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/*
 * Copyright © 1996-2009 GlobalMentor, 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.globalmentor.swing.tree;

import java.io.IOException;

import javax.swing.tree.*;

import com.globalmentor.swing.AbstractSwingApplication;

/**
 * A tree node that can dynamically load its children when needed. Child classes should override {@link #loadChildNodes()}.
 * 
 * This class also keeps track of whether there was an error loading nodes, resetting this error status when the nodes are unloaded.
 * 
 * @author Garret Wilson
 * @see #loadChildNodes()
 */
public abstract class DynamicTreeNode extends DefaultMutableTreeNode {

	/** Whether the child nodes have been loaded. */
	private boolean isChildNodesLoaded = false;

	/** @return Whether the child nodes have been loaded. */
	public boolean isChildNodesLoaded() {
		return isChildNodesLoaded;
	}

	/** The error encountered when trying to load, or null if no error was encountered. */
	private IOException loadError = null;

	/** @return The error encountered when trying to load, or null if no error was encountered. */
	public IOException getLoadError() {
		return loadError;
	}

	/**
	 * Sets the error encountered when trying to load
	 * @param error The error encountered when trying to load, or null if no error was encountered.
	 */
	protected void setLoadError(final IOException error) {
		loadError = error;
	}

	/**
	 * Creates a tree node that has no parent and no children, but which allows children.
	 */
	public DynamicTreeNode() {
		super(); //construct the parent class
	}

	/**
	 * Creates a tree node with no parent, no children, but which allows children, and initializes it with the specified user object.
	 * @param userObject An object provided by the user that constitutes the node's data
	 */
	public DynamicTreeNode(final Object userObject) {
		super(userObject); //construct the parent class
	}

	/**
	 * @return false so that we won't have to dynamically calculate whether we have children until we need to.
	 */
	public boolean isLeaf() {
		return false; //assume we're not a leaf
	}

	/**
	 * @return The number of children, loading the child nodes dynamically if needed.
	 * @see #ensureChildNodesLoaded
	 */
	public int getChildCount() {
		ensureChildNodesLoaded(); //make sure children have been loaded
		return super.getChildCount(); //return the number of children normally, now that we've loaded children if needed
	}

	/**
	 * Loads children if they haven't already been loaded. If there is an error loading the child nodes, the load error variable will be set.
	 * @see #loadChildNodes
	 */
	public void ensureChildNodesLoaded() {
		if(!isChildNodesLoaded()) { //if the children are not yet loaded
			isChildNodesLoaded = true; //show that we've loaded the child nodes (this is done before the actual loading so that future calls to getChildCount() won't cause reloading)
			removeAllChildren(); //make sure we've removed all children before trying to load the children
			try {
				loadChildNodes(); //load the child nodes
			} catch(final IOException ioException) { //if there was an error loading the child loads
				loadError = ioException; //save the load error
				AbstractSwingApplication.displayApplicationError(null, ioException); //display the error
			}
		}
	}

	/**
	 * Dynamically loads child nodes when needed. Must be overridden to appropriately load children.
	 * @throws IOException if there is an error loading the child nodes.
	 */
	protected abstract void loadChildNodes() throws IOException;

	/**
	 * Unloads all child nodes and sets the state to unloaded. Any error condition is reset.
	 */
	public void unloadChildNodes() {
		removeAllChildren(); //remove all the children
		isChildNodesLoaded = false; //show that we have no nodes loaded
		setLoadError(null); //show that there is no load error.
	}

}