1 /*
2  * Copyright (C) 2007 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.example.android.apis.app;
18 
19 // Need the following import to get access to the app resources, since this
20 // class is in a sub-package.
21 
22 import com.example.android.apis.R;
23 
24 import android.app.Activity;
25 import android.content.SharedPreferences;
26 import android.os.Bundle;
27 import android.widget.EditText;
28 import android.widget.TextView;
29 
30 /**
31  * Simple example of using persistent preferences to retain a screen's state.
32  * <p>This can be used as an alternative to the normal
33  * <code>onSaveInstanceState()</code> mechanism, if you
34  * wish the state to persist even after an activity is finished.</p>
35  *
36  * <p>Note that using this approach requires more care, since you are sharing
37  * the persistent state potentially across multiple instances of the activity.
38  * In particular, if you allow a new instance of the activity to be launched
39  * directly on top of the existing instance, the state can get out of sync
40  * because the new instance is resumed before the old one is paused.</p>
41  *
42  * <p>For any persistent state that is not simplistic, a content
43  * provider is often a better choice.</p>
44  *
45  * <p>In this example we are currently saving and restoring the state of the
46  * top text editor, but not of the bottom text editor.  You can see the difference
47  * by editing the two text fields, then going back from the activity and
48  * starting it again.</p>
49  *
50  * <h4>Demo</h4>
51  * App/Activity/Save &amp; Restore State
52  *
53  * <h4>Source files</h4>
54  * <table class="LinkTable">
55  *         <tr>
56  *             <td class="LinkColumn">src/com.example.android.apis/app/PersistentState.java</td>
57  *             <td class="DescrColumn">The Save/Restore Screen implementation</td>
58  *         </tr>
59  *         <tr>
60  *             <td class="LinkColumn">/res/any/layout/save_restore_state.xml</td>
61  *             <td class="DescrColumn">Defines contents of the screen</td>
62  *         </tr>
63  * </table>
64  *
65  */
66 public class PersistentState extends Activity
67 {
68     /**
69      * Initialization of the Activity after it is first created.  Here we use
70      * {@link android.app.Activity#setContentView setContentView()} to set up
71      * the Activity's content, and retrieve the EditText widget whose state we
72      * will persistent.
73      */
74     @Override
onCreate(Bundle savedInstanceState)75     protected void onCreate(Bundle savedInstanceState) {
76         // Be sure to call the super class.
77         super.onCreate(savedInstanceState);
78 
79         // See assets/res/any/layout/save_restore_state.xml for this
80         // view layout definition, which is being set here as
81         // the content of our screen.
82         setContentView(R.layout.save_restore_state);
83 
84         // Set message to be appropriate for this screen.
85         ((TextView)findViewById(R.id.msg)).setText(R.string.persistent_msg);
86 
87         // Retrieve the EditText widget whose state we will save.
88         mSaved = (EditText)findViewById(R.id.saved);
89     }
90 
91     /**
92      * Upon being resumed we can retrieve the current state.  This allows us
93      * to update the state if it was changed at any time while paused.
94      */
95     @Override
onResume()96     protected void onResume() {
97         super.onResume();
98 
99         SharedPreferences prefs = getPreferences(0);
100         String restoredText = prefs.getString("text", null);
101         if (restoredText != null) {
102             mSaved.setText(restoredText, TextView.BufferType.EDITABLE);
103 
104             int selectionStart = prefs.getInt("selection-start", -1);
105             int selectionEnd = prefs.getInt("selection-end", -1);
106             if (selectionStart != -1 && selectionEnd != -1) {
107                 mSaved.setSelection(selectionStart, selectionEnd);
108             }
109         }
110     }
111 
112     /**
113      * Any time we are paused we need to save away the current state, so it
114      * will be restored correctly when we are resumed.
115      */
116     @Override
onPause()117     protected void onPause() {
118         super.onPause();
119 
120         SharedPreferences.Editor editor = getPreferences(0).edit();
121         editor.putString("text", mSaved.getText().toString());
122         editor.putInt("selection-start", mSaved.getSelectionStart());
123         editor.putInt("selection-end", mSaved.getSelectionEnd());
124         editor.commit();
125     }
126 
127     private EditText mSaved;
128 }
129