Dropdown Button

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The Dropdown Button lets the operator choose one option from a list. The button shows the selected option; a click opens the list. It is found in the Input - OpenBridge section of the Perspective Component Palette as Dropdown Button.

1. Label of the selected option — see Options.
2. Arrow that shows that the button opens a list.

The Dropdown Button is one of the input components. Values, events, disabling and the behavior in the Designer are shared by all of them and are described in Input Components — Common Features. This page covers what is specific to the Dropdown Button.

A Dropdown Button with default properties:

A new Dropdown Button has no options and shows only the arrow. Add the options first.

Note: The list does not open in the Designer, not even in Preview Mode: the Designer’s built-in browser cannot show this kind of list. Try the component in a session. To choose what it shows in the Designer, set value in the property editor.

Options

options is the list to choose from. Each option has a label, which is the text the operator sees, and a value, which is what is written to the value property when the option is chosen:

[
  {"label": "Auto", "value": "auto"},
  {"label": "Manual", "value": "manual"},
  {"label": "Off", "value": "off"}
]

A click on the button opens the list:

The list is drawn by the browser, so its look differs somewhat between browsers and devices; on a phone or a tablet it is the selection list of that device.

Give every option a different value. An option value can be a text, a number or true/false.

Properties

Name	Description	Property Type
options	The options to choose from. Empty by default.	array
options[].label	Text shown for the option.	value
options[].value	Value written to value when the option is chosen.	value

---

Value

value is the value of the selected option. The button shows the label of that option.

When the operator chooses another option, the component writes the value of that option to value and then fires onActionPerformed once. Bind value bidirectionally to a tag to let the operator set the tag; see Values.

The value is written with the type it looks like: choosing an option with the value 2 writes the number 2, and true or false writes a boolean. Anything else is written as text.

A Value That Is Not an Option

When value does not match any option — for instance while it is empty — what is shown depends on allowEmptySelection:

allowEmptySelection	Shown	Image
false (default)	The first option. Here value is standby, which is not in the list.
true	Nothing: the button is empty until the operator chooses an option.

Note: With allowEmptySelection at false the first option is only shown. It is not written to value, which keeps the value it had until the operator chooses an option.

Properties

Name	Description	Property Type
value	Value of the selected option. Written when the operator chooses. Empty by default.	value
allowEmptySelection	Show an empty button instead of the first option when value is not an option. Default false.	value

---

Width

The button is as wide as the label of the selected option needs, so its width changes with the selection. Set fullWidth to true to make it fill the width of the component instead. The blue frame in the images is the component’s box:

fullWidth = false	fullWidth = true

Properties

Name	Description	Property Type
fullWidth	Make the button fill the width of the component. Default false.	value

---

Integration Style

Set integration to true when the button is placed on an integration bar. It is then drawn without a border, in the colours of that bar:

Properties

Name	Description	Property Type
integration	Draw the button for use on an integration bar. Default false.	value

---

Disabled

A disabled Dropdown Button does not open its list. See Disabled for the disabled property, which works in the same way on every input component.

Common Properties

• Appearance — style.

Component Events

Event	Description	Event Object
onActionPerformed	Fired when the operator chooses another option, after value has been written.	—

See Events.

Examples

Example 1 — Control Mode

1. Drop a Dropdown Button into the view.

2. Set options to:

   [
     {"label": "Auto", "value": "auto"},
     {"label": "Manual", "value": "manual"},
     {"label": "Off", "value": "off"}
   ]

3. Bind value to the tag [default]Pump01/Mode and enable Bidirectional.

4. Set fullWidth to true so that the button keeps its width when the selection changes.

Example 2 — Numeric Values

1. Set options to a list with numbers as values:

   [
     {"label": "Low", "value": 1},
     {"label": "Medium", "value": 2},
     {"label": "High", "value": 3}
   ]

2. Bind value bidirectionally to an integer tag, for example [default]Fan01/SpeedStep. Choosing Medium writes the number 2 to the tag.