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[Android Dev] 2.2 Preference
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<span class="label label-default">Series</span>
Part 6 of «Associate Android Developer Fast Track»
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目录
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<div id="toc"><ul><li><a class="toc-href" href="#data-persistance" title="Data Persistance">Data Persistance</a></li><li><a class="toc-href" href="#preferencefragments" title="PreferenceFragments">PreferenceFragments</a><ul><li><a class="toc-href" href="#fragment" title="Fragment">Fragment</a></li><li><a class="toc-href" href="#preferencefragment" title="PreferenceFragment">PreferenceFragment</a></li></ul></li><li><a class="toc-href" href="#adding-a-settings-screen-from-a-pref-xml-file-recipe_1" title="Adding a settings screen from a pref-xml file Recipe">Adding a settings screen from a pref-xml file Recipe</a><ul><li><a class="toc-href" href="#1-create-a-settings-activity" title="1. create a settings activity">1. create a settings activity</a></li><li><a class="toc-href" href="#2-create-a-preferences-xml" title="2. create a preferences xml">2. create a preferences xml</a></li><li><a class="toc-href" href="#3-create-a-class-that-extends-preferencefragment" title="3. create a class that extends PreferenceFragment">3. create a class that extends PreferenceFragment</a></li><li><a class="toc-href" href="#4-change-root-element-of-settings-activity-to-a-fragment" title="4. change root element of settings activity to a fragment">4. change root element of settings activity to a fragment</a></li><li><a class="toc-href" href="#5-add-a-preferencetheme" title="5. add a preferenceTheme">5. add a preferenceTheme</a></li><li><a class="toc-href" href="#6-read-from-sharedpreferences-and-update" title="6. read from SharedPreferences and update">6. read from SharedPreferences and update</a></li><li><a class="toc-href" href="#best-practice-using-resources-instead-of-using-constant-iterals-everywhere" title="best practice: using resources instead of using constant iterals everywhere.">best practice: using resources instead of using constant iterals everywhere.</a></li></ul></li><li><a class="toc-href" href="#preferencechangelistener_1" title="PreferenceChangeListener">PreferenceChangeListener</a><ul><li><a class="toc-href" href="#reciept" title="Reciept">Reciept</a></li></ul></li><li><a class="toc-href" href="#list-preference_1" title="List Preference">List Preference</a><ul><li><a class="toc-href" href="#listpreference-recipe" title="ListPreference Recipe">ListPreference Recipe</a></li><li><a class="toc-href" href="#add-summary-for-list-preference" title="add summary for list preference">add summary for list preference</a></li></ul></li></ul></div>
</div>
</div>
<p>Save settings and configurations. </p>
<h2 id="data-persistance">Data Persistance</h2>
<p>5 different ways of data persistance: </p>
<ul>
<li><code>onSavedInstanceState()</code>: store state of views in k-v pairs (Bundles), used when screen rotates / app killed by system, <strong>temperary.</strong></li>
<li><code>SharedPreferences</code>: save k-v pairs to a file, can save <strong>primitive types</strong>.</li>
<li>SQLite database: complicated data types</li>
<li>Internal / External Storage: save large files to local phone, ex. podcast app / camera app.</li>
<li>Server: ex. leaderboard for a game (Firebase)</li>
</ul>
<p><img alt="" class="img-responsive" src="../images/andev_p2e2_pref/pasted_image.png"/></p>
<h2 id="preferencefragments">PreferenceFragments</h2>
<p>PreferenceFragment is a class to handle the storing of user preferences. </p>
<h3 id="fragment">Fragment</h3>
<p><code>Fragment</code> is a class that represents a modular and reusable piece of an <code>Activity</code>.
