Documentation

UI Components

UI Element

Both fields and buttons are "UI elements". The following types are provided:

Table 1. Fields
`UILabel`	Displaying of text
`UILink`	Hyperlink
`UITextField`	Field for single line text entry
`UITextArea`	Area for multiline text entry
`UIIntegerField`, `UIDoubleField`	Entry field for numbers
`UICheckbox`	Control for boolean input
`UIDateField`	Field for date entry with date picker
`UIComboBox`	Dropdown field with predefined options
`UIYesNoCombobox`	Dropdown field for boolean choices
`UIRadioButtons`	Radio buttons for selecting a single choice

Table 2. Buttons
`UIButton`	A button that triggers an action when clicked

The type of a field can be determined dynamically. This mechanism is called dynamic field.

Annotations for fields and buttons must exist on methods in a PMO class. The main difference between fields and buttons is that fields are used for displaying and editing of values and thus are bound to a value via data binding. Therefore annotations for fields must exist on a getter method of a PMO property. Only if domain model binding is used the method can be named differently.

Buttons are not bound to a value, but to an annotated method. It represents an executable action which is called by the button click.

Properties

All UI elements have the position property. In addition, many of the annotations have some aspects embedded, such as

label: String
enabled: boolean (not configurable for all elements)
visible: boolean
required: boolean (not configurable for all elements)

Fields have additional properties that are required for the domain model binding:

position must always be specified. For most annotations, label is also mandatory. All other properties have default values.

Position

The "position" property defines the order of elements in the UI. The relative size of the value is deciding. Elements with smaller position are added to a section first.

Gaps in the position numbering are allowed and common, to allow adding new UI elements at a later moment without needing to renumber all elements.

ModelObject and -Attribute: A field can be bound to an attribute of an existing model object using domain model binding. For this the properties modelAttribute and possibly modelObject are required. The function is described in the section names of model attributes.

UILabel

The annotation @UILabel generates an independent UI element displaying String content. In contrast to a deactivated UITextField its text is not framed by an input field. This annotation is equivalent to a com.vaadin.ui.Label.

The annotated method must return a value of String type. The return value defines what is shown as label.

A @UILabel also has the additional property label. If a value is set to it the text would appear beside the UILabel.
When used in a table, the label is used as the column name while the caption is displayed in the table cell.

HTML Content

The content of the label can be styled with HTML if htmlContent=true is specified.

Example HTML Label Content

    @UILabel(position = 5, label = "", htmlContent = true)
    public String getGender() {
        switch (contact.getGender()) {
            case FEMALE:
                return VaadinIcons.FEMALE.getHtml();
            case MALE:
                return VaadinIcons.MALE.getHtml();

            default:
                return VaadinIcons.CHILD.getHtml();
        }

    }

Styles: To style labels the property styleNames can be used to specify a list (actually a String[]) of CSS class names.

UILink

@UILink creates a hyperlink. In comparison to a button styled as a link, a link in Vaadin has the advantage that the user can use the context menu to follow the link in a separate browser tab or to copy the link. The caption can also be easily copied.

The annotated method should return the link URL as a string.

The annotation has the following attributes:

caption: String
captionType: CaptionType
target: String: Defines where to open the link as specified by HTML. The four predefined targets BLANK, SELF, PARENT and TOP can be found in the constant class LinkTarget as well as the empty String constant LinkTarget.DYNAMIC, which leads to dynamic target resolution via a get<PropertyName>Target method.

A @UILink also has the additional property label. If a value is set to it the text would appear beside the link.
When used in a table, the label is used as the column name while the caption is displayed as the link text in the table cell.

UICheckbox

@UICheckbox creates a com.vaadin.ui.CheckBox that is bound to a boolean property.

Instead of a label on the left side of the UI element, checkboxes usually have a caption on the right. This caption must be set with the property caption. If no caption is desired, an empty String must be set.

The usual label property is still available if any display text is needed on the left side additionally.
When used in a table, the label is used as the column name while the caption is displayed next to the checkbox in the table cell.

UITextField

A com.vaadin.ui.TextField for text entry. The annotation UITextfield has two additional properties:

maxLength: int
width: String

maxLength defines the maximum number of characters that can be entered or displayed in the field while width defines the visible width of the field using a number and a CSS unit, for example "5em" or "50%". This value is set to 100% by default which means it grabs the available space.

