com.vo.search.admin.client.ContentWidget.java Source code

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Here is the source code for com.vo.search.admin.client.ContentWidget.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.vo.search.admin.client;

import com.google.gwt.event.logical.shared.HasValueChangeHandlers;
import com.google.gwt.event.logical.shared.ValueChangeEvent;
import com.google.gwt.event.logical.shared.ValueChangeHandler;
import com.google.gwt.event.shared.HandlerRegistration;
import com.google.gwt.safehtml.shared.SafeHtml;
import com.google.gwt.safehtml.shared.SafeHtmlUtils;
import com.google.gwt.user.client.Window;
import com.google.gwt.user.client.rpc.AsyncCallback;
import com.google.gwt.user.client.ui.SimpleLayoutPanel;
import com.google.gwt.user.client.ui.Widget;

/**
 * <p>
 * A widget used to show GWT examples in the ContentPanel.
 * </p>
 * <p>
 * This {@link Widget} uses a lazy initialization mechanism so that the content
 * is not rendered until the onInitialize method is called, which happens the
 * first time the {@link Widget} is added to the page. The data in the source
 * and css tabs are loaded using an RPC call to the server.
 * </p>
 */
public abstract class ContentWidget extends SimpleLayoutPanel implements HasValueChangeHandlers<String> {

    /**
     * Generic callback used for asynchronously loaded data.
     * 
     * @param <T> the data type
     */
    public static interface Callback<T> {
        void onError();

        void onSuccess(T value);
    }

    /**
     * Get the simple filename of a class.
     * 
     * @param c the class
     */
    protected static String getSimpleName(Class<?> c) {
        String name = c.getName();
        return name.substring(name.lastIndexOf(".") + 1);
    }

    /**
     * A description of the example.
     */
    private final SafeHtml description;

    /**
     * True if this example has associated styles, false if not.
     */
    private final boolean hasStyle;

    /**
     * The name of the example.
     */
    private final String name;

    /**
     * The view that holds the name, description, and example.
     */
    private ContentWidgetView view;

    /**
     * Whether the demo widget has been initialized.
     */
    private boolean widgetInitialized;

    /**
     * Whether the demo widget is (asynchronously) initializing.
     */
    private boolean widgetInitializing;

    /**
     * Construct a {@link ContentWidget}.
     * 
     * @param name the text name of the example
     * @param description a text description of the example
     * @param hasStyle true if the example has associated styles
     */
    public ContentWidget(String name, String description, boolean hasStyle) {
        this(name, SafeHtmlUtils.fromString(description), hasStyle);
    }

    /**
     * Construct a {@link ContentWidget}.
     * 
     * @param name the text name of the example
     * @param description a safe html description of the example
     * @param hasStyle true if the example has associated styles
     */
    public ContentWidget(String name, SafeHtml description, boolean hasStyle) {
        this.name = name;
        this.description = description;
        this.hasStyle = hasStyle;
    }

    public HandlerRegistration addValueChangeHandler(ValueChangeHandler<String> handler) {
        return addHandler(handler, ValueChangeEvent.getType());
    }

    /**
     * Get the description of this example.
     * 
     * @return a description for this example
     */
    public final SafeHtml getDescription() {
        return description;
    }

    /**
     * Get the name of this example to use as a title.
     * 
     * @return a name for this example
     */
    public final String getName() {
        return name;
    }

    /**
     * Check if the widget should have margins.
     * 
     * @return true to use margins, false to flush against edges
     */
    public boolean hasMargins() {
        return true;
    }

    /**
     * Check if the widget should be wrapped in a scrollable div.
     * 
     * @return true to use add scrollbars, false not to
     */
    public boolean hasScrollableContent() {
        return true;
    }

    /**
     * Returns true if this widget has a style section.
     * 
     * @return true if style tab available
     */
    public final boolean hasStyle() {
        return hasStyle;
    }

    /**
     * When the widget is first initialized, this method is called. If it returns
     * a Widget, the widget will be added as the first tab. Return null to disable
     * the first tab.
     * 
     * @return the widget to add to the first tab
     */
    public abstract Widget onInitialize();

    /**
     * Called when initialization has completed and the widget has been added to
     * the page.
     */
    public void onInitializeComplete() {
    }

    protected abstract void asyncOnInitialize(final AsyncCallback<Widget> callback);

    @Override
    protected void onLoad() {
        if (view == null) {
            view = new ContentWidgetView(hasMargins(), hasScrollableContent());
            view.setName(getName());
            view.setDescription(getDescription());
            setWidget(view);
        }
        ensureWidgetInitialized();
        super.onLoad();
    }

    /**
     * Ensure that the demo widget has been initialized. Note that initialization
     * can fail if there is a network failure.
     */
    private void ensureWidgetInitialized() {
        if (widgetInitializing || widgetInitialized) {
            return;
        }

        widgetInitializing = true;

        asyncOnInitialize(new AsyncCallback<Widget>() {
            public void onFailure(Throwable reason) {
                widgetInitializing = false;
                Window.alert("Failed to download code for this widget (" + reason + ")");
            }

            public void onSuccess(Widget result) {
                widgetInitializing = false;
                widgetInitialized = true;

                Widget widget = result;
                if (widget != null) {
                    view.setExample(widget);
                }
                onInitializeComplete();
            }
        });
    }

}