Home > Articles > Mobile Application Development & Programming

  • Print
  • + Share This
This chapter is from the book

Handling User Events

You’ve seen how to do basic event handling in some of the previous control examples. For instance, you know how to handle when a user clicks on a button. There are a number of other events generated by various actions the user might take. This section briefly introduces you to some of these events. First, though, we need to talk about the input states in Android.

Listening for Touch Mode Changes

The Android screen can be in one of two states. The state determines how the focus on View controls is handled. When touch mode is on, typically only objects such as EditText get focus when selected. Other objects, because they can be selected directly by the user tapping on the screen, won’t take focus but instead trigger their action, if any. When not in touch mode, however, the user can change focus among even more object types. These include buttons and other views that normally need only a click to trigger their action.

Knowing what mode the screen is in is useful if you want to handle certain events. If, for instance, your application relies on the focus or lack of focus on a particular control, your application might need to know whether the device is in touch mode because the focus behavior is likely different.

Your application can register to find out when the touch mode changes by using the addOnTouchModeChangeListener() method in the android.view.ViewTreeObserver class. Your application needs to implement the ViewTreeObserver.OnTouchModeChangeListener class to listen for these events. Here is a sample implementation:

View all = findViewById(R.id.events_screen);
ViewTreeObserver vto = all.getViewTreeObserver();
    new ViewTreeObserver.OnTouchModeChangeListener() {
        public void onTouchModeChanged(
            boolean isInTouchMode) {
            events.setText("Touch mode: " + isInTouchMode);

In this example, the top-level View in the layout is retrieved. A ViewTreeObserver listens to a View and all its child View objects. Using the top-level View of the layout means the ViewTreeObserver listens to events in the entire layout. An implementation of the onTouchModeChanged() method provides the ViewTreeObserver with a method to call when the touch mode changes. It merely passes in which mode the View is now in.

In this example, the mode is written to a TextView named events. We use this same TextView in further event handling examples to show on the screen which events our application has been told about. The ViewTreeObserver can enable applications to listen to a few other events on an entire screen.

By running this sample code, we can demonstrate the touch mode changing to true immediately when the user taps on the touchscreen. Conversely, when the user chooses to use any other input method, the application reports that touch mode is false immediately after the input event, such as a key being pressed.

Listening for Events on the Entire Screen

You saw in the last section how your application can watch for changes to the touch mode state of the screen using the ViewTreeObserver class. The ViewTreeObserver also provides other events that can be watched for on a full screen or an entire View and all of its children. Some of these are:

  • Drawor PreDraw: Get notified before the View and its children are drawn.
  • GlobalLayout: Get notified when the layout of the View and its children might change, including visibility changes.
  • GlobalFocusChange: Get notified when the focus in the View and its children changes.

Your application might want to perform some actions before the screen is drawn. You can do this by calling the method addOnPreDrawListener() with an implementation of the ViewTreeObserver.OnPreDrawListener class interface or by calling the method addOnDrawListener() with an implementation of the ViewTreeObserver.OnDrawListener class interface.

Similarly, your application can find out when the layout or visibility of a View has changed. This might be useful if your application dynamically changes the display contents of a View and you want to check to see whether a View still fits on the screen. Your application needs to provide an implementation of the ViewTreeObserver.OnGlobalLayoutListener class interface to the addGlobalLayoutListener() method of the ViewTreeObserver object.

Finally, your application can register to find out when the focus changes between a View control and any of its child View controls. Your application might want to do this to monitor how a user moves about on the screen. When in touch mode, though, there might be fewer focus changes than when touch mode is not set. In this case, your application needs to provide an implementation of the ViewTreeObserver.OnGlobalFocusChangeListener class interface to the addGlobalFocusChangeListener() method.

Here is a sample implementation of this:

    ViewTreeObserver.OnGlobalFocusChangeListener() {
        public void onGlobalFocusChanged(
            View oldFocus, View newFocus) {
                if (oldFocus != null && newFocus != null) {
                    events.setText("Focus \nfrom: " +
                        oldFocus.toString() + " \nto: " +

This example uses the same ViewTreeObserver, vto, and TextView events as the previous example. It shows that both the currently focused View object and the previously focused View object are passed to the listener as method parameters. From here, your application can perform needed actions.

If your application merely wants to check values after the user has modified a particular View object, though, you might need to register to listen for focus changes only of that particular View object. This is discussed later in this chapter.

Listening for Long Clicks

You can add a context menu or a contextual action bar to a View that is activated when the user performs a long click on that View. A long click is typically when a user presses on the touchscreen and holds a finger there until an action is performed. However, a long press event can also be triggered if the user navigates there with a non-touch method, such as via a keyboard or a button. This action is also often called a press-and-hold action.

Although the context menu is a great typical use case for the long-click event, you can listen for the long-click event and perform any action you want. However, this is the same event that triggers the context menu. If you’ve already added a context menu to a View, you might not want to listen for the long-click event as other actions or side effects might confuse the user or even prevent the context menu or contextual action bar from showing. As always with good user interface design, try to be consistent for usability’s sake.

Your application can listen to the long-click event on any View. The following example demonstrates how to listen for a long-click event on a Button control:

Button long_press = (Button) findViewById(R.id.long_press);
long_press.setOnLongClickListener(new View.OnLongClickListener() {
    public boolean onLongClick(View v) {
        events.setText("Long click: " + v.toString());
        return true;

First, the Button object is requested by providing its identifier. Then the setOnLongClickListener() method is called with our implementation of the View.OnLongClickListener class interface. The View on which the user long-clicked is passed in to the onLongClick() event handler. Here again we use the same TextView as before to display text saying that a long click occurred.

Listening for Focus Changes

We have already discussed listening for focus changes on an entire screen. All View objects, though, can also trigger a call to listeners when their particular focus state changes. You do this by providing an implementation of the View.OnFocusChangeListener class to the setOnFocusChangeListener() method. The following is an example of how to listen for focus change events with an EditText control:

TextView focus = (TextView) findViewById(R.id.text_focus_change);
focus.setOnFocusChangeListener(new View.OnFocusChangeListener() {
    public void onFocusChange(View v, boolean hasFocus) {
        if (hasFocus) {
            if (mSaveText != null) {
        } else {
            mSaveText = ((TextView)v).getText().toString();

In this implementation, we also use a private member variable of type String for mSaveText. After retrieving the EditText control as a TextView, we do one of two things. If the user moves focus away from the control, we store the text in mSaveText and set the text to empty. If the user changes focus to the control, though, we restore this text. This has the amusing effect of hiding the text the user entered when the control is not active. This can be useful on a form on which a user needs to make multiple, lengthy text entries but you want to provide an easy way for the user to see which one to edit. It is also useful for demonstrating a purpose for the focus listeners on a text entry. Other uses might include validating text a user enters after the user navigates away or prefilling the text entry the first time the user navigates to it with something else entered.

  • + Share This
  • 🔖 Save To Your Account

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.


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.


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.


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.


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


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


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.


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.


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