UITextArea

The annotation UITextArea corresponds to a com.vaadin.ui.TextArea. It is used for entering or displaying text that has more than one line.UITextArea has all the properties of the annotation UITextfield. In addition, it also has:

rows: int

The property rows defines the height of the UITextArea, not how many rows can be entered. Its default value is 1.

UIIntegerField and UIDoubleField

@UIIntegerfield and @UIDoubleField are text fields for displaying formatted numbers. Like @UITextField these annotations have the property maxLength.

The format can be defined with the property format: String, using the notation from java.text.NumberFormat.

If no format is specified for a UIIntegerField, linkki uses the default Java Integer NumberFormat (java.text.NumberFormat#getIntegerInstance(java.util.Locale)). In the case of UIDoubleField the format #,##0.00## is used by default. This format means that at least one digit is displayed before the decimal separator and two after, plus thousands separator. The documentation for the format definition can be looked up in the class java.text.DecimalFormat.

UIDateField

The annotation @UIDateField generates a date input field and corresponds to com.vaadin.ui.DateField. It allows specifying a date format using the property dateFormat: String. If not date format is defined the format matching the Locale setting is used. linkki uses "dd.MM.yyyy" by default for German. For other languages DateFormat.SHORT from the JDK is used. When the linkki widgetset is used, a MultiformatDateField is created instead. It allows multiple date formats to be set and by default uses the same date format as the standard Vaadin date field but also allows dates without punctuation to be entered, so that for example 010420 becomes 01.04.2020.

UIComboBox

A @UIComboBox allows selection of a value from a list. It has three additional properties:

    @UIComboBox(position = 20, label = "Model", modelAttribute = Car.PROPERTY_MODEL, required = RequiredType.REQUIRED_IF_ENABLED, content = AvailableValuesType.DYNAMIC, itemCaptionProvider = ToStringCaptionProvider.class)
    public void model() {
        /* model binding */
    }

Content

The attribute content defines which values are available:

Table 3. AvailableValuesType
`ENUM_VALUES_INCL_NULL`	the values of the combobox correspond to the values of the enum data type of the property, extended by the value `null` (default)
`ENUM_VALUES_EXCL_NULL`	the values of the combobox correspond to the values of the enum data type of the property
`DYNAMIC`	the values of the combobox are defined dynamically through the method `Collection<T> get<PropertyName>AvailableValues()`
`NO_VALUES`	this combobox has no selectable values

Width: The property width can be used to define the width of the combobox using CSS syntax (e.g. "25em" or "100%"). The default value is -1px, corresponding to the standard size given by Vaadin.

ItemCaptionProvider

For displaying the individual values in the combobox a org.linkki.core.defaults.ui.element.ItemCaptionProvider<T> is used. By default it is a DefaultCaptionProvider that expects a method getName(). Via the property itemCaptionProvider an alternative implementation class can be specified. linkki offers two additional ones:

ToStringCaptionProvider: uses the `toString()`method of the elements
IdAndNameCaptionProvider: displays name and ID in the format "name [ID]" using the methods getName() and getId().

UIYesNoComboBox

A @UIYesNoComboBox allows selection of a boolean value from a dropdown list like a UIComboBox. The difference is that the values are not a generic enumeration or list but the well known boolean values true and false (and for Boolean, the option null). It has two properties known from the UIComboBox:

width: String
itemCaptionProvider: Class<? extends ItemCaptionProvider<?>> with a default implementation BooleanCaptionProvider that uses common names in the current locale like "Yes"/"No" or "Ja"/"Nein".

UIRadioButtons

@UIRadioButtons allow selection of a single value using a group of buttons. Multiple values cannot be selected at the same time.

content: AvailableValuesType
itemCaptionProvider: Class<? extends ItemCaptionProvider<?>> with a default implementation DefaultCaptionProvider that delegates to getName or toString
buttonAlignment: AlignmentType

UISubsetChooser

For selection of multiple values from a list, linkki offers the @UISubsetChooser. In this UI control elements are selected by moving them from a list on the left to a list on the right. The display of the individual elements is similar to UIComboBox, but with a default of ToStringCaptionProvider. As with UICombobox the width can be defined via the property width.

The content of a subset chooser must be specified with the method Collection<T> get<PropertyName>AvailableValues(). The bound property must be of type Set<T>.

The caption of both columns can be set through the properties leftColumnCaption: String and rightColumnCaption: String.