ex. a booklist-bookdetail app, for tablets want both screens (list/detail) on the same screen ⇒ put the 2 screens into <code>Fragment</code>s, and re-use them. </p>
<h3 id="preferencefragment">PreferenceFragment</h3>
<p>populated with preferences defined in an XML,
and (automatically) update k-v pairs in a sharedpref file. </p>
<p><img alt="" class="img-responsive" src="../images/andev_p2e2_pref/pasted_image002.png"/></p>
<p>in the pref XML file: define what are in the preferences, keys(names) and default values, and summary of a pref item. </p>
<h2 id="adding-a-settings-screen-from-a-pref-xml-file-recipe_1">Adding a settings screen from a pref-xml file Recipe</h2>
<h3 id="1-create-a-settings-activity">1. create a settings activity</h3>
<ul>
<li>add a menu xml, in the xml, add a menu item</li>
<li>show menu in mian activity</li>
<li>when "settings" item is clicked: open settings activity</li>
</ul>
<h3 id="2-create-a-preferences-xml">2. create a preferences xml</h3>
<ul>
<li>setup gradle dependency (build.gradle):</li>
</ul>
<p><code>compile 'com.android.support:preference-v7:25.1.0</code>'</p>
<ul>
<li>
<p>create a xml file in <code>res/xml</code> folder, add CheckBoxPreference. </p>
<p><?xml version="1.0" encoding="utf-8"?>
<preferencescreen xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto">
<checkboxpreference android:defaultvalue="true" android:key="show_base" android:summaryoff="not shown" android:summaryon="shown" app:title="@string/show_base"></checkboxpreference>
</preferencescreen></p>
</li>
</ul>
<h3 id="3-create-a-class-that-extends-preferencefragment">3. create a class that extends PreferenceFragment</h3>
<div class="highlight"><pre><span class="code-line"><span></span><span class="err">// TODO (2) Create a class called SettingsFragment that extends PreferenceFragmentCompat</span></span>
<span class="code-line"><span class="err">public class SettingsFragment extends PreferenceFragmentCompat{</span></span>
<span class="code-line"><span class="err">// TODO (5) In SettingsFragment's onCreatePreferences method add the preference file using the</span></span>
<span class="code-line"><span class="err">// addPreferencesFromResource method</span></span>
<span class="code-line"><span class="err"> @Override</span></span>
<span class="code-line"><span class="err"> public void onCreatePreferences(Bundle savedInstanceState, String rootKey) {</span></span>
<span class="code-line"><span class="err"> addPreferencesFromResource(R.xml.pref_visualizer);</span></span>
<span class="code-line"><span class="err"> }</span></span>
<span class="code-line"><span class="err">}</span></span>
</pre></div>
<h3 id="4-change-root-element-of-settings-activity-to-a-fragment">4. change root element of settings activity to a fragment</h3>
<div class="highlight"><pre><span class="code-line"><span></span><span class="cp"><?xml version="1.0" encoding="utf-8"?></span></span>
<span class="code-line"><span class="nt"><fragment</span> <span class="na">xmlns:android=</span><span class="s">"http://schemas.android.com/apk/res/android"</span></span>
<span class="code-line"> <span class="na">xmlns:tools=</span><span class="s">"http://schemas.android.com/tools"</span></span>
<span class="code-line"> <span class="na">android:id=</span><span class="s">"@+id/activity_settings"</span></span>
<span class="code-line"> <span class="na">android:name=</span><span class="s">"android.example.com.visualizerpreferences.SettingsFragment"</span></span>
<span class="code-line"> <span class="na">android:layout_width=</span><span class="s">"match_parent"</span></span>
<span class="code-line"> <span class="na">android:layout_height=</span><span class="s">"match_parent"</span><span class="nt">></span></span>
<span class="code-line"><span class="nt"></fragment></span></span>
</pre></div>
<h3 id="5-add-a-preferencetheme">5. add a preferenceTheme</h3>
<p>in <code>res/values/styles.xml</code>:</p>
<p><code><item name="preferenceTheme">@style/PreferenceThemeOverlay</item></code></p>
<h3 id="6-read-from-sharedpreferences-and-update">6. read from SharedPreferences and update</h3>
<p>in <code>onStart</code> or <code>onResume</code> of main activity: </p>
<div class="highlight"><pre><span class="code-line"><span></span><span class="o">//</span> <span class="n">TODO</span> <span class="p">(</span><span class="mi">2</span><span class="p">)</span> <span class="k">Get</span> <span class="n">a</span> <span class="n">reference</span> <span class="k">to</span> <span class="n">the</span> <span class="k">default</span> <span class="n">shared</span> <span class="n">preferences</span> <span class="k">from</span> <span class="n">the</span> <span class="n">PreferenceManager</span> <span class="k">class</span></span>
<span class="code-line"><span class="n">SharedPreferences</span> <span class="n">pref</span> <span class="o">=</span> <span class="n">PreferenceManager</span><span class="p">.</span><span class="n">getDefaultSharedPreferences</span><span class="p">(</span><span class="n">this</span><span class="p">);</span></span>
