23种设计模式在Android中的应用

/**
 * adapter 对象充当 AdapterView 和该View展现数据的桥梁。提供对数据的访问。
 * 还负责每一个 android.view.View 控件的数据集控制。
 * @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.
     * 当这个适配器使用的数据放生变化时候，注册一个观察者
     * @param observer the object that gets notified when the data set changes.
     * @param observer 当数据集发生变化，得到通知的对象
     */
    void registerDataSetObserver(DataSetObserver observer);

    /**
     * Unregister an observer that has previously been registered with this
     * adapter via {@link #registerDataSetObserver}.
     * 该方法是注销观察者作用，
     * @param observer the object to unregister.
     * @param observer 需要注销的观察者
     */
    void unregisterDataSetObserver(DataSetObserver observer);

    /**
     * How many items are in the data set represented by this Adapter.
     * adapter数据集大小
     * @return Count of items.
     * @return 返回数据集大小
     */
    int getCount();   
    
    /**
     * Get the data item associated with the specified position in the data set.
     * 返回数据集对应索引（position）的数据项对象
     * @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.
     * 返回数据集对应索引（position）的数据项Id
     * @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.
     * 如果相同的ID总是引用相同的对象，则为true。
     * @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.
     * 返回数据集中对应索引（position）指定的View。同样也可以创建一个视图或者通过xml布局inflate。
     * 如果是通过inflate获取视图时候，@param parent 可以是GridView 或者ListView等控件。
     * 除非你用{@link android.view.LayoutInflater#inflate(int, android.view.ViewGroup, boolean)}指定根视图并防止附着，否则使用默认的布局参数。
     * @param position The position of the item within the adapter's data set of the item whose view
     *        we want.
     * @param position 我们想要返回的视图,对应数据集索引（position）
     * @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 convertView 如果可以，重用旧视图。注意：需要检查视图不是null并且是适当的类型。如果不能重用，可以创建一个视图。
     * @param parent The parent that this view will eventually be attached to
     * @param parent 根视图
     * @return A View corresponding to the data at the specified position.
     * 返回呈现数据集索引对应数据项的视图。
     */
    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;
    }
}