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Android example source code file (PersistentState.java)
This example Android source code file (PersistentState.java) is included in the DevDaily.com
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The PersistentState.java Android example source code
/*
* Copyright (C) 2007 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.example.android.apis.app;
// Need the following import to get access to the app resources, since this
// class is in a sub-package.
import com.example.android.apis.R;
import android.app.Activity;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.widget.EditText;
import android.widget.TextView;
/**
* Simple example of using persistent preferences to retain a screen's state.
* <p>This can be used as an alternative to the normal
* <code>onSaveInstanceState() mechanism, if you
* wish the state to persist even after an activity is finished.</p>
*
* <p>Note that using this approach requires more care, since you are sharing
* the persistent state potentially across multiple instances of the activity.
* In particular, if you allow a new instance of the activity to be launched
* directly on top of the existing instance, the state can get out of sync
* because the new instance is resumed before the old one is paused.</p>
*
* <p>For any persistent state that is not simplistic, a content
* provider is often a better choice.</p>
*
* <p>In this example we are currently saving and restoring the state of the
* top text editor, but not of the bottom text editor. You can see the difference
* by editing the two text fields, then going back from the activity and
* starting it again.</p>
*
* <h4>Demo
* App/Activity/Save & Restore State
*
* <h4>Source files
* <table class="LinkTable">
* <tr>
* <td class="LinkColumn">src/com.example.android.apis/app/PersistentState.java |
* <td class="DescrColumn">The Save/Restore Screen implementation
* </tr>
* <tr>
* <td class="LinkColumn">/res/any/layout/save_restore_state.xml
* <td class="DescrColumn">Defines contents of the screen
* </tr>
* </table>
*
*/
public class PersistentState extends Activity
{
/**
* Initialization of the Activity after it is first created. Here we use
* {@link android.app.Activity#setContentView setContentView()} to set up
* the Activity's content, and retrieve the EditText widget whose state we
* will persistent.
*/
@Override
protected void onCreate(Bundle savedInstanceState) {
// Be sure to call the super class.
super.onCreate(savedInstanceState);
// See assets/res/any/layout/save_restore_state.xml for this
// view layout definition, which is being set here as
// the content of our screen.
setContentView(R.layout.save_restore_state);
// Set message to be appropriate for this screen.
((TextView)findViewById(R.id.msg)).setText(R.string.persistent_msg);
// Retrieve the EditText widget whose state we will save.
mSaved = (EditText)findViewById(R.id.saved);
}
/**
* Upon being resumed we can retrieve the current state. This allows us
* to update the state if it was changed at any time while paused.
*/
@Override
protected void onResume() {
super.onResume();
SharedPreferences prefs = getPreferences(0);
String restoredText = prefs.getString("text", null);
if (restoredText != null) {
mSaved.setText(restoredText, TextView.BufferType.EDITABLE);
int selectionStart = prefs.getInt("selection-start", -1);
int selectionEnd = prefs.getInt("selection-end", -1);
if (selectionStart != -1 && selectionEnd != -1) {
mSaved.setSelection(selectionStart, selectionEnd);
}
}
}
/**
* Any time we are paused we need to save away the current state, so it
* will be restored correctly when we are resumed.
*/
@Override
protected void onPause() {
super.onPause();
SharedPreferences.Editor editor = getPreferences(0).edit();
editor.putString("text", mSaved.getText().toString());
editor.putInt("selection-start", mSaved.getSelectionStart());
editor.putInt("selection-end", mSaved.getSelectionEnd());
editor.commit();
}
private EditText mSaved;
}
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