<span class="code-line"><span class="o">//</span> <span class="n">TODO</span> <span class="p">(</span><span class="mi">3</span><span class="p">)</span> <span class="k">Get</span> <span class="n">the</span> <span class="n">value</span> <span class="k">of</span> <span class="n">the</span> <span class="n">show_bass</span> <span class="n">checkbox</span> <span class="n">preference</span> <span class="k">and</span> <span class="n">use</span> <span class="n">it</span> <span class="k">to</span> <span class="k">call</span> <span class="n">setShowBass</span></span>
<span class="code-line"></span>
<span class="code-line"><span class="n">mVisualizerView</span><span class="p">.</span><span class="n">setShowBass</span><span class="p">(</span><span class="n">pref</span><span class="p">.</span><span class="n">getBoolean</span><span class="p">(</span><span class="ss">"show_bass"</span><span class="p">,</span> <span class="k">true</span><span class="p">));</span></span>
</pre></div>
<h3 id="best-practice-using-resources-instead-of-using-constant-iterals-everywhere">best practice: using resources instead of using constant iterals everywhere.</h3>
<p>i.e. extract strings/bools into strings.xml or bools.xml: </p>
<div class="highlight"><pre><span class="code-line"><span></span><span class="nt"><string</span> <span class="na">name=</span><span class="s">"pref_show_bass_title"</span><span class="nt">></span>Show Bass<span class="nt"></string></span></span>
<span class="code-line"><span class="nt"><string</span> <span class="na">name=</span><span class="s">"pref_show_bass_key"</span> <span class="na">translatable=</span><span class="s">"false"</span><span class="nt">></span>show_bass<span class="nt"></string></span></span>
<span class="code-line"><span class="nt"><string</span> <span class="na">name=</span><span class="s">"pref_show_bass_summaryon"</span><span class="nt">></span>Shown<span class="nt"></string></span></span>
<span class="code-line"><span class="nt"><string</span> <span class="na">name=</span><span class="s">"pref_show_bass_summaryoff"</span><span class="nt">></span>Hidden<span class="nt"></string></span></span>
<span class="code-line"><span class="nt"><bool</span> <span class="na">name=</span><span class="s">"pref_show_bass_default"</span><span class="nt">></span>true<span class="nt"></bool></span></span>
</pre></div>
<p>in other xml files: </p>
<div class="highlight"><pre><span class="code-line"><span></span><span class="err"><CheckBoxPreference</span></span>
<span class="code-line"><span class="err"> android:defaultValue="@bool/pref_show_bass_default"</span></span>
<span class="code-line"><span class="err"> android:key="@string/pref_show_bass_key"</span></span>
<span class="code-line"><span class="err"> android:summaryOff="@string/pref_show_bass_summaryoff"</span></span>
<span class="code-line"><span class="err"> android:summaryOn="@string/pref_show_bass_summaryon"</span></span>
<span class="code-line"><span class="err"> android:title="@string/perf_show_bass_title" /></span></span>
</pre></div>
<p>in java files: </p>
<div class="highlight"><pre><span class="code-line"><span></span><span class="err">mVisualizerView.setShowBass(perf.getBoolean(getString(R.string.pref_show_bass_key),</span></span>
<span class="code-line"><span class="err"> getResources().getBoolean(R.bool.pref_show_bass_default)));</span></span>
</pre></div>
<h2 id="preferencechangelistener_1">PreferenceChangeListener</h2>
<p>instead of updating preferences in onStart/onResume of main activity, use <code>onPreferenceChangeListener</code>, this is called whenever a sharedpref is changed.<br/>
<img alt="" class="img-responsive" src="../images/andev_p2e2_pref/pasted_image004.png"/></p>
<h3 id="reciept">Reciept</h3>
<p><strong>step 1</strong>: determine the activity who's UI needs to be changed when pref changes
— in our case, is the main activity</p>
<p><strong>step 2</strong>: let this activity implement <code>OnSharedPreferenceChangeListener</code> and override the <code>onSharedPreferenceChanged</code> method</p>
<div class="highlight"><pre><span class="code-line"><span></span><span class="err">@Override</span></span>
<span class="code-line"><span class="err">public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {</span></span>
<span class="code-line"><span class="err"> Preference pref = findPreference(key);</span></span>
<span class="code-line"><span class="err"> if (!(pref instanceof CheckBoxPreference)) {</span></span>
<span class="code-line"><span class="err"> String value = sharedPreferences.getString(key, "");</span></span>
<span class="code-line"><span class="err"> setPreferenceSummary(pref, value);</span></span>
<span class="code-line"><span class="err"> }</span></span>
<span class="code-line"><span class="err">}</span></span>
</pre></div>
<p><strong>step 3</strong>: link this Listener to the SharedPreference object that it listens to, using <code>registerOnSharedPreferenceChangeListener</code>
in onCreate(): </p>
<div class="highlight"><pre><span class="code-line"><span></span><span class="err">SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);</span></span>
<span class="code-line"><span class="err">sharedPreferences.registerOnSharedPreferenceChangeListener(this);</span></span>
</pre></div>
<p><strong>step 4</strong>: unregister the Listener when activity is shut down
