Home > Articles > Programming > Java

This chapter is from the book

Saving User Preferences

Because an activity’s state is not saved automatically during its lifecycle, you need to save user preferences so that you can redisplay an activity in the correct state. Let’s see how to do that.

Creating a New Activity

Applications often consist of more than one activity. Let’s create a new Settings activity to enable and disable vibration and create the best possible experience for the user.

  1. Create a new activity called activity_settings via the Android New Activity wizard. Select BlankActivity as the template, Settings as the activity name, and activity_settings as the layout file. Type Settings as the title.
  2. Open the activity_settings file. Change the RelativeLayout to a LinearLayout with a vertical orientation:

    <LinearLayout xmlns:android=http://schemas.android.com/apk/res/android
        xmlns:tools=http://schemas.android.com/tools
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical" >
  3. Add a new checkbox view inside the linear layout. Give it a new id of vibrate_check, and set the layout_width and layout_height to wrap_content. Set a resource text to the value @string/vibrate_checkbox:
    <CheckBox
        android:id="@+id/vibrate_checkbox"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/vibrate_checkbox" />
  4. Add the new resource string vibrate_checkbox to the strings.xml file:

        <string name="vibrate_checkbox">Vibrate</string>

Showing a New Activity

To show a new activity, you first need to create an intent. Intents, in their simplest form, are a description of an activity that you want to occur. (You can also start activities in other applications, as covered later in the book.)

Next, you’ll create a new intent to display the Settings activity.

  1. Open the activity_timer layout. To launch the new activity, add a new button to the linear layout. Give the button an ID of settings_button, and a click handler to call the method clickedSettings when the button is pressed:

    <Button
        android:id="@+id/settings_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="@string/settings_button"
        android:onClick="clickedSettings" />
  2. Add the new resource string for the Settings button:

    <string name="settings_button">Settings</string>
  3. In the TimerActivity.java file, add a new clickedSettings method:

    public void clickedSettings(View view) {
        Log.d(CLASS_NAME, "clickedSettings");
    }
  4. Debug the application, and check that the clickedSettings call is logged in the LogCat view. If an RTE occurs, double-check that the onClick contains exactly the same method name as the new method just added.
  5. In the clickedSettings method, create a new Intent. Then pass the application context and the class property of the SettingsActivity. Run Quick fix to add the import statement for the Intent class:

    Intent settingsIntent = new Intent(getApplicationContext(),
        SettingsActivity.class);
  6. Display the new activity by calling startActivity, passing the intent you just created:

    startActivity(settingsIntent);
  7. Run the application again, and click the Settings button. The setting activity (displaying a checkbox) with a single checkbox will replace the timer activity, as shown in Figure 4.9.

    Figure 4.9

    Figure 4.9 The new Settings activity

Saving an Application’s State

Application state can be stored in many ways, either as static properties stored globally in the application or through the use of the singleton pattern. This pattern is designed to control object creation, limiting the number of objects to one. Because there is only ever one instance of the application class, you can use that to act as a singleton.

Here’s how to create a class to save and retrieve the application settings.

  1. Create a new Java class called Settings. Add a private static (of type String) CLASS_NAME, and assign the class name in the class constructor:

    public class Settings {
        private static String CLASS_NAME;
    
        public Settings() {
            CLASS_NAME = getClass().getName();
        }
    }
  2. Create a private property to store whether or not the vibrate setting is turned on:

    protected boolean vibrateOn;
  3. Create a method to return this property. Run Quick fix to import the Log class:

    public boolean isVibrateOn() {
        Log.d(CLASS_NAME, "isVibrateOn");
        return vibrateOn;
    }
  4. Create a method to set the value of the property:

    public void setVibrate(boolean vibrate) {
        Log.d(CLASS_NAME, "setVibrate");
        vibrateOn = vibrate;
    }
  5. Create a new class called OnYourBike that extends Application. Add a settings property of type Settings to this class:

    public class OnYourBike extends Application {
        protected Settings settings;
    }
  6. Add a method named getSettings that creates an instance of Settings if it hasn’t already been created, and return the settings property:

    public Settings getSettings() {
        if (settings == null) {
            settings = new Settings();
        }
        return settings;
    }
  7. Add a method named setSettings that changes the settings property to the settings value passed in:

    public void setSettings(Settings settings) {
        this.settings = settings;
    }
  8. Change the Android manifest file so that the application uses this class as its application by setting the android:name attribute to ".OnYourBike":

    <application android:name=".OnYourBike"
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
  9. Open SettingActivity.java, and add a vibrate checkbox property. Run Quick fix to import the CheckBox class:

    private CheckBox vibrate;
  10. In the onCreate method, after the call to setContentView, obtain access to the checkbox by calling findViewById:

    vibrate = (CheckBox)
        findViewById(R.id.vibrate_checkbox);
  11. Obtain the settings by calling the getSettings method just created:

    Settings settings = ((OnYourBike)getApplication()).getSettings();
  12. Just after that, set the state of the checkbox according to the setting:

    vibrate.setChecked(settings.isVibrateOn());
  13. Override the onStop method to save the settings:

    @Override
    public void onStop() {
        super.onStop();
        Settings settings = ((OnYourBike) getApplication()).getSettings();
        settings.setVibrate(vibrate.isChecked());
    }
    
  14. Run the application, click the Settings button, change the settings checkbox, and press the back button. Go back into the setting activity again by clicking the Settings button. The vibrate checkbox should still be ticked.

Notice that there was no need to add a handler to the checkbox for the state to be saved when the activity was stopped. Depending on how the activity is used in your application, you may want to save the setting right away rather than wait until the activity is stopped.

Using Shared Preferences

The settings class you created saves the application’s state only while it is running. If the application is stopped and restarted, it won’t remember the previous state. To fix that, you need to use shared preferences to save the application’s state. Shared preferences allow you to save key value pairs on a device.

You can save the vibration setting—whether it’s turned on or off—as a preference:

  1. Open Settings.java, and add a private static string called VIBRATE:

    private static String VIBRATE = "vibrate";
  2. In the isVibrateOn method, obtain an instance of shared preferences by calling activity.getPreferences:

    SharedPreferences preferences
         = activity.getPreferences(Activity.MODE_PRIVATE);

    Run Quick fix to import the SharedPreferences and Activity classes.

  3. Check whether the VIBRATE keys exist, and, if they do, set vibrateOn to be the saved value:

    if (preferences.contains(VIBRATE)) {
        vibrateOn = preferences.getBoolean(VIBRATE, false);
    }
  4. Change the isVibrateOn method to take a single parameter of type Activity:

    public boolean isVibrateOn(Activity activity)
  5. In the setVibrate method, after the existing code, save the vibrate property by getting access to the shared preferences, creating an editor, saving the property by calling putBoolean, and committing the changes by calling apply:

    SharedPreferences preferences
         = activity.getPreferences(Activity.MODE_PRIVATE);
    Editor editor = preferences.edit();
    editor.putBoolean(VIBRATE, vibrate);
    editor.apply();

    Run Quick fix to import the Editor class.

  6. Change the setVibrate method to take an additional parameter of type Activity:

    public void setVibrate(Activity activity, boolean vibrate)
  7. Open SettingsActivity.java, and fix the two errors by passing this to the isVibrateOn and setVibrate methods:

    vibrate.setChecked(settings.isVibrateOn(this));
    settings.setVibrate(this, vibrate.isChecked());
  8. Run the application, click Settings, check the vibrate checkbox, and press the back button. Click Menu, and select all apps. Select your application, and click force stop. Run the application again, and click the Settings button. The vibrate checkbox should still be checked.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020