Home > Articles > Programming > C#

Mastering XAML

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

Mixing XAML with Procedural Code

XAML-based Windows Store apps are a mix of XAML and procedural code. This section covers the two ways that XAML and code can be mixed together: dynamically loading and parsing XAML yourself, or leveraging the built-in support in Visual Studio projects.

Loading and Parsing XAML at Runtime

The Windows.UI.Xaml.Markup namespace contains a simple XamlReader class with a simple static Load method. Load can parse a string containing XAML, create the appropriate Windows Runtime objects, and return an instance of the root element. So, with a string containing XAML content somewhat like MainPage.xaml from the preceding chapter, the following code could be used to load and retrieve the root Page object:

string xamlString = ...;
// Get the root element, which we know is a Page
Page p = (Page)XamlReader.Load(xamlString);

After Load returns, the entire hierarchy of objects in the XAML file is instantiated in memory, so the XAML itself is no longer needed. Now that an instance of the root element exists, you can retrieve child elements by making use of the appropriate content properties or collection properties. The following code assumes that the Page has a StackPanel object as its content, whose fifth child is a Stop button:

string xamlString = ...;
// Get the root element, which we know is a Page
Page p = (Page)XamlReader.Load(xamlString);
// Grab the Stop button by walking the children (with hard-coded knowledge!)
StackPanel panel = (StackPanel)p.Content;
Button stopButton = (Button)panel.Children[4];

With a reference to the Button control, you can do whatever you want: Set additional properties (perhaps using logic that is hard or impossible to express in XAML), attach event handlers, or perform additional actions that you can’t do from XAML, such as calling its methods.

Of course, the code that uses a hard-coded index and other assumptions about the user interface structure isn’t satisfying, because simple changes to the XAML can break it. Instead, you could write code to process the elements more generically and look for a Button element whose content is a "Stop" string, but that would be a lot of work for such a simple task. In addition, if you want the Button to contain graphical content, how can you easily identify it in the presence of multiple Buttons?

Fortunately, XAML supports naming of elements so they can be found and used reliably from procedural code.

Naming XAML Elements

The XAML language namespace has a Name keyword that enables you to give any element a name. For the simple Stop button that we’re imagining is embedded somewhere inside a Page, the Name keyword can be used as follows:

<Button x:Name="stopButton">Stop</Button>

With this in place, you can update the preceding C# code to use Page’s FindName method that searches its children (recursively) and returns the desired instance:

string xamlString = ...;
// Get the root element, which we know is a Page
Page p = (Page)XamlReader.Load(xamlString);
// Grab the Stop button, knowing only its name
Button stopButton = (Button)p.FindName("stopButton");

FindName is not unique to Page; it is defined on FrameworkElement, a base class for many important classes in the XAML UI Framework.

Visual Studio’s Support for XAML and Code-Behind

Loading and parsing XAML at runtime can be interesting for some limited dynamic scenarios. Windows Store projects, however, leverage work done by MSBuild and Visual Studio to make the combination of XAML and procedural code more seamless. When you compile a project with XAML files, the XAML is included as a resource in the app being built and the plumbing that connects XAML with procedural code is generated automatically.

The automatic connection between a XAML file and a code-behind file is enabled by the Class keyword from the XAML language namespace, as seen in the preceding chapter. For example, MainPage.xaml had the following:

<Page x:Class="BlankApp.MainPage" ...>
  ...
</Page>

This causes the XAML content to be treated as a partial class definition for a class called MainPage (in the BlankApp namespace) derived from Page. The other pieces of the partial class definition reside in auto-generated files as well as the MainPage.xaml.cs code-behind file. Visual Studio’s Solution Explorer ties these two files together by making the code-behind file a subnode of the XAML file, but that is an optional cosmetic effect enabled by the following XML inside of the .csproj project file:

<Compile Include="MainPage.xaml.cs">
  <DependentUpon>MainPage.xaml</DependentUpon>
</Compile>

You can freely add members to the class in the code-behind file. And if you reference any event handlers in XAML (via event attributes such as Click on Button), this is where they should be defined.

Whenever you add a page to a Visual Studio project (via Add New Item...), Visual Studio automatically creates a XAML file with x:Class on its root, creates the code-behind source file with the partial class definition, and links the two together so they are built properly.

The additional auto-generated files alluded to earlier contain some “glue code” that you normally never see and you should never directly edit. For a XAML file named MainPage.xaml, they are:

  • MainPage.g.cs, which contains code that attaches event handlers to events for each event attribute assigned in the XAML file.
  • MainPage.g.i.cs, which contains a field definition (private by default) for each named element in the XAML file, using the element name as the field name. It also contains an InitializeComponent method that the root class’s constructor must call in the code-behind file. This file is meant to be helpful to IntelliSense, which is why it has an “i” in its name.

The “g” in both filenames stands for generated. Both generated source files contain a partial class definition for the same class partially defined by the XAML file and code-behind file.

If you peek at the implementation of InitializeComponent inside the auto-generated file, you’ll see that the hookup between C# and XAML isn’t so magical after all. It looks a lot like the code shown previously for manually loading XAML content and grabbing named elements from the tree of instantiated objects. Here’s what the method looks like for the preceding chapter’s MainPage if a Button named stopButton were added to it:

public void InitializeComponent()
{
  if (_contentLoaded)
    return;

  _contentLoaded = true;
  Application.LoadComponent(this, new System.Uri("ms-appx:///MainPage.xaml"),
    Windows.UI.Xaml.Controls.Primitives.ComponentResourceLocation.Application);

  stopButton = (Windows.UI.Xaml.Controls.Button)this.FindName("stopButton");
}

The LoadComponent method is much like XamlReader’s Load method, except it works with a reference to an app’s resource file.

  • + 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