PrintServicesLoader.java revision 7e01895e6972c0ebc552215b1207a519529af3fd 
1/*
2 * Copyright (C) 2016 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.print;
18
19import android.annotation.NonNull;
20import android.content.Context;
21import android.content.Loader;
22import android.os.Handler;
23import android.os.Message;
24import android.printservice.PrintServiceInfo;
25
26import com.android.internal.util.Preconditions;
27
28import java.util.List;
29
30/**
31 * Loader for the list of print services. Can be parametrized to select a subset.
32 *
33 * @hide
34 */
35public class PrintServicesLoader extends Loader<List<PrintServiceInfo>> {
36    /** What type of services to load. */
37    private final int mSelectionFlags;
38
39    /** The print manager to be used by this object */
40    private final @NonNull PrintManager mPrintManager;
41
42    /** Handler to sequentialize the delivery of the results to the main thread */
43    private final @NonNull Handler mHandler;
44
45    /** Listens for updates to the data from the platform */
46    private PrintManager.PrintServicesChangeListener mListener;
47
48    /**
49     * Create a new PrintServicesLoader.
50     *
51     * @param printManager   The print manager supplying the data
52     * @param context        Context of the using object
53     * @param selectionFlags What type of services to load.
54     */
55    public PrintServicesLoader(@NonNull PrintManager printManager, @NonNull Context context,
56            int selectionFlags) {
57        super(Preconditions.checkNotNull(context));
58        mHandler = new MyHandler();
59        mPrintManager = Preconditions.checkNotNull(printManager);
60        mSelectionFlags = Preconditions.checkFlagsArgument(selectionFlags,
61                PrintManager.ALL_SERVICES);
62    }
63
64    @Override
65    protected void onForceLoad() {
66        queueNewResult();
67    }
68
69    /**
70     * Read the print services and queue it to be delivered on the main thread.
71     */
72    private void queueNewResult() {
73        Message m = mHandler.obtainMessage(0);
74        m.obj = mPrintManager.getPrintServices(mSelectionFlags);
75        mHandler.sendMessage(m);
76    }
77
78    @Override
79    protected void onStartLoading() {
80        mListener = new PrintManager.PrintServicesChangeListener() {
81            @Override public void onPrintServicesChanged() {
82                queueNewResult();
83            }
84        };
85
86        mPrintManager.addPrintServicesChangeListener(mListener, null);
87
88        // Immediately deliver a result
89        deliverResult(mPrintManager.getPrintServices(mSelectionFlags));
90    }
91
92    @Override
93    protected void onStopLoading() {
94        if (mListener != null) {
95            mPrintManager.removePrintServicesChangeListener(mListener);
96            mListener = null;
97        }
98
99        mHandler.removeMessages(0);
100    }
101
102    @Override
103    protected void onReset() {
104        onStopLoading();
105    }
106
107    /**
108     * Handler to sequentialize all the updates to the main thread.
109     */
110    private class MyHandler extends Handler {
111        /**
112         * Create a new handler on the main thread.
113         */
114        public MyHandler() {
115            super(getContext().getMainLooper());
116        }
117
118        @Override
119        public void handleMessage(Message msg) {
120            if (isStarted()) {
121                deliverResult((List<PrintServiceInfo>) msg.obj);
122            }
123        }
124    }
125}
126