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UI Placeholder and Enclosure

UI Placeholder and Enclosure#

This pages explains how to write Enclosure and Placeholder. Enclosure and Placeholder are component which are displayed or hidden (at page-generation level) based on various input variables.

Conditions and component’s visibility#

Igloo provides Condition base class which provides easy-to-use transformation of a Condition (that resolves to true or false result on an applies method’s call) as an enclosure or placeholder behavior.

Once your Condition created, you can generate the following behaviors :

  • thenShow(): behavior that sets visibilityAllowed property equal to condition’s result (enclosure-like behavior)

  • thenHide(): behavior that sets visibilityAllowed property equal to negated condition’s result (placeholder-like behavior)

  • thenShowInternal(): behavior that sets visible property equal to condition’s result

  • thenHideInternal(): behavior that sets visible property equal to negated condition’s result

By convention, visibilityAllowed setting (thenHide(), thenShow()) must be preferred for external impact on component visibility (permission, inter-component dependencies driven by application behaviors).

On the contrary, visible setting is used for internal behaviors. For example, for a table + pager widget, to control the pager’s visibility in relation to result’s page number, as this behavior is driven by an internal state of the component.

To circumvent visibility settings when visible and visibilityAllowed properties conflict, use of an intermediate component may be a solution.

Component’s enabled property#

thenEnable() and thenDisable() methods are provided to allow enabled property control, based on the same mechanism than visibility control.

Deprecated patterns#

Before Condition, the following components and behaviors were provided:

  • PlaceholderBehavior, EnclosureBehavior: sets visibilityAllowed property (by default) or an alternate property when provided. This behavior can be replaced by a Condition method call:

    • .add(new PlaceholderBehavior().component(component)): .add(Condition.componentVisible(component).thenHide())

    • .add(new EnclosureBehavior().component(component)): .add(Condition.componentVisible(component).thenShow())

    • .add(new PlaceholderBehavior(ComponentBooleanProperty.VISIBLE).component(component)): .add(Condition.componentVisible(component).thenHideInternal())

    • .add(new EnclosureBehavior(ComponentBooleanProperty.VISIBLE).component(component)): .add(Condition.componentVisible(component).thenShowInternal())

When other method than component() is used on ...Behavior object, others Condition’s methods or subclasses can be used to provides the right behavior (permission(), anyPermission(), role(), isTrue(), isFalse(), predicate(), …)

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