/*
 * Copyright 2000-2013 JetBrains s.r.o.
 *
 * 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 com.intellij.openapi.actionSystem;

import org.jetbrains.annotations.NonNls;
import org.jetbrains.annotations.Nullable;

/**
 * Allows a component hosting actions to provide context information to the actions. When a specific
 * data item is requested, the component hierarchy is walked up from the currently focused component,
 * and every component implementing the <code>DataProvider</code> interface is queried for the data
 * until one of them returns the data. Data items can also be mapped to each other - for example,
 * if a data provider provides an item for {@link CommonDataKeys#NAVIGATABLE}, an item for
 * {@link CommonDataKeys#NAVIGATABLE_ARRAY} can be generated from it automatically.
 *
 * @see DataContext
 */
public interface DataProvider {
  /**
   * Returns the object corresponding to the specified data identifier. Some of the supported
   * data identifiers are defined in the {@link com.intellij.openapi.actionSystem.PlatformDataKeys} class.
   *
   * @param dataId the data identifier for which the value is requested.
   * @return the value, or null if no value is available in the current context for this identifier.
   */
  @Nullable
  Object getData(@NonNls String dataId);
}