RequestKey.java revision c5644927c0e7e121049b063046296ee8a59a4b37 
1/*
2 * Copyright (C) 2013 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.bitmap;
18
19import android.os.ParcelFileDescriptor;
20
21import java.io.IOException;
22import java.io.InputStream;
23
24/**
25 * The decode task uses this class to get input to decode. You must implement at least one of
26 * {@link #createFileDescriptorFactoryAsync(RequestKey, Callback)} or {@link #createInputStream()}.
27 * {@link DecodeTask} will prioritize
28 * {@link #createFileDescriptorFactoryAsync(RequestKey, Callback)} before falling back to
29 * {@link #createInputStream()}.
30 *
31 * <p>
32 * Clients of this interface must also implement {@link #equals(Object)} and {@link #hashCode()} as
33 * this object will be used as a cache key.
34 *
35 * <p>
36 * The following is a high level view of the interactions between RequestKey and the rest of the
37 * system.
38 *
39 *       BasicBitmapDrawable
40 *           UI Thread
41 *              ++
42 *       bind() ||            Background Thread
43 *              |+-------------------->+
44 *              || createFDFasync()   ||
45 *              ||                    || Download from url
46 *              ||                    || Cache on disk
47 *              ||                    ||
48 *              ||                    vv
49 *              |<--------------------+x
50 *              ||        FDFcreated()
51 *              ||
52 *              ||
53 *              ||                DecodeTask
54 *              ||             AsyncTask Thread
55 *              |+-------------------->+
56 *              || new().execute()    ||
57 *              ||                    || Decode from FDF
58 *              ||                    || or createInputStream()
59 *              ||                    ||
60 *              ||                    vv
61 *              |<--------------------+x
62 *              ||  onDecodeComplete()
63 *              vv
64 * invalidate() xx
65 */
66public interface RequestKey {
67
68    /**
69     * Create an {@link FileDescriptorFactory} for a local file stored on the device and pass it to
70     * the given callback. This method will be called first; if it returns null,
71     * {@link #createInputStream()} will be called.
72     *
73     * Clients should implement this method if files are in the local cache folder, or if files must
74     * be downloaded and cached.
75     *
76     * This method must be called from the UI thread.
77     *
78     * @param key      The key to create a FileDescriptorFactory for. This key will be passed to the
79     *                 callback so it can check whether the key has changed.
80     * @param callback The callback to notify once the FileDescriptorFactory has been created. Do
81     *                 not invoke the callback directly from this method. Instead, create a handler
82     *                 and post a Runnable.
83     *
84     * @return If the client will attempt to create a FileDescriptorFactory, return a Cancelable
85     * object to cancel the asynchronous task. If the client wants to create an InputStream instead,
86     * return null. The callback must be notified if and only if the client returns a Cancelable
87     * object and not null.
88     */
89    public Cancelable createFileDescriptorFactoryAsync(RequestKey key, Callback callback);
90
91    /**
92     * Create an {@link InputStream} for the source. This method will be called if
93     * {@link #createFileDescriptorFactoryAsync(RequestKey, Callback)} returns null.
94     *
95     * Clients should implement this method if files exist in the assets/ folder, or for prototypes
96     * that open a connection directly on a URL (be warned that this will cause GCs).
97     *
98     * This method can be called from any thread.
99     */
100    public InputStream createInputStream() throws IOException;
101
102    /**
103     * Return true if the image source may have be oriented in either portrait or landscape, and
104     * will need to be automatically re-oriented based on accompanying Exif metadata.
105     *
106     * This method can be called from any thread.
107     */
108    public boolean hasOrientationExif() throws IOException;
109
110    /**
111     * Callback for creating the {@link FileDescriptorFactory} asynchronously.
112     */
113    public interface Callback {
114
115        /**
116         * Notifies that the {@link FileDescriptorFactory} has been created. This must be called on
117         * the UI thread.
118         * @param key The key that the FileDescriptorFactory was created for. The callback should
119         *            check that the key has not changed.
120         * @param factory The FileDescriptorFactory to decode from. Pass null to cancel decode.
121         */
122        void fileDescriptorFactoryCreated(RequestKey key, FileDescriptorFactory factory);
123    }
124
125    public interface FileDescriptorFactory {
126        ParcelFileDescriptor createFileDescriptor();
127    }
128
129    /**
130     * Interface for a background task that is cancelable.
131     */
132    public interface Cancelable {
133
134        /**
135         * Cancel the background task. This must be called on the UI thread.
136         */
137        void cancel();
138    }
139}