// Copyright 2007, 2008 The Apache Software Foundation

 //

 // 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 org.apache.tapestry5.grid;

 import java.util.List;

 /**

  * Defines how a {@link org.apache.tapestry5.corelib.components.Grid} component (and its sub-components) gain access to

  * the row data that is displayed on the page. In many cases, this is just a wrapper around a simple List, but the

  * abstractions exist to support access to a large data set that is accessible in sections.

  */

 public interface GridDataSource

 {

     /**

      * Returns the number of rows available in the data source.

      */

     int getAvailableRows();

     /**

      * Invoked to allow the source to prepare to present values. This gives the source a chance to pre-fetch data (when

      * appropriate) and informs the source of the desired sort order.  Sorting comes first, then extraction by range.

      *

      * @param startIndex      the starting index to be retrieved

      * @param endIndex        the ending index to be retrieved

      * @param sortConstraints identify how data is to be sorted

      */

     void prepare(int startIndex, int endIndex, List<SortConstraint> sortConstraints);

     /**

      * Returns the row value at the provided index. This method will be invoked in sequential order. In rare instances,

      * {@link #getAvailableRows()} may return a different number of rows than are actually available (i.e., the database

      * was changed between calls to {@link #getAvailableRows()} and the call to {@link #prepare(int, int,

      * java.util.List)}).  In that case, this method should return null for any out-of-range indexes.

      */

     Object getRowValue(int index);

     /**

      * Returns the type of value in the rows, or null if not known. This value is used to create a default {@link

      * org.apache.tapestry5.beaneditor.BeanModel} when no such model is explicitly provided.

      *

      * @return the row type, or null

      */

     Class getRowType();

 }