1/*
2 * Copyright (C) 2014 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
5 * in compliance with the License. You may obtain a copy of the License at
6 *
7 * http://www.apache.org/licenses/LICENSE-2.0
8 *
9 * Unless required by applicable law or agreed to in writing, software distributed under the License
10 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
11 * or implied. See the License for the specific language governing permissions and limitations under
12 * the License.
13 */
14package android.support.v17.leanback.widget;
15
16import android.view.View;
17import android.view.ViewGroup;
18
19/**
20 * A Presenter is used to generate {@link View}s and bind Objects to them on
21 * demand. It is closely related to concept of an {@link
22 * android.support.v7.widget.RecyclerView.Adapter RecyclerView.Adapter}, but is
23 * not position-based.
24 *
25 * <p>
26 * A trivial Presenter that takes a string and renders it into a {@link
27 * android.widget.TextView TextView}:
28 *
29 * <pre class="prettyprint">
30 * public class StringTextViewPresenter extends Presenter {
31 *     // This class does not need a custom ViewHolder, since it does not use
32 *     // a complex layout.
33 *
34 *     {@literal @}Override
35 *     public ViewHolder onCreateViewHolder(ViewGroup parent) {
36 *         return new ViewHolder(new TextView(parent.getContext()));
37 *     }
38 *
39 *     {@literal @}Override
40 *     public void onBindViewHolder(ViewHolder viewHolder, Object item) {
41 *         String str = (String) item;
42 *         TextView textView = (TextView) viewHolder.mView;
43 *
44 *         textView.setText(item);
45 *     }
46 *
47 *     {@literal @}Override
48 *     public void onUnbindViewHolder(ViewHolder viewHolder) {
49 *         // Nothing to unbind for TextView, but if this viewHolder had
50 *         // allocated bitmaps, they can be released here.
51 *     }
52 * }
53 * </pre>
54 */
55public abstract class Presenter {
56    /**
57     * ViewHolder can be subclassed and used to cache any view accessors needed
58     * to improve binding performance (for example, results of findViewById)
59     * without needing to subclass a View.
60     */
61    public static class ViewHolder {
62        public final View view;
63
64        public ViewHolder(View view) {
65            this.view = view;
66        }
67    }
68
69    /**
70     * Creates a new {@link View}.
71     */
72    public abstract ViewHolder onCreateViewHolder(ViewGroup parent);
73
74    /**
75     * Binds a {@link View} to an item.
76     */
77    public abstract void onBindViewHolder(ViewHolder viewHolder, Object item);
78
79    /**
80     * Unbinds a {@link View} from an item. Any expensive references may be
81     * released here, and any fields that are not bound for every item should be
82     * cleared here.
83     */
84    public abstract void onUnbindViewHolder(ViewHolder viewHolder);
85
86    /**
87     * Called when a view created by this presenter has been attached to a window.
88     *
89     * <p>This can be used as a reasonable signal that the view is about to be seen
90     * by the user. If the adapter previously freed any resources in
91     * {@link #onViewDetachedFromWindow(ViewHolder)}
92     * those resources should be restored here.</p>
93     *
94     * @param holder Holder of the view being attached
95     */
96    public void onViewAttachedToWindow(ViewHolder holder) {
97    }
98
99    /**
100     * Called when a view created by this presenter has been detached from its window.
101     *
102     * <p>Becoming detached from the window is not necessarily a permanent condition;
103     * the consumer of an presenter's views may choose to cache views offscreen while they
104     * are not visible, attaching and detaching them as appropriate.</p>
105     *
106     * Any view property animations should be cancelled here or the view may fail
107     * to be recycled.
108     *
109     * @param holder Holder of the view being detached
110     */
111    public void onViewDetachedFromWindow(ViewHolder holder) {
112        // If there are view property animations running then RecyclerView won't recycle.
113        cancelAnimationsRecursive(holder.view);
114    }
115
116    /**
117     * Utility method for removing all running animations on a view.
118     */
119    protected static void cancelAnimationsRecursive(View view) {
120        if (view != null && view.hasTransientState()) {
121            view.animate().cancel();
122            if (view instanceof ViewGroup) {
123                final int count = ((ViewGroup) view).getChildCount();
124                for (int i = 0; view.hasTransientState() && i < count; i++) {
125                    cancelAnimationsRecursive(((ViewGroup) view).getChildAt(i));
126                }
127            }
128        }
129    }
130
131    /**
132     * Called to set a click listener for the given view holder.
133     *
134     * The default implementation sets the click listener on the root view in the view holder.
135     * If the root view isn't focusable this method should be overridden to set the listener
136     * on the appropriate focusable child view(s).
137     *
138     * @param holder The view holder containing the view(s) on which the listener should be set.
139     * @param listener The click listener to be set.
140     */
141    public void setOnClickListener(ViewHolder holder, View.OnClickListener listener) {
142        holder.view.setOnClickListener(listener);
143    }
144}
145