UICustomField

Other controls can also easily be generated and bound by linkki. For this the annotation @UICustomField is used.

The control class is specified with the property uiControl: Class<? extends Field<?>>. If the control implements com.vaadin.data.HasItems<T> the values can be defined by content: AvailableValuesType like with UIComboBox.

@UICustomField only supports controls with a parameter-less constructor.

UICustomField Example: PasswordField

    @UICustomField(position = 20, label = "Password", required = RequiredType.REQUIRED, modelAttribute = User.PROPERTY_PASSWORD, uiControl = PasswordField.class)
    public void password() {
        // model binding
    }

Dynamic Field

linkki allows for dynamic typing of an input field. In the following example Retention should only be freely writable if CarType is set to STANDARD. Otherwise the user can only select values from a list:

    @UIDoubleField(position = 30, label = "Retention", modelAttribute = Car.PROPERTY_RETENTION, required = RequiredType.REQUIRED_IF_ENABLED)
    @UIComboBox(position = 30, label = "Retention", modelAttribute = Car.PROPERTY_RETENTION, required = RequiredType.REQUIRED_IF_ENABLED, content = AvailableValuesType.DYNAMIC, itemCaptionProvider = RetentionCaptionProvider.class)
    public void retention() {
        /* model binding */
    }

    public List<Double> getRetentionAvailableValues() {
        return Arrays.asList(2_000.0, 5_000.0, 10_000.0);
    }

    public Class<?> getRetentionComponentType() {
        return car.getCarType() == CarType.STANDARD ? UIDoubleField.class : UIComboBox.class;
    }

The selectable UI elements are defined via annotations on the method, as is customary. They must, however, fulfill the following requirements, to allow the type to be determined dynamically:

the position in the UI* annotations must match
the label must have the same value

If the position values are identical but the label values differ, an exception is thrown.

Which UI element is displayed for each PMO instance is determined by the method Class<?> get<PropertyName>ComponentType(). It returns the class of the UI*-Annotation for the UI control to be rendered.

UIButton

The annotation @UIButton is used to mark the method that should be executed with the click on the button.

Buttons are not bound to values. Since buttons therefore have no corresponding PMO property, the name of the annotated method is used to determine the associated methods. The behavior is similar to the domain model binding, although buttons have no property modelAttribute.

    @UIButton(position = 10, showIcon = true, icon = VaadinIcons.CHECK_SQUARE_O, //
            captionType = CaptionType.NONE, enabled = EnabledType.DYNAMIC, //
            shortcutKeyCode = KeyCode.ENTER, styleNames = ValoTheme.BUTTON_PRIMARY)
    public void save() {
        saveAction.apply();
    }

    public boolean isSaveEnabled() {
        return canSaveSupplier.getAsBoolean();
    }

    @UIButton(position = 20, captionType = CaptionType.STATIC, caption = "reset", styleNames = ValoTheme.BUTTON_LINK)
    public void reset() {
        resetAction.apply();
    }

Apart from the common properties, buttons have these additional ones:

Caption

The text shown on a button is called a caption. It is not to be confused with a Label, which usually appears besides the control. A button can have both a caption and a label text.

captionType: CaptionType

Table 4. CaptionType
`STATIC`	the caption of the button is read from the attribute `caption` (default)
`NONE`	the button has no caption
`DYNAMIC`	the caption of the button is determined by the return value of the method `String get<PropertyName>Caption()`. The value of the attribute `caption` is ignored.

Icon

Apart from captions, buttons can be adorned with icons. For this the constants of the Vaadin class VaadinIcons are used. For the icon to be displayed the property showIcon must be set true.

Style Names

Depending on the function buttons must be styled differently. A typical example for this is the link button, a button that looks like a link. For this purpose the annotation @UIButton has the property styleNames. The value of this property are the CSS class names that should apply to the button.

Key Bindings

Some buttons shouldn’t be triggered only by mouse click, but also by key combinations. These can be specified with the properties shortcutModifierKeys and shortcutKeyCode. shortcutModifierKeys defines which keys must be pressed and held before the key in the shortcutKeyCode is pressed. For instance, in many applications saving is triggered with the shortcut combination "Ctrl + s". In this case the "Ctrl" key is the modifier and the "s" key is the shortcut key.

In both properties individual keys are identified by integer values. The appropriate value for each key can be found in the Vaadin classes ModifierKey and KeyCode.