com.google.gwt.event.logical.shared.BeforeSelectionEvent.java Source code

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Here is the source code for com.google.gwt.event.logical.shared.BeforeSelectionEvent.java

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/*
 * Copyright 2008 Google Inc.
 * 
 * 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.google.gwt.event.logical.shared;

import com.google.gwt.event.shared.GwtEvent;

/**
 * Represents a before selection event.
 * 
 * @param <T> the type about to be selected
 */
public class BeforeSelectionEvent<T> extends GwtEvent<BeforeSelectionHandler<T>> {

    /**
     * Handler type.
     */
    private static Type<BeforeSelectionHandler<?>> TYPE;

    /**
     * Fires a before selection event on all registered handlers in the handler
     * manager. If no such handlers exist, this method will do nothing.
     * 
     * @param <T> the item type
     * @param source the source of the handlers
     * @param item the item
     * @return the event so that the caller can check if it was canceled, or null
     *         if no handlers of this event type have been registered
     */
    public static <T> BeforeSelectionEvent<T> fire(HasBeforeSelectionHandlers<T> source, T item) {
        // If no handlers exist, then type can be null.
        if (TYPE != null) {
            BeforeSelectionEvent<T> event = new BeforeSelectionEvent<T>();
            event.setItem(item);
            source.fireEvent(event);
            return event;
        }
        return null;
    }

    /**
     * Gets the type associated with this event.
     * 
     * @return returns the handler type
     */
    public static Type<BeforeSelectionHandler<?>> getType() {
        if (TYPE == null) {
            TYPE = new Type<BeforeSelectionHandler<?>>();
        }
        return TYPE;
    }

    private T item;

    private boolean canceled;

    /**
     * Creates a new before selection event.
     */
    protected BeforeSelectionEvent() {
    }

    /**
     * Cancel the before selection event.
     * 
     * Classes overriding this method should still call super.cancel().
     */
    public void cancel() {
        canceled = true;
    }

    // The instance knows its BeforeSelectionHandler is of type I, but the TYPE
    // field itself does not, so we have to do an unsafe cast here.
    @SuppressWarnings("unchecked")
    @Override
    public final Type<BeforeSelectionHandler<T>> getAssociatedType() {
        return (Type) TYPE;
    }

    /**
     * Gets the item.
     * 
     * @return the item
     */
    public T getItem() {
        return item;
    }

    /**
     * Has the selection event already been canceled?
     * 
     * @return is canceled
     */
    public boolean isCanceled() {
        return canceled;
    }

    @Override
    protected void dispatch(BeforeSelectionHandler<T> handler) {
        handler.onBeforeSelection(this);
    }

    /**
     * Sets the item.
     * 
     * @param item the item
     */
    protected final void setItem(T item) {
        this.item = item;
    }
}