Java tutorial
/* * 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.annotation.Nullable; 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 the adapter is set on 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(); /** * Gets a string representation of the adapter data that can help * {@link android.service.autofill.AutofillService} autofill the view backed by the adapter. * * <p> * It should only be set (i.e., non-{@code null} if the values do not represent PII * (Personally Identifiable Information - sensitive data such as email addresses, * credit card numbers, passwords, etc...). For * example, it's ok to return a list of month names, but not a list of usernames. A good rule of * thumb is that if the adapter data comes from static resources, such data is not PII - see * {@link android.view.ViewStructure#setDataIsSensitive(boolean)} for more info. * * @return {@code null} by default, unless implementations override it. */ default @Nullable CharSequence[] getAutofillOptions() { return null; } }