    001// Copyright 2007, 2008 The Apache Software Foundation
    002//
    003// Licensed under the Apache License, Version 2.0 (the "License");
    004// you may not use this file except in compliance with the License.
    005// You may obtain a copy of the License at
    006//
    007//     http://www.apache.org/licenses/LICENSE-2.0
    008//
    009// Unless required by applicable law or agreed to in writing, software
    010// distributed under the License is distributed on an "AS IS" BASIS,
    011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    012// See the License for the specific language governing permissions and
    013// limitations under the License.
    014
    015package org.apache.tapestry5.grid;
    016
    017import java.util.List;
    018
    019/**
    020 * Defines how a {@link org.apache.tapestry5.corelib.components.Grid} component (and its sub-components) gain access to
    021 * the row data that is displayed on the page. In many cases, this is just a wrapper around a simple List, but the
    022 * abstractions exist to support access to a large data set that is accessible in sections.
    023 */
    024public interface GridDataSource
    025{
    026    /**
    027     * Returns the number of rows available in the data source.
    028     */
    029    int getAvailableRows();
    030
    031    /**
    032     * Invoked to allow the source to prepare to present values. This gives the source a chance to pre-fetch data (when
    033     * appropriate) and informs the source of the desired sort order.  Sorting comes first, then extraction by range.
    034     *
    035     * @param startIndex      the starting index to be retrieved
    036     * @param endIndex        the ending index to be retrieved
    037     * @param sortConstraints identify how data is to be sorted
    038     */
    039    void prepare(int startIndex, int endIndex, List<SortConstraint> sortConstraints);
    040
    041    /**
    042     * Returns the row value at the provided index. This method will be invoked in sequential order. In rare instances,
    043     * {@link #getAvailableRows()} may return a different number of rows than are actually available (i.e., the database
    044     * was changed between calls to {@link #getAvailableRows()} and the call to {@link #prepare(int, int,
    045     * java.util.List)}).  In that case, this method should return null for any out-of-range indexes.
    046     */
    047    Object getRowValue(int index);
    048
    049    /**
    050     * Returns the type of value in the rows, or null if not known. This value is used to create a default {@link
    051     * org.apache.tapestry5.beaneditor.BeanModel} when no such model is explicitly provided.
    052     *
    053     * @return the row type, or null
    054     */
    055    Class getRowType();
    056}