PrintServicesLoader.java revision 66c96591e2ddb464c67e60dbf4193ef4ec8a620b 
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 java.util.List;
27
28/**
29 * Loader for the list of print services. Can be parametrized to select a subset.
30 *
31 * @hide
32 */
33public class PrintServicesLoader extends Loader<List<PrintServiceInfo>> {
34    /** What type of services to load. */
35    private final int mSelectionFlags;
36
37    /** The print manager to be used by this object */
38    private final @NonNull PrintManager mPrintManager;
39
40    /** Handler to sequentialize the delivery of the results to the main thread */
41    private Handler mHandler;
42
43    /** Listens for updates to the data from the platform */
44    private PrintManager.PrintServicesChangeListener mListener;
45
46    /**
47     * Create a new PrintServicesLoader.
48     *
49     * @param selectionFlags What type of services to load.
50     */
51    public PrintServicesLoader(@NonNull PrintManager printManager, @NonNull Context context,
52            int selectionFlags) {
53        super(context);
54        mPrintManager = printManager;
55        mSelectionFlags = selectionFlags;
56    }
57
58    @Override
59    protected void onForceLoad() {
60        queueNewResult();
61    }
62
63    /**
64     * Read the print services and queue it to be delivered on the main thread.
65     */
66    private void queueNewResult() {
67        Message m = mHandler.obtainMessage(0);
68        m.obj = mPrintManager.getPrintServices(mSelectionFlags);
69        mHandler.sendMessage(m);
70    }
71
72    @Override
73    protected void onStartLoading() {
74        mHandler = new MyHandler();
75        mListener = new PrintManager.PrintServicesChangeListener() {
76            @Override public void onPrintServicesChanged() {
77                queueNewResult();
78            }
79        };
80
81        mPrintManager.addPrintServicesChangeListener(mListener);
82
83        // Immediately deliver a result
84        deliverResult(mPrintManager.getPrintServices(mSelectionFlags));
85    }
86
87    @Override
88    protected void onStopLoading() {
89        if (mListener != null) {
90            mPrintManager.removePrintServicesChangeListener(mListener);
91            mListener = null;
92        }
93
94        if (mHandler != null) {
95            mHandler.removeMessages(0);
96            mHandler = null;
97        }
98    }
99
100    @Override
101    protected void onReset() {
102        onStopLoading();
103    }
104
105    /**
106     * Handler to sequentialize all the updates to the main thread.
107     */
108    private class MyHandler extends Handler {
109        /**
110         * Create a new handler on the main thread.
111         */
112        public MyHandler() {
113            super(getContext().getMainLooper());
114        }
115
116        @Override
117        public void handleMessage(Message msg) {
118            super.handleMessage(msg);
119
120            if (isStarted()) {
121                deliverResult((List<PrintServiceInfo>) msg.obj);
122            }
123        }
124    }
125}
126