Home > Articles

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

This chapter is from the book

Cursors

Cursors are what contain the result set of a query made against a database in Android. The Cursor class has an API that allows an app to read (in a type-safe manner) the columns that were returned from the query as well as iterate over the rows of the result set.

Reading Cursor Data

Once a cursor has been returned from a database query, an app needs to iterate over the result set and read the column data from the cursor. Internally, the cursor stores the rows of data returned by the query along with a position that points to the current row of data in the result set. When a cursor is returned from a query() method, its position points to the spot before the first row of data. This means that before any rows of data can be read from the cursor, the position must be moved to point to a valid row of data.

The Cursor class provides the following methods to manipulate its internal position:

  • boolean Cursor.move(int offset): Moves the position by the given offset

  • boolean Cursor.moveToFirst(): Moves the position to the first row

  • boolean Cursor.moveToLast(): Moves the position to the last row

  • boolean Cursor.moveToNext(): Moves the cursor to the next row relative to the current position

  • boolean Cursor.moveToPosition(int position): Moves the cursor to the specified position

  • Cursor.moveToPrevious(): Moves the cursor to the previous row relative to the current position

Each move() method returns a boolean to indicate whether the operation was successful or not. This flag is useful for iterating over the rows in a cursor.

Listing 5.10 shows the code to read data from a cursor containing all the data from the people table.

Listing 5.10 Reading Cursor Data

SQLiteDatabase db = getDatabase();

String[] columns = {"first_name",
        "last_name",
        "id"};

Cursor cursor = db.query("people",
        columns,
        null,
        null,
        null,
        null,
        null);

while(cursor.moveToNext()) {
    int index;

    index = cursor.getColumnIndexOrThrow("first_name");
    String firstName = cursor.getString(index);

    index = cursor.getColumnIndexOrThrow("last_name");
    String lastName = cursor.getString(index);

    index = cursor.getColumnIndexOrThrow("id");
    long id = cursor.getLong(index);

    //... do something with data
}

The code in Listing 5.10 uses a while loop to iterate over the rows in the cursor returned from the query() method. This pattern is useful if the code performing the iteration “controls” the cursor and has sole access to it. If other code can access the cursor (for example, if the cursor is passed into a method as a parameter), the cursor should also be set to a known position as the current position may not be the position ahead of the first row.

Once the cursor’s position is pointing to a valid row, the columns of the row can be read from the cursor. To read the data, the code in Listing 5.10 uses two methods from the cursor class: Cursor.getColumnIndexOrThrow() and one of the type get() methods from the Cursor class.

The Cursor.getColumnIndexOrThrow() method takes a String parameter that indicates which column to read from. This String value needs to correspond to one of the strings in the columns parameter that was passed to the query() method. Recall that the columns parameter determines what table columns are part of the result set. Cursor.getColumnIndexOrThrow()throws an exception if the column name does not exist in the cursor. This usually indicates that the column was not part of the columns parameter of the query(). The Cursor class also contains a Cursor.getColumnIndex() method that does not throw an exception if the column name is not found. Instead, Cursor.getColumnIndex() returns a -1 value to represent an error.

Once the column index is known, it can be passed to one of the cursor’s get() methods to return the typed data of the row. The get() methods return the data from the column in the row which can then be used by the app. The Cursor class contains the following methods for retrieving data from a row:

  • byte[] Cursor.getBlob(int columnIndex): Returns the value as a byte[]

  • double Cursor.getDouble(int columnIndex): Returns the value as a double

  • float Cursor.getFloat(int columnIndex): Returns the value as a float

  • int Cursor.getInt(int columnIndex): Returns the value as an int

  • long Cursor.getLong(int columnIndex): Returns the value as a long

  • short Cursor.getShort(int columnIndex): Returns the value as a short

  • String Cursor.getString(int columnIndex): Returns the value as a String

Managing the Cursor

The internals of a cursor can contain a lot of resources such as all the data returned from the query along with a connection to the database. Because of this, it is important to handle a cursor appropriately and tell it to clean up when it is no longer in use to prevent memory leaks. To perform the cleanup, the Cursor class contains the Cursor.close() method, which needs to be called when an activity or fragment no longer needs the cursor.

In versions of Android before 3.0, cursor maintenance was left to developers. They either had to handle the closing of the cursor themselves or had to make sure they informed an activity that it was using a cursor so the activity would close the cursor at an appropriate time.

Android 3.0 introduced the loader framework that takes care of managing cursors for activities/fragments. To support older versions of Android, the loader framework has also been backported and added to the support library. When using the loader framework, apps no longer need to worry about calling Cursor.close() or informing an activity/fragment of a cursor that it needs to manage.

  • + 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.

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