com.google.gwt.view.client.SingleSelectionModel.java Source code

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Here is the source code for com.google.gwt.view.client.SingleSelectionModel.java

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/*
 * Copyright 2010 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.view.client;

import com.google.gwt.view.client.SelectionModel.AbstractSelectionModel;

/**
 * A simple selection model that allows only one object to be selected a a time.
 *
 * @param <T> the record data type
 */
public class SingleSelectionModel<T> extends AbstractSelectionModel<T> {

    private Object curKey;
    private T curSelection;

    // Pending selection change
    private boolean newSelected;
    private T newSelectedObject = null;
    private boolean newSelectedPending;

    /**
     * Constructs a SingleSelectionModel without a key provider.
     */
    public SingleSelectionModel() {
        super(null);
    }

    /**
     * Constructs a SingleSelectionModel with the given key provider.
     *
     * @param keyProvider an instance of ProvidesKey<T>, or null if the record
     *        object should act as its own key
     */
    public SingleSelectionModel(ProvidesKey<T> keyProvider) {
        super(keyProvider);
    }

    /**
     * Gets the currently-selected object.
     *
     * @return the selected object
     */
    public T getSelectedObject() {
        resolveChanges();
        return curSelection;
    }

    public boolean isSelected(T object) {
        resolveChanges();
        if (curSelection == null || curKey == null || object == null) {
            return false;
        }
        return curKey.equals(getKey(object));
    }

    public void setSelected(T object, boolean selected) {
        // If we are deselecting a value that isn't actually selected, ignore it.
        if (!selected) {
            Object oldKey = newSelectedPending ? getKey(newSelectedObject) : curKey;
            Object newKey = getKey(object);
            if (!equalsOrBothNull(oldKey, newKey)) {
                return;
            }
        }
        newSelectedObject = object;
        newSelected = selected;
        newSelectedPending = true;
        scheduleSelectionChangeEvent();
    }

    @Override
    protected void fireSelectionChangeEvent() {
        if (isEventScheduled()) {
            setEventCancelled(true);
        }
        resolveChanges();
    }

    private boolean equalsOrBothNull(Object a, Object b) {
        return (a == null) ? (b == null) : a.equals(b);
    }

    private void resolveChanges() {
        if (!newSelectedPending) {
            return;
        }

        Object key = getKey(newSelectedObject);
        boolean sameKey = equalsOrBothNull(curKey, key);
        boolean changed = false;
        if (newSelected) {
            changed = !sameKey;
            curSelection = newSelectedObject;
            curKey = key;
        } else if (sameKey) {
            changed = true;
            curSelection = null;
            curKey = null;
        }

        newSelectedObject = null;
        newSelectedPending = false;

        // Fire a selection change event.
        if (changed) {
            SelectionChangeEvent.fire(this);
        }
    }
}