Home > Articles

This chapter is from the book

This chapter is from the book

So far the discussion has focused on the properties implemented by a control for itself. TimeZoneModifier, an example of such a property, allows the clock control to be configured to display the time in any time zone. One way to use this feature is to display the time in each time zone where your organization has offices. If each office were visually represented with a picture box, you could drag one clock control for each time zone onto the form, manually adjusting the TimeZoneModifier property on each clock control. The result might look like Figure 9.15.

09fig15.gifFigure 9.15. Form with Multiple Time Zones




This works quite nicely but could lead to real estate problems, particularly if you have one clock control for each of the 24 time zones globally and, consequently, 24 implementations of the same logic on the form. If you are concerned about resources, this also means 24 system timers. Figure 9.16 shows what this might look like.

09fig16.gifFigure 9.16. One Provider Control for Each Client Control




Another approach is to have a single clock control and update its TimeZoneModifier property with the relevant time zone from the Click event of each picture box. This is a cumbersome approach because it requires developers to write the code associating a time zone offset with each control, a situation controls are meant to help avoid. Figure 9.17 illustrates this approach.

09fig17.gifFigure 9.17. One Provider Control for All Client Controls, Accessed with Code




A nicer way to handle this situation is to provide access to a single implementation of the clock control without forcing the developer to write additional property update code. .NET offers extender property support to do just this, allowing components to extend property implementations to other components.

Logically, an extender property is a property provided by an extender component, like the clock control, on other components in the same container, like picture boxes. Extender properties are useful whenever a component needs data from a set of other components in the same host. For example, WinForms itself provides several extender components, including ErrorProvider, HelpProvider, and ToolTip. In the case of the ToolTip component, it makes a lot more sense to set the ToolTip property on each control on a form than it does to try to set tooltip information for each control using an editor provided by the ToolTip component itself.

In our case, by implementing TimeZoneModifier as an extender property, we allow each picture box control on the form to get its own value, as shown in Figure 9.18.

09fig18.gifFigure 9.18. One Provider Control for All Client Controls, Accessed with a Property Set




Exposing an extender property from your control requires that you first use ProvidePropertyAttribute to declare the property to be extended:

[ProvidePropertyAttribute("TimeZoneModifier", typeof(PictureBox))]
   public class ClockControl : Control { ... }
   

The first parameter to the attribute is the name of the property to be extended. The second parameter is the "receiver" type, which specifies the type of object to extend, such as PictureBox. Only components of the type specified by the receiver can be extended. If you want to implement a more sophisticated algorithm, such as supporting picture boxes and panels, you must implement the IExtenderProvider CanExtend method:

class ClockControl : ..., IExtenderProvider {
   bool IExtenderProvider.CanExtend(object extendee) {
   // Don't extend self
   if( extendee == this ) return false;
   
   // Extend suitable controls
   return( (extendee is PictureBox) ||
   (extendee is Panel) );
   }
   ...
   }
   

As you saw in Figure 9.18, the provider supports one or more extendee controls. Consequently, the provider control must be able to store and distinguish one extendee's property value from that of another. It does this in the Get<PropertyName> and Set<PropertyName> methods, in which PropertyName is the name you provided in ProvidePropertyAttribute. Then GetTimeZoneModifier simply returns the property value when requested by the Property Browser:

public class ClockControl : Control, IExtenderProvider {
  // Mapping of components to numeric timezone offsets
   HashTable timeZoneModifiers = new HashTable();
   
   public int GetTimeZoneModifier(Control extendee) {
   // Return component's timezone offset
   return int.Parse(timeZoneModifiers[extendee]);
   }
   ...
   }
   

SetTimeZoneModifier has a little more work to do. Not only does it put the property value into a new hash table for the extendee when provided, but it also removes the hash table entry when the property is cleared. Also, with the sample TimeZoneModifier property, you need to hook into each extendee control's Click event, unless the control isn't using the extender property. SetTimeZoneModifier is shown here:

class ClockControl : ..., IExtenderProvider {
  HashTable timeZoneModifiers = new HashTable();
   ...
   public void SetTimeZoneModifier(Control extendee, object value) {
   // If property isn't provided
   if( value == null ) {
   // Remove it
   timeZoneModifiers.Remove(extendee);
   if( !this.DesignMode ) {
   extendee.Click -= new EventHandler(extendee_Click);
   }
   }
   else {
   // Add the offset as an integer
   timeZoneModifiers[extendee] = int.Parse(value);
   if( !this.DesignMode ) {
   extendee.Click += new EventHandler(extendee_Click);
   }
   }
   }
   }
   

As with other properties, you can affect the appearance of an extender property in the Property Browser by adorning the Get<PropertyName> method with attributes:

class ClockControl : ..., IExtenderProvider {
  [
   Category("Behavior"),
   Description("Sets the timezone difference from the current time"),
   DefaultValue("")
   ]
   public int GetTimeZoneModifier(Control extendee) { ... }
   ...
   }
   

These attributes are applied to the extendee's Property Browser view.

With all this in place, you can compile your extender component to see the results. Extended properties will appear in the extendee component's properties with the following naming format:

<ExtendedPropertyName> on <ExtenderProviderName>

Figure 9.19 shows the TimeZoneModifier extender property behaving like any other property on a PictureBox control.

09fig19.gifFigure 9.19. Extended Property in Action




If a property is set and is not the default value, it is serialized to InitializeComponent(), as a SetTimeZoneModifier method call, and grouped with the extendee component:

void InitializeComponent() {
  ...
  this.clockControl1.SetTimeZoneModifier(this.pictureBox1, -11);
   ...
   }
   

Extender properties allow a component to add to the properties of other components in the same host. In this way, the developer can keep the data with the intuitive component, which is not necessarily the component that provides the service.

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