in onDestroy(): </p>
<div class="highlight"><pre><span class="code-line"><span></span><span class="err">@Override</span></span>
<span class="code-line"><span class="err">protected void onDestroy() {</span></span>
<span class="code-line"><span class="err"> super.onDestroy();</span></span>
<span class="code-line"><span class="err"> PreferenceManager.getDefaultSharedPreferences(this)</span></span>
<span class="code-line"><span class="err"> .unregisterOnSharedPreferenceChangeListener(this);</span></span>
<span class="code-line"><span class="err">}</span></span>
</pre></div>
<h2 id="list-preference_1">List Preference</h2>
<p>Compared to <code>CheckBoxPreference</code>, <code>ListPreference</code> offers an array of possible choices. </p>
<h3 id="listpreference-recipe">ListPreference Recipe</h3>
<p>define options labels/values in <code>res/values/strings.xml</code>:</p>
<div class="highlight"><pre><span class="code-line"><span></span><span class="nt"><string</span> <span class="na">name=</span><span class="s">"pref_color_key"</span><span class="nt">></span>pref_color<span class="nt"></string></span></span>
<span class="code-line"><span class="nt"><string</span> <span class="na">name=</span><span class="s">"pref_color_title"</span><span class="nt">></span>Pick a color<span class="nt"></string></span></span>
<span class="code-line"><span class="nt"><string</span> <span class="na">name=</span><span class="s">"pref_color_red_label"</span><span class="nt">></span>Red<span class="nt"></string></span></span>
<span class="code-line"><span class="nt"><string</span> <span class="na">name=</span><span class="s">"pref_color_blue_label"</span><span class="nt">></span>Blue<span class="nt"></string></span></span>
<span class="code-line"><span class="nt"><string</span> <span class="na">name=</span><span class="s">"pref_color_green_label"</span><span class="nt">></span>Green<span class="nt"></string></span></span>
<span class="code-line"></span>
<span class="code-line"><span class="nt"><string</span> <span class="na">name=</span><span class="s">"pref_color_red_value"</span> <span class="na">translatable=</span><span class="s">"false"</span><span class="nt">></span>color_red<span class="nt"></string></span></span>
<span class="code-line"><span class="nt"><string</span> <span class="na">name=</span><span class="s">"pref_color_blue_value"</span> <span class="na">translatable=</span><span class="s">"false"</span><span class="nt">></span>color_blue<span class="nt"></string></span></span>
<span class="code-line"><span class="nt"><string</span> <span class="na">name=</span><span class="s">"pref_color_green_value"</span> <span class="na">translatable=</span><span class="s">"false"</span><span class="nt">></span>color_green<span class="nt"></string></span></span>
</pre></div>
<p>(note: <code>xx_value</code> is for internal usage, <code>xx_lablel</code> is what is shown on screen to users)</p>
<p>create <code>res/values/arrays.xml</code>: </p>
<div class="highlight"><pre><span class="code-line"><span></span><span class="cp"><?xml version="1.0" encoding="utf-8"?></span></span>
<span class="code-line"><span class="c"><!-- TODO (3) Add a res->values->arrays.xml file which contains two arrays, one for</span></span>
<span class="code-line"><span class="c"> labels and one for values. The arrays should contain strings found in this file--></span></span>
<span class="code-line"><span class="nt"><resources></span></span>
<span class="code-line"> <span class="nt"><array</span> <span class="na">name=</span><span class="s">"pref_color_option_labels"</span><span class="nt">></span></span>
<span class="code-line"> <span class="nt"><item></span>@string/pref_color_red_label<span class="nt"></item></span></span>
<span class="code-line"> <span class="nt"><item></span>@string/pref_color_blue_label<span class="nt"></item></span></span>
<span class="code-line"> <span class="nt"><item></span>@string/pref_color_green_label<span class="nt"></item></span></span>
<span class="code-line"> <span class="nt"></array></span></span>
<span class="code-line"> <span class="nt"><array</span> <span class="na">name=</span><span class="s">"pref_color_option_values"</span><span class="nt">></span></span>
<span class="code-line"> <span class="nt"><item></span>@string/pref_color_red_value<span class="nt"></item></span></span>
<span class="code-line"> <span class="nt"><item></span>@string/pref_color_blue_value<span class="nt"></item></span></span>
<span class="code-line"> <span class="nt"><item></span>@string/pref_color_green_value<span class="nt"></item></span></span>
<span class="code-line"> <span class="nt"></array></span></span>
<span class="code-line"><span class="nt"></resources></span></span>
</pre></div>
<p>in preference xml: add a ListPreference element</p>
<div class="highlight"><pre><span class="code-line"><span></span><span class="err"><ListPreference</span></span>
<span class="code-line"><span class="err"> android:defaultValue="@string/pref_color_red_value"</span></span>
<span class="code-line"><span class="err"> android:entries="@array/pref_color_option_labels"</span></span>
<span class="code-line"><span class="err"> android:entryValues="@array/pref_color_option_values"</span></span>
