Creating a dynamic element

Dynamic elements are stateless: one instance serves every render of a template. Keep bindings in fields set by the constructor, and nothing else. Need state? Write a component.

A simple element

public class CurrentYear extends NGDynamicElement {

	public CurrentYear( String name, Map<String, NGAssociation> associations, NGElement contentTemplate ) {
		super( null, null, null );
	}

	@Override
	public void appendToResponse( NGResponse response, NGContext context ) {
		response.appendContentString( String.valueOf( Year.now().getValue() ) );
	}
}

&copy; <wo:CurrentYear />

• The constructor signature is required, and it must call super( null, null, null ).
• Put the class in your app's package or its components subpackage, and use it by its simple class name.

With bindings and content

Extend NGDynamicGroup to render content between the tags:

public class Note extends NGDynamicGroup {

	private final NGAssociation _important;

	public Note( String name, Map<String, NGAssociation> associations, NGElement contentTemplate ) {
		super( name, associations, contentTemplate );
		_important = associations.get( "important" );
	}

	@Override
	public void appendToResponse( NGResponse response, NGContext context ) {
		final boolean important = _important != null
				&& _important.booleanValueInComponent( context.component() );

		response.appendContentString( important ? "<aside class=\"note important\">" : "<aside class=\"note\">" );
		appendChildrenToResponse( response, context );
		response.appendContentString( "</aside>" );
	}
}

<wo:Note important="$true">Back up first.</wo:Note>

• Read values with association.valueInComponent( context.component() ), and set them with setValue( value, component ).
• For a missing required binding, throw NGBindingConfigurationException from the constructor. It shows as an error box in the page.
• Truthiness: only null, false and 0 are false.

Actions and forms

Override takeValuesFromRequest and invokeAction too, as NGHyperlink and NGTextField do. Groups pass them on with takeChildrenValuesFromRequest and invokeChildrenAction. (TODO: example.)