core/java/android/widget/Adapter.java

/*
 * Copyright (C) 2006 The Android Open Source Project
 *
 * 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 android.widget;

import android.database.DataSetObserver;
import android.view.View;
import android.view.ViewGroup;

/**
 * An Adapter object acts as a bridge between an {@link AdapterView} and the
 * underlying data for that view. The Adapter provides access to the data items.
 * The Adapter is also responsible for making a {@link android.view.View} for
 * each item in the data set.
 * 
 * @see android.widget.ArrayAdapter
 * @see android.widget.CursorAdapter
 * @see android.widget.SimpleCursorAdapter
 */
public interface Adapter {
    /**
     * Register an observer that is called when changes happen to the data used by this adapter.
     *
     * @param observer the object that gets notified when the data set changes.
     */
    void registerDataSetObserver(DataSetObserver observer);

    /**
     * Unregister an observer that has previously been registered with this
     * adapter via {@link #registerDataSetObserver}.
     *
     * @param observer the object to unregister.
     */
    void unregisterDataSetObserver(DataSetObserver observer);

    /**
     * How many items are in the data set represented by this Adapter.
     * 
     * @return Count of items.
     */
    int getCount();   
    
    /**
     * Get the data item associated with the specified position in the data set.
     * 
     * @param position Position of the item whose data we want within the adapter's 
     * data set.
     * @return The data at the specified position.
     */
    Object getItem(int position);
    
    /**
     * Get the row id associated with the specified position in the list.
     * 
     * @param position The position of the item within the adapter's data set whose row id we want.
     * @return The id of the item at the specified position.
     */
    long getItemId(int position);
    
    /**
     * Indicates whether the item ids are stable across changes to the
     * underlying data.
     * 
     * @return True if the same id always refers to the same object.
     */
    boolean hasStableIds();
    
    /**
     * Get a View that displays the data at the specified position in the data set. You can either
     * create a View manually or inflate it from an XML layout file. When the View is inflated, the
     * parent View (GridView, ListView...) will apply default layout parameters unless you use
     * {@link android.view.LayoutInflater#inflate(int, android.view.ViewGroup, boolean)}
     * to specify a root view and to prevent attachment to the root.
     * 
     * @param position The position of the item within the adapter's data set of the item whose view
     *        we want.
     * @param convertView The old view to reuse, if possible. Note: You should check that this view
     *        is non-null and of an appropriate type before using. If it is not possible to convert
     *        this view to display the correct data, this method can create a new view.
     *        Heterogeneous lists can specify their number of view types, so that this View is
     *        always of the right type (see {@link #getViewTypeCount()} and
     *        {@link #getItemViewType(int)}).
     * @param parent The parent that this view will eventually be attached to
     * @return A View corresponding to the data at the specified position.
     */
    View getView(int position, View convertView, ViewGroup parent);

    /**
     * An item view type that causes the {@link AdapterView} to ignore the item
     * view. For example, this can be used if the client does not want a
     * particular view to be given for conversion in
     * {@link #getView(int, View, ViewGroup)}.
     * 
     * @see #getItemViewType(int)
     * @see #getViewTypeCount()
     */
    static final int IGNORE_ITEM_VIEW_TYPE = AdapterView.ITEM_VIEW_TYPE_IGNORE;
    
    /**
     * Get the type of View that will be created by {@link #getView} for the specified item.
     * 
     * @param position The position of the item within the adapter's data set whose view type we
     *        want.
     * @return An integer representing the type of View. Two views should share the same type if one
     *         can be converted to the other in {@link #getView}. Note: Integers must be in the
     *         range 0 to {@link #getViewTypeCount} - 1. {@link #IGNORE_ITEM_VIEW_TYPE} can
     *         also be returned.
     * @see #IGNORE_ITEM_VIEW_TYPE
     */
    int getItemViewType(int position);
    
    /**
     * <p>
     * Returns the number of types of Views that will be created by
     * {@link #getView}. Each type represents a set of views that can be
     * converted in {@link #getView}. If the adapter always returns the same
     * type of View for all items, this method should return 1.
     * </p>
     * <p>
     * This method will only be called when when the adapter is set on the
     * the {@link AdapterView}.
     * </p>
     * 
     * @return The number of types of Views that will be created by this adapter
     */
    int getViewTypeCount();
    
    static final int NO_SELECTION = Integer.MIN_VALUE;
 
     /**
      * @return true if this adapter doesn't contain any data.  This is used to determine
      * whether the empty view should be displayed.  A typical implementation will return
      * getCount() == 0 but since getCount() includes the headers and footers, specialized
      * adapters might want a different behavior.
      */
     boolean isEmpty();
}