<span class="code-line"><span class="err"> android:key="@string/pref_color_key"</span></span>
<span class="code-line"><span class="err"> android:title="@string/pref_color_title"/></span></span>
</pre></div>
<p>finally in main activity: </p>
<div class="highlight"><pre><span class="code-line"><span></span><span class="err">String default_color_value = getString(R.string.pref_color_red_value);</span></span>
<span class="code-line"><span class="err">mVisualizerView.setColor(sharedPreferences.getString(getString(R.string.pref_color_key),</span></span>
<span class="code-line"><span class="err"> default_color_value) );</span></span>
</pre></div>
<h3 id="add-summary-for-list-preference">add summary for list preference</h3>
<p>we have to this programatically in the java code. </p>
<p>Here is the recipe: </p>
<p><strong>step 1</strong>: let the SettingsFragment class implement OnSharedPreferenceChangeListener:</p>
<div class="highlight"><pre><span class="code-line"><span></span><span class="err">// TODO (1) Implement OnSharedPreferenceChangeListener</span></span>
<span class="code-line"><span class="err">public class SettingsFragment extends PreferenceFragmentCompat implements OnSharedPreferenceChangeListener</span></span>
</pre></div>
<p><strong>step 2</strong>:set preference's summary by <code>setSummary()</code>:</p>
<div class="highlight"><pre><span class="code-line"><span></span><span class="o">//</span><span class="w"> </span><span class="n">TODO</span><span class="w"> </span><span class="p">(</span><span class="mi">2</span><span class="p">)</span><span class="w"> </span><span class="k">Create</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">setPreferenceSummary</span><span class="w"> </span><span class="n">which</span><span class="w"> </span><span class="n">takes</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">Preference</span><span class="w"> </span><span class="ow">and</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="k">value</span><span class="w"> </span><span class="k">as</span><span class="w"> </span><span class="k">parameters</span><span class="p">.</span><span class="w"></span></span>
<span class="code-line"><span class="o">//</span><span class="w"> </span><span class="n">This</span><span class="w"> </span><span class="k">method</span><span class="w"> </span><span class="n">should</span><span class="w"> </span><span class="k">check</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">preference</span><span class="w"> </span><span class="k">is</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">ListPreference</span><span class="w"> </span><span class="ow">and</span><span class="p">,</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">so</span><span class="p">,</span><span class="w"> </span><span class="n">find</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">label</span><span class="w"></span></span>
<span class="code-line"><span class="o">//</span><span class="w"> </span><span class="n">associated</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="k">value</span><span class="p">.</span><span class="w"> </span><span class="n">You</span><span class="w"> </span><span class="n">can</span><span class="w"> </span><span class="n">do</span><span class="w"> </span><span class="n">this</span><span class="w"> </span><span class="k">by</span><span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">findIndexOfValue</span><span class="w"> </span><span class="ow">and</span><span class="w"> </span><span class="n">getEntries</span><span class="w"> </span><span class="n">methods</span><span class="w"></span></span>
<span class="code-line"><span class="o">//</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">Preference</span><span class="p">.</span><span class="w"></span></span>
<span class="code-line"><span class="n">private</span><span class="w"> </span><span class="n">void</span><span class="w"> </span><span class="n">setPreferenceSummary</span><span class="p">(</span><span class="n">Preference</span><span class="w"> </span><span class="n">sharedPref</span><span class="p">,</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="k">value</span><span class="p">)</span><span class="w"> </span><span class="err">{</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">sharedPref</span><span class="w"> </span><span class="n">instanceof</span><span class="w"> </span><span class="n">ListPreference</span><span class="p">)</span><span class="w"> </span><span class="err">{</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">ListPreference</span><span class="w"> </span><span class="n">listPref</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="n">ListPreference</span><span class="p">)</span><span class="w"> </span><span class="n">sharedPref</span><span class="p">;</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="nc">int</span><span class="w"> </span><span class="n">idx</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">listPref</span><span class="p">.</span><span class="n">findIndexOfValue</span><span class="p">(</span><span class="k">value</span><span class="p">);</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">listPref</span><span class="p">.</span><span class="n">setSummary</span><span class="p">(</span><span class="n">listPref</span><span class="p">.</span><span class="n">getEntries</span><span class="p">()</span><span class="o">[</span><span class="n">idx</span><span class="o">]</span><span class="p">);</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="err">}</span><span class="w"></span></span>
