column captions with setLeftColumnCaption() and setRightColumnCaption().
 |
final TwinColSelect select =
new TwinColSelect("Select Targets to Destroy");
// Set the column captions (optional)
select.setLeftColumnCaption("These are left");
select.setRightColumnCaption("These are done for");
// Put some data in the select
String planets[] = {"Mercury", "Venus", "Earth", "Mars",
"Jupiter", "Saturn", "Uranus", "Neptune"};
for (int pl=0; pl<planets.length; pl++)
select.addItem(planets[pl]);
// Set the number of visible items
select.setRows(planets.length);
The resulting component is shown in Figure 5.44, « Twin Column Selection ».
The setRows() method sets the height of the component by the number of visible items in the selection boxes. Setting the height with setHeight() to a defined value overrides the rows setting.
.v-select-twincol {}
.v-select-twincol-options-caption {}
.v-select-twincol-selections-caption {}
.v-select-twincol-options {}
.v-select-twincol-buttons {}
.v-button {}
.v-button-wrap {}
.v-button-caption {}
.v-select-twincol-deco {}
.v-select-twincol-selections {}
The TwinColSelect component has an overall v-select-twincol style. If set, the left and right column captions have v-select-twincol-options-caption and v-select-twincol-options-caption style names, respectively. The left box, which displays the unselected items, has v-select-twincol-options-caption style and the right box, which displays the selected items, has v-select-twincol-options-selections style. Between them is the button area, which has overall v-select-twincol-buttons style; the actual buttons reuse the styles for the Button component. Between the buttons is a divider element with v-select-twincol-deco style.
The selection components allow the user to add new items, with a user interface similar to combo boxes in desktop user interfaces. You need to enable the newItemsAllowed mode with the setNewItemsAllowed() method.
myselect.setNewItemsAllowed(true);
The user interface for adding new items depends on the selection component and the selection mode. The regular Select component in single selection mode, which appears as a combo box, allows you to simply type the new item in the combo box and hit Enter to add it. In most other selection components, as well as in the multiple selection mode of the regular Select component, a text field that allows entering new items is shown below the selection list, and clicking the button will add the item in the list, as illustrated in Figure 5.45, « Select Component with Adding New Items Allowed ».
The identifier of an item added by the user will be a String object identical to the caption of the item. You should consider this if the item identifier of automatically filled items is some other type or otherwise not identical to the caption.
Adding new items is possible in both single and multiple selection modes and in all styles. Adding new items may not be possible if the Select is bound to an external Container that does not allow adding new items.
Setting the Select, NativeSelect, or OptionGroup components to multiple selection mode with the setMultiSelect() method changes their appearance to allow selecting multiple items.
SelectandNativeSelect-
These components appear as a native HTML selection list, as shown in Figure 5.45, « Select Component with Adding New Items Allowed ». By holding the Ctrl or Shift key pressed, the user can select multiple items.
OptionGroup- The option group, which is a radio button group in single selection mode, will show as a check box group in multiple selection mode. See Section 5.13.5, « Radio Button and Check Box Groups with
OptionGroup».
The TwinColSelect, described in Section 5.13.6, « Twin Column Selection with TwinColSelect », is a special multiple selection mode that is not meaningful for single selection.
myselect.setMultiSelect(true);
As in single selection mode, the selected items are set as the property of the Select object. In multiple selection mode, the property is a Collection of currently selected items. You can get and set the property with the getValue() and setValue() methods as usual.
A change in the selection will trigger a ValueChangeEvent, which you can handle with a Propery.ValueChangeListener. As usual, you should use setImmediate(true) to trigger the event immediately when the user changes the selection. The following example shows how to handle selection changes with a listener.
public class SelectExample
extends CustomComponent
implements Property.ValueChangeListener {
// Create a Select object with a caption.
Select select = new Select("This is a Select component");
VerticalLayout layout = new VerticalLayout();
Label status = new Label("-");
SelectExample () {
setCompositionRoot (layout);
layout.addComponent(select);
// Fill the component with some items.
final String[] planets = new String[] {
"Mercury", "Venus", "Earth", "Mars",
"Jupiter", "Saturn", "Uranus", "Neptune"};
for (int i=0; i<planets.length; i++)
select.addItem(planets[i]);
// By default, the change event is not triggered
// immediately when the selection changes.
// This enables the immediate events.
select.setImmediate(true);
// Listen for changes in the selection.
select.addListener(this);
layout.addComponent(status);
}
/* Respond to change in the selection. */
public void valueChange(Property.ValueChangeEvent event) {
// The event.getProperty() returns the Item ID (IID)
// of the currently selected item in the component.
status.setValue("Currently selected item ID: " +
event.getProperty());
}
}
You can set an icon for each item with setItemIcon(), or define an item property that provides the icon resource with setItemIconPropertyId(), in a fashion similar to captions. Notice, however, that icons are not supported in NativeSelect, TwinColSelect, and some other selection components and modes. This is because HTML does not support images inside the native select elements. Icons are also not really visually applicable.