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    
015    package org.apache.tapestry5.grid;
016    
017    import 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     */
024    public 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    }