<span class="code-line"><span class="err">}</span><span class="w"></span></span>
</pre></div>
<p><strong>step 3</strong>: set pref summary in onCreatePreferences: </p>
<div class="highlight"><pre><span class="code-line"><span></span><span class="nv">@Override</span><span class="w"></span></span>
<span class="code-line"><span class="k">public</span><span class="w"> </span><span class="n">void</span><span class="w"> </span><span class="n">onCreatePreferences</span><span class="p">(</span><span class="n">Bundle</span><span class="w"> </span><span class="n">bundle</span><span class="p">,</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="n">s</span><span class="p">)</span><span class="w"> </span><span class="err">{</span><span class="w"></span></span>
<span class="code-line"></span>
<span class="code-line"><span class="w"> </span><span class="o">//</span><span class="w"> </span><span class="k">Add</span><span class="w"> </span><span class="n">visualizer</span><span class="w"> </span><span class="n">preferences</span><span class="p">,</span><span class="w"> </span><span class="n">defined</span><span class="w"> </span><span class="ow">in</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="nc">XML</span><span class="w"> </span><span class="k">file</span><span class="w"> </span><span class="ow">in</span><span class="w"> </span><span class="n">res</span><span class="o">-></span><span class="nc">xml</span><span class="o">-></span><span class="n">pref_visualizer</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">addPreferencesFromResource</span><span class="p">(</span><span class="n">R</span><span class="p">.</span><span class="nc">xml</span><span class="p">.</span><span class="n">pref_visualizer</span><span class="p">);</span><span class="w"></span></span>
<span class="code-line"></span>
<span class="code-line"><span class="w"> </span><span class="o">//</span><span class="w"> </span><span class="n">TODO</span><span class="w"> </span><span class="p">(</span><span class="mi">3</span><span class="p">)</span><span class="w"> </span><span class="k">Get</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">preference</span><span class="w"> </span><span class="n">screen</span><span class="p">,</span><span class="w"> </span><span class="k">get</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">number</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">preferences</span><span class="w"> </span><span class="ow">and</span><span class="w"> </span><span class="k">iterate</span><span class="w"> </span><span class="n">through</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="o">//</span><span class="w"> </span><span class="ow">all</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">preferences</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">it</span><span class="w"> </span><span class="k">is</span><span class="w"> </span><span class="ow">not</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">checkbox</span><span class="w"> </span><span class="n">preference</span><span class="p">,</span><span class="w"> </span><span class="k">call</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">setSummary</span><span class="w"> </span><span class="k">method</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="o">//</span><span class="w"> </span><span class="n">passing</span><span class="w"> </span><span class="ow">in</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">preference</span><span class="w"> </span><span class="ow">and</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="k">value</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">preference</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">PreferenceScreen</span><span class="w"> </span><span class="n">prefScreen</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">getPreferenceScreen</span><span class="p">();</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="nc">int</span><span class="w"> </span><span class="n">nPrefs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">prefScreen</span><span class="p">.</span><span class="n">getPreferenceCount</span><span class="p">();</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="k">for</span><span class="p">(</span><span class="nc">int</span><span class="w"> </span><span class="n">i</span><span class="o">=</span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o"><</span><span class="n">nPrefs</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="err">{</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">Preference</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">prefScreen</span><span class="p">.