SaveStateManager.java

/*
 * Copyright (C) 2012 The Android Open Source Project
 *
 * 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.motorolamobility.studio.android.db.core.ui.view;

import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

import org.eclipse.core.runtime.preferences.IEclipsePreferences;
import org.eclipse.core.runtime.preferences.InstanceScope;

import com.motorolamobility.studio.android.db.core.DbCoreActivator;
import com.motorolamobility.studio.android.db.core.ui.ISaveStateTreeNode;

/**
 * Manager class responsible to handle save state for tree nodes.
 * Note: The saveState method will be called only after workbench quits, quiting the view will not fire the save event state.
 * This class is a singleton.
 * Users must register the ISaveStateTreenode by using resiterSaveStateNode method.
 * Don't forget to unregister the node if node is removed.
 */
public class SaveStateManager
{

    private static SaveStateManager instance;

    private final Set<ISaveStateTreeNode> registeredTreeNodes;

    private final IEclipsePreferences prefNode;

    /*
     * Private constructor, this is a singleton.
     */
    private SaveStateManager()
    {
        registeredTreeNodes = Collections.synchronizedSet(new HashSet<ISaveStateTreeNode>());
        prefNode = InstanceScope.INSTANCE.getNode(DbCoreActivator.PLUGIN_ID);
    }

    /**
     * @return the single instance of {@link SaveStateManager}
     */
    public static SaveStateManager getInstance()
    {
        if (instance == null)
        {
            instance = new SaveStateManager();
        }

        return instance;
    }

    /**
     * Register a node to be saved.
     * @param treeNode to be asked for save
     */
    public void registerSaveStateNode(ISaveStateTreeNode treeNode)
    {
        synchronized (registeredTreeNodes)
        {
            registeredTreeNodes.add(treeNode);
        }
    }

    /**
     * Calls the saveState method for all registered nodes.
     * @param memento
     */
    public void saveState()
    {
        synchronized (registeredTreeNodes)
        {
            for (ISaveStateTreeNode registeredTreeNode : registeredTreeNodes)
            {
                registeredTreeNode.saveState(prefNode);
            }
        }
    }

    /**
     * Unregister the given node from this manager.
     * @param node
     */
    public void unregisterSaveStateNode(ISaveStateTreeNode node)
    {
        synchronized (registeredTreeNodes)
        {
            registeredTreeNodes.remove(node);
        }
    }

    /**
     * Retrieves the {@link IEclipsePreferences} prefNode.
     * @return The {@link IEclipsePreferences} node used bu this manager to save the states.
     */
    public IEclipsePreferences getPrefNode()
    {
        return prefNode;
    }
}