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}