</span><span class="n">getPreference</span><span class="p">(</span><span class="n">i</span><span class="p">);</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="k">if</span><span class="p">(</span><span class="n">p</span><span class="w"> </span><span class="n">instanceof</span><span class="w"> </span><span class="n">CheckBoxPreference</span><span class="p">)</span><span class="w"> </span><span class="k">continue</span><span class="p">;</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="err">{</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="k">value</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">prefScreen</span><span class="p">.</span><span class="n">getSharedPreferences</span><span class="p">().</span><span class="n">getString</span><span class="p">(</span><span class="n">p</span><span class="p">.</span><span class="n">getKey</span><span class="p">(),</span><span class="w"> </span><span class="ss">""</span><span class="p">);</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">setPreferenceSummary</span><span class="p">(</span><span class="n">p</span><span class="p">,</span><span class="w"> </span><span class="k">value</span><span class="p">);</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="err">}</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="err">}</span><span class="w"></span></span>
<span class="code-line"><span class="err">}</span><span class="w"></span></span>
</pre></div>
<p><strong>step 4</strong>: implement onSharedPreferenceChanged listener: </p>
<div class="highlight"><pre><span class="code-line"><span></span><span class="o">//</span><span class="w"> </span><span class="n">TODO</span><span class="w"> </span><span class="p">(</span><span class="mi">4</span><span class="p">)</span><span class="w"> </span><span class="n">Override</span><span class="w"> </span><span class="n">onSharedPreferenceChanged</span><span class="w"> </span><span class="ow">and</span><span class="p">,</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">it</span><span class="w"> </span><span class="k">is</span><span class="w"> </span><span class="ow">not</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">checkbox</span><span class="w"> </span><span class="n">preference</span><span class="p">,</span><span class="w"></span></span>
<span class="code-line"><span class="o">//</span><span class="w"> </span><span class="k">call</span><span class="w"> </span><span class="n">setPreferenceSummary</span><span class="w"> </span><span class="k">on</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">changed</span><span class="w"> </span><span class="n">preference</span><span class="w"></span></span>
<span class="code-line"><span class="nv">@Override</span><span class="w"></span></span>
<span class="code-line"><span class="k">public</span><span class="w"> </span><span class="n">void</span><span class="w"> </span><span class="n">onSharedPreferenceChanged</span><span class="p">(</span><span class="n">SharedPreferences</span><span class="w"> </span><span class="n">sharedPreferences</span><span class="p">,</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="k">key</span><span class="p">)</span><span class="w"> </span><span class="err">{</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">sharedPreferences</span><span class="w"> </span><span class="n">instanceof</span><span class="w"> </span><span class="n">CheckBoxPreference</span><span class="p">)</span><span class="w"> </span><span class="k">return</span><span class="p">;</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="k">else</span><span class="err">{</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">Preference</span><span class="w"> </span><span class="n">pref</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">findPreference</span><span class="p">(</span><span class="k">key</span><span class="p">);</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="k">value</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">sharedPreferences</span><span class="p">.</span><span class="n">getString</span><span class="p">(</span><span class="k">key</span><span class="p">,</span><span class="w"> </span><span class="ss">""</span><span class="p">);</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">setPreferenceSummary</span><span class="p">(</span><span class="n">pref</span><span class="p">,</span><span class="w"> </span><span class="k">value</span><span class="p">);</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="err">}</span><span class="w"></span></span>
<span class="code-line"></span>
<span class="code-line"><span class="err">}</span><span class="w"></span></span>
</pre></div>
<p><strong>step 5</strong>: finally register/unregister the listener in oncreate/ondestroy: </p>
<div class="highlight"><pre><span class="code-line"><span></span><span class="o">//</span><span class="w"> </span><span class="n">TODO</span><span class="w"> </span><span class="p">(</span><span class="mi">5</span><span class="p">)</span><span class="w"> </span><span class="n">Register</span><span class="w"> </span><span class="ow">and</span><span class="w"> </span><span class="n">unregister</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">OnSharedPreferenceChange</span><span class="w"> </span><span class="n">listener</span><span class="w"> </span><span class="p">(</span><span class="n">this</span><span class="w"> </span><span class="k">class</span><span class="p">)</span><span class="w"> </span><span class="ow">in</span><span class="w"></span></span>
