vaadin-framework/client/src/main/java/com/vaadin/client/renderers/ClickableRenderer.java

/*
 * Copyright 2000-2016 Vaadin Ltd.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package com.vaadin.client.renderers;

import com.google.gwt.dom.client.BrowserEvents;
import com.google.gwt.dom.client.Element;
import com.google.gwt.dom.client.EventTarget;
import com.google.gwt.event.dom.client.ClickEvent;
import com.google.gwt.event.dom.client.ClickHandler;
import com.google.gwt.event.dom.client.DomEvent;
import com.google.gwt.event.dom.client.MouseEvent;
import com.google.gwt.event.shared.EventHandler;
import com.google.gwt.event.shared.HandlerManager;
import com.google.gwt.event.shared.HandlerRegistration;
import com.google.gwt.user.client.ui.Composite;
import com.google.gwt.user.client.ui.Widget;
import com.vaadin.client.WidgetUtil;
import com.vaadin.client.widget.escalator.Cell;
import com.vaadin.client.widget.escalator.RowContainer;
import com.vaadin.client.widget.grid.CellReference;
import com.vaadin.client.widget.grid.EventCellReference;
import com.vaadin.client.widgets.Escalator;
import com.vaadin.client.widgets.Grid;
import com.vaadin.shared.ui.grid.GridConstants.Section;

/**
 * An abstract superclass for renderers that render clickable widgets. Click
 * handlers can be added to a renderer to listen to click events emitted by all
 * widgets rendered by the renderer.
 *
 * @param <T>
 *            the presentation (column) type
 * @param <W>
 *            the widget type
 *
 * @since 7.4
 * @author Vaadin Ltd
 */
public abstract class ClickableRenderer<T, W extends Widget>
        extends WidgetRenderer<T, W> implements ClickHandler {

    /**
     * A handler for {@link RendererClickEvent renderer click events}.
     *
     * @param <R>
     *            the row type of the containing Grid
     *
     * @see ButtonRenderer#addClickHandler(RendererClickHandler)
     */
    public interface RendererClickHandler<R> extends EventHandler {

        /**
         * Called when a rendered button is clicked.
         *
         * @param event
         *            the event representing the click
         */
        void onClick(RendererClickEvent<R> event);
    }

    /**
     * An event fired when a widget rendered by a ClickableWidgetRenderer
     * subclass is clicked.
     *
     * @param <R>
     *            the row type of the containing Grid
     */
    @SuppressWarnings("rawtypes")
    public static class RendererClickEvent<R>
            extends MouseEvent<RendererClickHandler> {

        @SuppressWarnings("unchecked")
        static final Type<RendererClickHandler> TYPE = new Type<RendererClickHandler>(
                BrowserEvents.CLICK, new RendererClickEvent());

        private CellReference<R> cell;

        private R row;

        private RendererClickEvent() {
        }

        /**
         * Returns the cell of the clicked button.
         *
         * @return the cell
         */
        public CellReference<R> getCell() {
            return cell;
        }

        /**
         * Returns the data object corresponding to the row of the clicked
         * button.
         *
         * @return the row data object
         */
        public R getRow() {
            return row;
        }

        @Override
        public Type<RendererClickHandler> getAssociatedType() {
            return TYPE;
        }

        @Override
        @SuppressWarnings("unchecked")
        protected void dispatch(RendererClickHandler handler) {

            EventTarget target = getNativeEvent().getEventTarget();

            if (!Element.is(target)) {
                return;
            }

            Element e = Element.as(target);
            Grid<R> grid = (Grid<R>) findClosestParentGrid(e);

            cell = findCell(grid, e);
            row = cell.getRow();

            handler.onClick(this);
        }

        /**
         * Returns the cell the given element belongs to.
         *
         * @param grid
         *            the grid instance that is queried
         * @param e
         *            a cell element or the descendant of one
         * @return the cell or null if the element is not a grid cell or a
         *         descendant of one
         */
        private static <T> CellReference<T> findCell(Grid<T> grid, Element e) {
            RowContainer container = getEscalator(grid).findRowContainer(e);
            if (container == null) {
                return null;
            }
            Cell cell = container.getCell(e);
            EventCellReference<T> cellReference = new EventCellReference<>(
                    grid);
            // FIXME: Section is currently always body. Might be useful for the
            // future to have an actual check.
            cellReference.set(cell, Section.BODY);
            return cellReference;
        }

        private native static Escalator getEscalator(Grid<?> grid)
        /*-{
          return grid.@com.vaadin.client.widgets.Grid::escalator;
        }-*/;

        /**
         * Returns the Grid instance containing the given element, if any.
         * <p>
         * <strong>Note:</strong> This method may not work reliably if the grid
         * in question is wrapped in a {@link Composite} <em>unless</em> the
         * element is inside another widget that is a child of the wrapped grid;
         * please refer to the note in
         * {@link WidgetUtil#findWidget(Element, Class) Util.findWidget} for
         * details.
         *
         * @param e
         *            the element whose parent grid to find
         * @return the parent grid or null if none found.
         */
        private static Grid<?> findClosestParentGrid(Element e) {
            Widget w = WidgetUtil.findWidget(e, null);

            while (w != null && !(w instanceof Grid)) {
                w = w.getParent();
            }
            return (Grid<?>) w;
        }
    }

    private HandlerManager handlerManager;

    /**
     * {@inheritDoc}
     * <p>
     * <em>Implementation note:</em> It is the implementing method's
     * responsibility to add {@code this} as a click handler of the returned
     * widget, or a widget nested therein, in order to make click events
     * propagate properly to handlers registered via
     * {@link #addClickHandler(RendererClickHandler) addClickHandler}.
     */
    @Override
    public abstract W createWidget();

    /**
     * Adds a click handler to this button renderer. The handler is invoked
     * every time one of the widgets rendered by this renderer is clicked.
     * <p>
     * Note that the row type of the click handler must match the row type of
     * the containing Grid.
     *
     * @param handler
     *            the click handler to be added
     */
    public HandlerRegistration addClickHandler(
            RendererClickHandler<?> handler) {
        if (handlerManager == null) {
            handlerManager = new HandlerManager(this);
        }
        return handlerManager.addHandler(RendererClickEvent.TYPE, handler);
    }

    @Override
    public void onClick(ClickEvent event) {
        /*
         * The handler manager is lazily instantiated so it's null iff
         * addClickHandler is never called.
         */
        if (handlerManager != null) {
            DomEvent.fireNativeEvent(event.getNativeEvent(), handlerManager);
        }
    }
}