001// Copyright 2008, 2010 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;
016
017/**
018 * A collection of parameters that may eventually be passed to an event handler method. Includes the
019 * ability to coerce
020 * or encode parameters as needed.
021 * 
022 * @see org.apache.tapestry5.commons.services.TypeCoercer
023 * @see org.apache.tapestry5.ValueEncoder
024 */
025public interface EventContext
026{
027    /**
028     * Returns the number of parameter values that can be extracted.
029     */
030    int getCount();
031
032    /**
033     * Extracts a parameter value and coerces or decodes it to the desired type.
034     * 
035     * @param desiredType
036     *            the type of value required
037     * @param index
038     *            identifies which parameter value to extract
039     * @return the value extracted and converted or coerced
040     * @throws RuntimeException
041     *             if the value can't be converted or the index is out of range
042     */
043    <T> T get(Class<T> desiredType, int index);
044
045    /**
046     * Extracts the value of each context value as a string.
047     * 
048     * @return context values
049     * @since 5.2.0
050     */
051    String[] toStrings();
052}