ChannelsPosterPrefetcher.java revision 633eb826b8c97731dfc5ef12c7bf78a63734275d 
1/*
2 * Copyright (C) 2015 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.android.tv.menu;
18
19import android.content.Context;
20import android.os.Handler;
21import android.os.Looper;
22import android.os.Message;
23import android.support.annotation.MainThread;
24import android.support.annotation.NonNull;
25import android.util.Log;
26
27import com.android.tv.R;
28import com.android.tv.common.SoftPreconditions;
29import com.android.tv.common.WeakHandler;
30import com.android.tv.data.Channel;
31import com.android.tv.data.Program;
32import com.android.tv.data.ProgramDataManager;
33
34import java.util.List;
35
36/**
37 * A poster image prefetcher to show the program poster art in the Channels row faster.
38 */
39public class ChannelsPosterPrefetcher {
40    private static final String TAG = "PosterPrefetcher";
41    private static final boolean DEBUG = false;
42    private static final int MSG_PREFETCH_IMAGE = 1000;
43    private static final int ONDEMAND_POSTER_PREFETCH_DELAY_MILLIS = 500;  // 500 milliseconds
44
45    private final ProgramDataManager mProgramDataManager;
46    private final ChannelsRowAdapter mChannelsAdapter;
47    private final int mPosterArtWidth;
48    private final int mPosterArtHeight;
49    private final Context mContext;
50    private final Handler mHandler = new PrefetchHandler(this);
51
52    private boolean isCanceled;
53
54    /**
55     * Create {@link ChannelsPosterPrefetcher} object with given parameters.
56     */
57    public ChannelsPosterPrefetcher(Context context, ProgramDataManager programDataManager,
58            ChannelsRowAdapter adapter) {
59        mProgramDataManager = programDataManager;
60        mChannelsAdapter = adapter;
61        mPosterArtWidth = context.getResources().getDimensionPixelSize(
62                R.dimen.card_image_layout_width);
63        mPosterArtHeight = context.getResources().getDimensionPixelSize(
64                R.dimen.card_image_layout_height);
65        mContext = context.getApplicationContext();
66    }
67
68    /**
69     * Start prefetching of program poster art of recommendation.
70     */
71    public void prefetch() {
72        SoftPreconditions.checkState(!isCanceled, TAG, "Prefetch called after cancel was called.");
73        if (isCanceled) {
74            return;
75        }
76        if (DEBUG) Log.d(TAG, "startPrefetching()");
77        /*
78         * When a user browse channels, this method could be called many times. We don't need to
79         * prefetch the intermediate channels. So ignore previous schedule.
80         */
81        mHandler.removeMessages(MSG_PREFETCH_IMAGE);
82        mHandler.sendMessageDelayed(mHandler.obtainMessage(MSG_PREFETCH_IMAGE),
83                ONDEMAND_POSTER_PREFETCH_DELAY_MILLIS);
84    }
85
86    /**
87     * Cancels pending and current prefetch requests.
88     */
89    public void cancel() {
90        isCanceled = true;
91        mHandler.removeCallbacksAndMessages(null);
92    }
93
94    @MainThread // ProgramDataManager.getCurrentProgram must be called from the main thread
95    private void doPrefetchImages() {
96        if (DEBUG) Log.d(TAG, "doPrefetchImages() started");
97
98        // This executes on the main thread, but since the item list is expected to be about 5 items
99        // and ImageLoader spawns an async task so this is fast enough. 1 ms in local testing.
100        List<ChannelsRowItem> items = mChannelsAdapter.getItemList();
101        if (items != null) {
102            for (ChannelsRowItem item : items) {
103                if (isCanceled) {
104                    return;
105                }
106                Channel channel = item.getChannel();
107                if (!Channel.isValid(channel)) {
108                    continue;
109                }
110                channel.prefetchImage(mContext, Channel.LOAD_IMAGE_TYPE_CHANNEL_LOGO,
111                        mPosterArtWidth, mPosterArtHeight);
112                Program program = mProgramDataManager.getCurrentProgram(channel.getId());
113                if (program != null) {
114                    program.prefetchPosterArt(mContext, mPosterArtWidth, mPosterArtHeight);
115                }
116            }
117        }
118        if (DEBUG) {
119            Log.d(TAG, "doPrefetchImages() finished. ImageLoader may still have async tasks for "
120                            + "channels " + items);
121        }
122    }
123
124    private static class PrefetchHandler extends WeakHandler<ChannelsPosterPrefetcher> {
125        public PrefetchHandler(ChannelsPosterPrefetcher ref) {
126            // doPrefetchImages must be called from the main thread.
127            super(Looper.getMainLooper(), ref);
128        }
129
130        @Override
131        @MainThread
132        public void handleMessage(Message msg, @NonNull ChannelsPosterPrefetcher prefetcher) {
133            switch (msg.what) {
134                case MSG_PREFETCH_IMAGE:
135                    prefetcher.doPrefetchImages();
136                    break;
137            }
138        }
139    }
140}
141