MaterialDropdown.java

public class MaterialDropDown extends UnorderedList implements Loader, HasConfiguration, HasSelectionHandlers<Widget>, HasInOutDurationTransition {

    private int inDuration = 300;
    private int outDuration = 225;
    private int gutter = 0;
    private boolean constrainWidth = true;
    private boolean hover = false;
    private boolean belowOrigin = false;
    private Alignment alignment = Alignment.LEFT;
    private List<Widget> children = new ArrayList<>();
    private String activator;
    private Element activatorElement;
    private JsDropdownOptions options;

    public MaterialDropDown() {
        setInitialClasses(CssName.DROPDOWN_CONTENT);
        setId(DOM.createUniqueId());
    }

    /**
     * Add a list item selection when button, link, icon button pressed.
     *
     * @param activator data-activates attribute name of your dropdown activator.
     */
    @UiConstructor
    public MaterialDropDown(String activator) {
        this();
        this.activator = activator;
        getElement().setId(this.activator);
    }

    public MaterialDropDown(Element activatorElement) {
        this();
        activatorElement.setAttribute("data-activates", getId());
        this.activatorElement = activatorElement;
    }

    public MaterialDropDown(UIObject activator) {
        this(activator.getElement());
    }

    @Override
    protected void onLoad() {
        super.onLoad();

        Widget parent = getParent();
        if (parent instanceof HasActivates) {
            String uid = DOM.createUniqueId();
            ((HasActivates) parent).setActivates(uid);
            setId(uid);
            activatorElement = parent.getElement();
        } else if (activatorElement == null) {
            activatorElement = DOMHelper.getElementByAttribute("data-activates", activator);
            if (activatorElement == null) {
                GWT.log("There is no activator element with id: '" + activator + "' in the DOM, " +
                        "cannot instantiate MaterialDropDown without a data-activates.", new IllegalStateException());
            }
        }

        configure();
        load();
    }

    @Override
    public void configure() { 
        options = new JsDropdownOptions();
        options.constrain_width = constrainWidth;
        options.inDuration = inDuration;
        options.outDuration = outDuration;
        options.hover = hover;
        options.gutter = gutter;
        options.belowOrigin = belowOrigin;
        options.alignment = alignment.getCssName();

    }

    @Override
    public void load() {
        $(activator).dropdown(options);
        setupActivator();
    }

    @Override
    public void reload() {
        remove(activatorElement);
        configure();
    }

    @Override
    public void add(final Widget child) {
        String tagName = child.getElement().getTagName();
        if (child instanceof ListItem || tagName.toLowerCase().startsWith("li")) {
            child.getElement().getStyle().setDisplay(Style.Display.BLOCK);
            add(child, (Element) getElement());
        } else {
            ListItem li = new ListItem(child);
            children.add(child);
            registerHandler(child.addDomHandler(event -> SelectionEvent.fire(MaterialDropDown.this, child), ClickEvent.getType()));

            // Checks if there are sub dropdown components

            if (child instanceof MaterialLink) {
                MaterialLink link = (MaterialLink) child;
                for (int i = 0; i < link.getWidgetCount(); i++) {
                    if (link.getWidget(i) instanceof MaterialDropDown) {
                        link.addClickHandler(DomEvent::stopPropagation);
                        link.stopTouchStartEvent();
                    }
                }
            }

            if (child instanceof HasWaves) {
                li.setWaves(((HasWaves) child).getWaves());
                ((HasWaves) child).setWaves(null);
            }
            li.getElement().getStyle().setDisplay(Style.Display.BLOCK);
            add(li, (Element) getElement());
        }
    }

    protected void remove(Element activator) {
        $(activator).dropdown("remove");
    }

    @Override
    public void setInDuration(int durationMillis) {
        this.inDuration = durationMillis;
    }

    @Override
    public int getInDuration() {
        return inDuration;
    }

    @Override
    public void setOutDuration(int durationMillis) {
        this.outDuration = durationMillis;
    }

    @Override
    public int getOutDuration() {
        return outDuration;
    }

    /**
     * If true, constrainWidth to the size of the dropdown activator. Default: true
     */
    public void setConstrainWidth(boolean constrainWidth) {
        this.constrainWidth = constrainWidth;
    }

    public boolean isConstrainWidth() {
        return constrainWidth;
    }

    /**
     * If true, the dropdown will open on hover. Default: false
     */
    public void setHover(boolean hover) {
        this.hover = hover;
    }

    public boolean isHover() {
        return hover;
    }

    /**
     * This defines the spacing from the aligned edge. Default: 0
     */
    public void setGutter(int gutter) {
        this.gutter = gutter;
    }

    public int getGutter() {
        return gutter;
    }

    /**
     * If true, the dropdown will show below the activator. Default: false
     */
    public void setBelowOrigin(boolean belowOrigin) {
        this.belowOrigin = belowOrigin;
    }

    public boolean isBelowOrigin() {
        return belowOrigin;
    }

    /**
     * Defines the edge the menu is aligned to. Default: 'left'
     */
    public void setAlignment(Alignment alignment) {
        this.alignment = alignment;
    }

    public Alignment getAlignment() {
        return alignment;
    }

    /**
     * Get the unique activator set by material widget e.g links, icons, buttons to trigger the dropdown.
     */
    public String getActivator() {
        return activator;
    }

    /**
     * Set the unique activator of each dropdown component and it must be unique
     */
    public void setActivator(String activator) {
        this.activator = activator;
        setId(activator);
    }

    @Override
    public void setEnabled(boolean enabled) {
        super.setEnabled(enabled);
        reload();
    }

    protected void setupActivator() {
        Widget parent = getParent();
        if (parent instanceof HasEnabled) {
            ((HasEnabled) parent).setEnabled(isEnabled());
        }
    }

    public List<Widget> getItems() {
        return children;
    }

    public Element getActivatorElement() {
        return activatorElement;
    }

    @Override
    public HandlerRegistration addSelectionHandler(final SelectionHandler<Widget> handler) {
        return addHandler(new SelectionHandler<Widget>() {
            @Override
            public void onSelection(SelectionEvent<Widget> event) {
                Widget widget = event.getSelectedItem();
                if (widget instanceof HasEnabled) {
                    if (((HasEnabled) widget).isEnabled() && isEnabled()) {
                        handler.onSelection(event);
                    }
                }
            }
        }, SelectionEvent.getType());
    }
}