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 
17 package com.android.documentsui.base;
18 
19 import android.os.AsyncTask;
20 
21 /**
22  * An {@link AsyncTask} that guards work with checks that a paired {@link Check}
23  * has not yet given signals to stop progress.
24  *
25  * <p>Use this type of task for greater safety when executing tasks that might complete
26  * after the owner of the task has explicitly given a signal to stop progress.
27  *
28  * <p>Also useful as tasks can be static, limiting scope, but still have access to
29  * signal from the owning class.
30  *
31  * @template Input input type
32  * @template Output output type
33  */
34 public abstract class CheckedTask<Input, Output>
35         extends AsyncTask<Input, Void, Output> {
36 
37     private Check mCheck;
38 
CheckedTask(Check check)39     public CheckedTask(Check check) {
40         mCheck = check;
41     }
42 
43     /** Called prior to run being executed. Analogous to {@link AsyncTask#onPreExecute} */
prepare()44     protected void prepare() {}
45 
46     /** Analogous to {@link AsyncTask#doInBackground} */
run(Input... input)47     protected abstract Output run(Input... input);
48 
49     /** Analogous to {@link AsyncTask#onPostExecute} */
finish(Output output)50     protected abstract void finish(Output output);
51 
52     @Override
onPreExecute()53     protected final void onPreExecute() {
54         if (mCheck.stop()) {
55             return;
56         }
57         prepare();
58     }
59 
60     @Override
doInBackground(Input... input)61     protected final Output doInBackground(Input... input) {
62         if (mCheck.stop()) {
63             return null;
64         }
65         return run(input);
66     }
67 
68     @Override
onPostExecute(Output result)69     protected final void onPostExecute(Output result) {
70         if (mCheck.stop()) {
71             return;
72         }
73         finish(result);
74     }
75 
76     @FunctionalInterface
77     public interface Check {
stop()78         boolean stop();
79     }
80 }
81