1/*
2 * Copyright (C) 2010 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.example.android.apis.app;
18
19import com.example.android.apis.R;
20
21import android.app.Activity;
22import android.app.Fragment;
23import android.app.FragmentManager;
24import android.os.Bundle;
25import android.view.LayoutInflater;
26import android.view.View;
27import android.view.ViewGroup;
28import android.view.View.OnClickListener;
29import android.widget.Button;
30import android.widget.ProgressBar;
31
32/**
33 * This example shows how you can use a Fragment to easily propagate state
34 * (such as threads) across activity instances when an activity needs to be
35 * restarted due to, for example, a configuration change.  This is a lot
36 * easier than using the raw Activity.onRetainNonConfiguratinInstance() API.
37 */
38public class FragmentRetainInstance extends Activity {
39    @Override
40    protected void onCreate(Bundle savedInstanceState) {
41        super.onCreate(savedInstanceState);
42
43        // First time init, create the UI.
44        if (savedInstanceState == null) {
45            getFragmentManager().beginTransaction().add(android.R.id.content,
46                    new UiFragment()).commit();
47        }
48    }
49
50    /**
51     * This is a fragment showing UI that will be updated from work done
52     * in the retained fragment.
53     */
54    public static class UiFragment extends Fragment {
55        RetainedFragment mWorkFragment;
56
57        @Override
58        public View onCreateView(LayoutInflater inflater, ViewGroup container,
59                Bundle savedInstanceState) {
60            View v = inflater.inflate(R.layout.fragment_retain_instance, container, false);
61
62            // Watch for button clicks.
63            Button button = (Button)v.findViewById(R.id.restart);
64            button.setOnClickListener(new OnClickListener() {
65                public void onClick(View v) {
66                    mWorkFragment.restart();
67                }
68            });
69
70            return v;
71        }
72
73        @Override
74        public void onActivityCreated(Bundle savedInstanceState) {
75            super.onActivityCreated(savedInstanceState);
76
77            FragmentManager fm = getFragmentManager();
78
79            // Check to see if we have retained the worker fragment.
80            mWorkFragment = (RetainedFragment)fm.findFragmentByTag("work");
81
82            // If not retained (or first time running), we need to create it.
83            if (mWorkFragment == null) {
84                mWorkFragment = new RetainedFragment();
85                // Tell it who it is working with.
86                mWorkFragment.setTargetFragment(this, 0);
87                fm.beginTransaction().add(mWorkFragment, "work").commit();
88            }
89        }
90
91    }
92
93    /**
94     * This is the Fragment implementation that will be retained across
95     * activity instances.  It represents some ongoing work, here a thread
96     * we have that sits around incrementing a progress indicator.
97     */
98    public static class RetainedFragment extends Fragment {
99        ProgressBar mProgressBar;
100        int mPosition;
101        boolean mReady = false;
102        boolean mQuiting = false;
103
104        /**
105         * This is the thread that will do our work.  It sits in a loop running
106         * the progress up until it has reached the top, then stops and waits.
107         */
108        final Thread mThread = new Thread() {
109            @Override
110            public void run() {
111                // We'll figure the real value out later.
112                int max = 10000;
113
114                // This thread runs almost forever.
115                while (true) {
116
117                    // Update our shared state with the UI.
118                    synchronized (this) {
119                        // Our thread is stopped if the UI is not ready
120                        // or it has completed its work.
121                        while (!mReady || mPosition >= max) {
122                            if (mQuiting) {
123                                return;
124                            }
125                            try {
126                                wait();
127                            } catch (InterruptedException e) {
128                            }
129                        }
130
131                        // Now update the progress.  Note it is important that
132                        // we touch the progress bar with the lock held, so it
133                        // doesn't disappear on us.
134                        mPosition++;
135                        max = mProgressBar.getMax();
136                        mProgressBar.setProgress(mPosition);
137                    }
138
139                    // Normally we would be doing some work, but put a kludge
140                    // here to pretend like we are.
141                    synchronized (this) {
142                        try {
143                            wait(50);
144                        } catch (InterruptedException e) {
145                        }
146                    }
147                }
148            }
149        };
150
151        /**
152         * Fragment initialization.  We way we want to be retained and
153         * start our thread.
154         */
155        @Override
156        public void onCreate(Bundle savedInstanceState) {
157            super.onCreate(savedInstanceState);
158
159            // Tell the framework to try to keep this fragment around
160            // during a configuration change.
161            setRetainInstance(true);
162
163            // Start up the worker thread.
164            mThread.start();
165        }
166
167        /**
168         * This is called when the Fragment's Activity is ready to go, after
169         * its content view has been installed; it is called both after
170         * the initial fragment creation and after the fragment is re-attached
171         * to a new activity.
172         */
173        @Override
174        public void onActivityCreated(Bundle savedInstanceState) {
175            super.onActivityCreated(savedInstanceState);
176
177            // Retrieve the progress bar from the target's view hierarchy.
178            mProgressBar = (ProgressBar)getTargetFragment().getView().findViewById(
179                    R.id.progress_horizontal);
180
181            // We are ready for our thread to go.
182            synchronized (mThread) {
183                mReady = true;
184                mThread.notify();
185            }
186        }
187
188        /**
189         * This is called when the fragment is going away.  It is NOT called
190         * when the fragment is being propagated between activity instances.
191         */
192        @Override
193        public void onDestroy() {
194            // Make the thread go away.
195            synchronized (mThread) {
196                mReady = false;
197                mQuiting = true;
198                mThread.notify();
199            }
200
201            super.onDestroy();
202        }
203
204        /**
205         * This is called right before the fragment is detached from its
206         * current activity instance.
207         */
208        @Override
209        public void onDetach() {
210            // This fragment is being detached from its activity.  We need
211            // to make sure its thread is not going to touch any activity
212            // state after returning from this function.
213            synchronized (mThread) {
214                mProgressBar = null;
215                mReady = false;
216                mThread.notify();
217            }
218
219            super.onDetach();
220        }
221
222        /**
223         * API for our UI to restart the progress thread.
224         */
225        public void restart() {
226            synchronized (mThread) {
227                mPosition = 0;
228                mThread.notify();
229            }
230        }
231    }
232}
233