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 android.support.v4.view;
18
19import android.content.Context;
20import android.os.Handler;
21import android.os.Handler.Callback;
22import android.os.Looper;
23import android.os.Message;
24import android.support.annotation.LayoutRes;
25import android.support.annotation.NonNull;
26import android.support.annotation.Nullable;
27import android.support.annotation.UiThread;
28import android.support.v4.util.Pools.SynchronizedPool;
29import android.util.AttributeSet;
30import android.util.Log;
31import android.view.LayoutInflater;
32import android.view.View;
33import android.view.ViewGroup;
34
35import java.util.concurrent.ArrayBlockingQueue;
36
37/**
38 * <p>Helper class for inflating layouts asynchronously. To use, construct
39 * an instance of {@link AsyncLayoutInflater} on the UI thread and call
40 * {@link #inflate(int, ViewGroup, OnInflateFinishedListener)}. The
41 * {@link OnInflateFinishedListener} will be invoked on the UI thread
42 * when the inflate request has completed.
43 *
44 * <p>This is intended for parts of the UI that are created lazily or in
45 * response to user interactions. This allows the UI thread to continue
46 * to be responsive & animate while the relatively heavy inflate
47 * is being performed.
48 *
49 * <p>For a layout to be inflated asynchronously it needs to have a parent
50 * whose {@link ViewGroup#generateLayoutParams(AttributeSet)} is thread-safe
51 * and all the Views being constructed as part of inflation must not create
52 * any {@link Handler}s or otherwise call {@link Looper#myLooper()}. If the
53 * layout that is trying to be inflated cannot be constructed
54 * asynchronously for whatever reason, {@link AsyncLayoutInflater} will
55 * automatically fall back to inflating on the UI thread.
56 *
57 * <p>NOTE that the inflated View hierarchy is NOT added to the parent. It is
58 * equivalent to calling {@link LayoutInflater#inflate(int, ViewGroup, boolean)}
59 * with attachToRoot set to false. Callers will likely want to call
60 * {@link ViewGroup#addView(View)} in the {@link OnInflateFinishedListener}
61 * callback at a minimum.
62 *
63 * <p>This inflater does not support setting a {@link LayoutInflater.Factory}
64 * nor {@link LayoutInflater.Factory2}. Similarly it does not support inflating
65 * layouts that contain fragments.
66 */
67public final class AsyncLayoutInflater {
68    private static final String TAG = "AsyncLayoutInflater";
69
70    private LayoutInflater mInflater;
71    private Handler mHandler;
72    private InflateThread mInflateThread;
73
74    public AsyncLayoutInflater(@NonNull Context context) {
75        mInflater = new BasicInflater(context);
76        mHandler = new Handler(mHandlerCallback);
77        mInflateThread = InflateThread.getInstance();
78    }
79
80    @UiThread
81    public void inflate(@LayoutRes int resid, @Nullable ViewGroup parent,
82            @NonNull OnInflateFinishedListener callback) {
83        if (callback == null) {
84            throw new NullPointerException("callback argument may not be null!");
85        }
86        InflateRequest request = mInflateThread.obtainRequest();
87        request.inflater = this;
88        request.resid = resid;
89        request.parent = parent;
90        request.callback = callback;
91        mInflateThread.enqueue(request);
92    }
93
94    private Callback mHandlerCallback = new Callback() {
95        @Override
96        public boolean handleMessage(Message msg) {
97            InflateRequest request = (InflateRequest) msg.obj;
98            if (request.view == null) {
99                request.view = mInflater.inflate(
100                        request.resid, request.parent, false);
101            }
102            request.callback.onInflateFinished(
103                    request.view, request.resid, request.parent);
104            mInflateThread.releaseRequest(request);
105            return true;
106        }
107    };
108
109    public interface OnInflateFinishedListener {
110        public void onInflateFinished(View view, int resid, ViewGroup parent);
111    }
112
113    private static class InflateRequest {
114        AsyncLayoutInflater inflater;
115        ViewGroup parent;
116        int resid;
117        View view;
118        OnInflateFinishedListener callback;
119    }
120
121    private static class BasicInflater extends LayoutInflater {
122        private static final String[] sClassPrefixList = {
123            "android.widget.",
124            "android.webkit.",
125            "android.app."
126        };
127
128        public BasicInflater(Context context) {
129            super(context);
130        }
131
132        @Override
133        public LayoutInflater cloneInContext(Context newContext) {
134            return new BasicInflater(newContext);
135        }
136
137        @Override
138        protected View onCreateView(String name, AttributeSet attrs) throws ClassNotFoundException {
139            for (String prefix : sClassPrefixList) {
140                try {
141                    View view = createView(name, prefix, attrs);
142                    if (view != null) {
143                        return view;
144                    }
145                } catch (ClassNotFoundException e) {
146                    // In this case we want to let the base class take a crack
147                    // at it.
148                }
149            }
150
151            return super.onCreateView(name, attrs);
152        }
153    }
154
155    private static class InflateThread extends Thread {
156        private static final InflateThread sInstance;
157        static {
158            sInstance = new InflateThread();
159            sInstance.start();
160        }
161
162        public static InflateThread getInstance() {
163            return sInstance;
164        }
165
166        private ArrayBlockingQueue<InflateRequest> mQueue
167                = new ArrayBlockingQueue<>(10);
168        private SynchronizedPool<InflateRequest> mRequestPool
169                = new SynchronizedPool<>(10);
170
171        @Override
172        public void run() {
173            while (true) {
174                InflateRequest request;
175                try {
176                    request = mQueue.take();
177                } catch (InterruptedException ex) {
178                    // Odd, just continue
179                    Log.w(TAG, ex);
180                    continue;
181                }
182
183                try {
184                    request.view = request.inflater.mInflater.inflate(
185                            request.resid, request.parent, false);
186                } catch (RuntimeException ex) {
187                    // Probably a Looper failure, retry on the UI thread
188                    Log.w(TAG, "Failed to inflate resource in the background! Retrying on the UI thread",
189                            ex);
190                }
191                Message.obtain(request.inflater.mHandler, 0, request)
192                        .sendToTarget();
193            }
194        }
195
196        public InflateRequest obtainRequest() {
197            InflateRequest obj = mRequestPool.acquire();
198            if (obj == null) {
199                obj = new InflateRequest();
200            }
201            return obj;
202        }
203
204        public void releaseRequest(InflateRequest obj) {
205            obj.callback = null;
206            obj.inflater = null;
207            obj.parent = null;
208            obj.resid = 0;
209            obj.view = null;
210            mRequestPool.release(obj);
211        }
212
213        public void enqueue(InflateRequest request) {
214            try {
215                mQueue.put(request);
216            } catch (InterruptedException e) {
217                throw new RuntimeException(
218                        "Failed to enqueue async inflate request", e);
219            }
220        }
221    }
222}
223