<span class="code-line"><span class="o">//</span><span class="w"> </span><span class="n">onCreate</span><span class="w"> </span><span class="ow">and</span><span class="w"> </span><span class="n">onDestroy</span><span class="w"> </span><span class="n">respectively</span><span class="p">.</span><span class="w"></span></span>
<span class="code-line"><span class="nv">@Override</span><span class="w"></span></span>
<span class="code-line"><span class="k">public</span><span class="w"> </span><span class="n">void</span><span class="w"> </span><span class="n">onCreate</span><span class="p">(</span><span class="n">Bundle</span><span class="w"> </span><span class="n">savedInstanceState</span><span class="p">)</span><span class="w"> </span><span class="err">{</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">super</span><span class="p">.</span><span class="n">onCreate</span><span class="p">(</span><span class="n">savedInstanceState</span><span class="p">);</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">getPreferenceScreen</span><span class="p">().</span><span class="n">getSharedPreferences</span><span class="p">()</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="p">.</span><span class="n">registerOnSharedPreferenceChangeListener</span><span class="p">(</span><span class="n">this</span><span class="p">);</span><span class="w"></span></span>
<span class="code-line"><span class="err">}</span><span class="w"></span></span>
<span class="code-line"></span>
<span class="code-line"><span class="nv">@Override</span><span class="w"></span></span>
<span class="code-line"><span class="k">public</span><span class="w"> </span><span class="n">void</span><span class="w"> </span><span class="n">onDestroy</span><span class="p">()</span><span class="w"> </span><span class="err">{</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">super</span><span class="p">.</span><span class="n">onDestroy</span><span class="p">();</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">getPreferenceScreen</span><span class="p">().</span><span class="n">getSharedPreferences</span><span class="p">()</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="p">.</span><span class="n">unregisterOnSharedPreferenceChangeListener</span><span class="p">(</span><span class="n">this</span><span class="p">);</span><span class="w"></span></span>
<span class="code-line"><span class="err">}</span><span class="w"></span></span>
</pre></div>
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<div id="toc"><ul><li><a class="toc-href" href="#data-persistance" title="Data Persistance">Data Persistance</a></li><li><a class="toc-href" href="#preferencefragments" title="PreferenceFragments">PreferenceFragments</a><ul><li><a class="toc-href" href="#fragment" title="Fragment">Fragment</a></li><li><a class="toc-href" href="#preferencefragment" title="PreferenceFragment">PreferenceFragment</a></li></ul></li><li><a class="toc-href" href="#adding-a-settings-screen-from-a-pref-xml-file-recipe_1" title="Adding a settings screen from a pref-xml file Recipe">Adding a settings screen from a pref-xml file Recipe</a><ul><li><a class="toc-href" href="#1-create-a-settings-activity" title="1. create a settings activity">1. create a settings activity</a></li><li><a class="toc-href" href="#2-create-a-preferences-xml" title="2. create a preferences xml">2. create a preferences xml</a></li><li><a class="toc-href" href="#3-create-a-class-that-extends-preferencefragment" title="3. create a class that extends PreferenceFragment">3. create a class that extends PreferenceFragment</a></li><li><a class="toc-href" href="#4-change-root-element-of-settings-activity-to-a-fragment" title="4. change root element of settings activity to a fragment">4. change root element of settings activity to a fragment</a></li><li><a class="toc-href" href="#5-add-a-preferencetheme" title="5. add a preferenceTheme">5. add a preferenceTheme</a></li><li><a class="toc-href" href="#6-read-from-sharedpreferences-and-update" title="6. read from SharedPreferences and update">6. read from SharedPreferences and update</a></li><li><a class="toc-href" href="#best-practice-using-resources-instead-of-using-constant-iterals-everywhere" title="best practice: using resources instead of using constant iterals everywhere.">best practice: using resources instead of using constant iterals everywhere.</a></li></ul></li><li><a class="toc-href" href="#preferencechangelistener_1" title="PreferenceChangeListener">PreferenceChangeListener</a><ul><li><a class="toc-href" href="#reciept" title="Reciept">Reciept</a></li></ul></li><li><a class="toc-href" href="#list-preference_1" title="List Preference">List Preference</a><ul><li><a class="toc-href" href="#listpreference-recipe" title="ListPreference Recipe">ListPreference Recipe</a></li><li><a class="toc-href" href="#add-summary-for-list-preference" title="add summary for list preference">add summary for list preference</a></li></ul></li></ul></div>
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