com.google.gwt.user.client.ui.SimplePanel.java Source code

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Here is the source code for com.google.gwt.user.client.ui.SimplePanel.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.user.client.ui;

import java.util.Iterator;
import java.util.NoSuchElementException;

import com.google.gwt.dom.client.Element;
import com.google.gwt.user.client.DOM;

/**
 * Base class for panels that contain only one widget.
 */
public class SimplePanel extends Panel implements HasOneWidget {
    Widget widget;

    /**
     * Creates an empty panel that uses a DIV for its contents.
     */
    public SimplePanel() {
        this(DOM.createDiv());
    }

    /**
     * Create a panel with the specified child widget.
     *
     * @param child
     *            the child to add to the panel
     */
    public SimplePanel(Widget child) {
        this();
        setWidget(child);
    }

    /**
     * Creates an empty panel that uses the specified browser element for its
     * contents.
     *
     * @param elem
     *            the browser element to use
     */
    protected SimplePanel(Element elem) {
        setElement(elem);
    }

    /**
     * Adds a widget to this panel.
     *
     * @param w
     *            the child widget to be added
     */
    @Override
    public void add(Widget w) {
        // Can't add() more than one widget to a SimplePanel.
        if (getWidget() != null) {
            throw new IllegalStateException("SimplePanel can only contain one child widget");
        }
        setWidget(w);
    }

    /**
     * Gets the panel's child widget.
     *
     * @return the child widget, or <code>null</code> if none is present
     */
    public Widget getWidget() {
        return widget;
    }

    public Iterator<Widget> iterator() {
        // Return a simple iterator that enumerates the 0 or 1 elements in this
        // panel.
        return new Iterator<Widget>() {
            boolean hasElement = widget != null;

            Widget returned = null;

            public boolean hasNext() {
                return hasElement;
            }

            public Widget next() {
                if (!hasElement || (widget == null)) {
                    throw new NoSuchElementException();
                }
                hasElement = false;
                return (returned = widget);
            }

            public void remove() {
                if (returned != null) {
                    SimplePanel.this.remove(returned);
                }
            }
        };
    }

    @Override
    public boolean remove(Widget w) {
        // Validate.
        if (widget != w) {
            return false;
        }
        // Orphan.
        try {
            orphan(w);
        } finally {
            // Physical detach.
            getContainerElement().removeChild(w.getElement());
            // Logical detach.
            widget = null;
        }
        return true;
    }

    public void setWidget(IsWidget w) {
        setWidget(asWidgetOrNull(w));
    }

    /**
     * Sets this panel's widget. Any existing child widget will be removed.
     *
     * @param w
     *            the panel's new widget, or <code>null</code> to clear the
     *            panel
     */
    public void setWidget(Widget w) {
        // Validate
        if (w == widget) {
            return;
        }
        // Detach new child.
        if (w != null) {
            w.removeFromParent();
        }
        // Remove old child.
        if (widget != null) {
            remove(widget);
        }
        // Logical attach.
        widget = w;
        if (w != null) {
            // Physical attach.
            DOM.appendChild(getContainerElement(), widget.getElement());
            adopt(w);
        }
    }

    /**
     * Override this method to specify that an element other than the root
     * element be the container for the panel's child widget. This can be useful
     * when you want to create a simple panel that decorates its contents.
     *
     * Note that this method continues to return the
     * {@link com.google.gwt.user.client.Element} class defined in the
     * <code>User</code> module to maintain backwards compatibility.
     *
     * @return the element to be used as the panel's container
     */
    protected Element getContainerElement() {
        return getElement();
    }
}