What Does Initializecomponent() Do, and How Does It Work in Wpf

What does InitializeComponent() do, and how does it work in WPF?

The call to InitializeComponent() (which is usually called in the default constructor of at least Window and UserControl) is actually a method call to the partial class of the control (rather than a call up the object hierarchy as I first expected).

This method locates a URI to the XAML for the Window/UserControl that is loading, and passes it to the System.Windows.Application.LoadComponent() static method. LoadComponent() loads the XAML file that is located at the passed in URI, and converts it to an instance of the object that is specified by the root element of the XAML file.

In more detail, LoadComponent creates an instance of the XamlParser, and builds a tree of the XAML. Each node is parsed by the XamlParser.ProcessXamlNode(). This gets passed to the BamlRecordWriter class. Some time after this I get a bit lost in how the BAML is converted to objects, but this may be enough to help you on the path to enlightenment.

Note: Interestingly, the InitializeComponent is a method on the System.Windows.Markup.IComponentConnector interface, of which Window/UserControl implement in the partial generated class.

Hope this helps!

Very Simple definition of InitializeComponent(); Method

InitializeComponent is a method automatically written for you by the Form Designer when you create/change your forms.

Every Forms file (e.g. Form1.cs) has a designer file (e.g. Form1.designer.cs) that contains the InitializeComponent method, the override of the generic Form.Dispose, and the declaration of all of your User Interface objects like buttons, textboxes, labels and the Form itself.

The InitializeComponent method contains the code that creates and initializes the user interface objects dragged on the form surface with the values provided by you (the programmer) using the Property Grid of the Form Designer. Due to this fact do not ever try to interact with the form or the controls before the call to InitializeComponent.

Also, you will find here, the plumbing required to link the controls and form events to the specific event handlers you have written to respond to the user actions.

The code contained in Form1.cs and the Form1.Designer.cs files is part of the same class thanks to the concept of partial classes that could keep two or more files of your code together like a single block of code.

Of course, due to the high numbers of changes executed by the Form Designer, it is a really good advice to not try to modify manually this method, while, sometime, I find useful to add code to the Dispose method with the purpose to destroy some unmanaged objects created in the form lifetime.

Why InitializeComponent is public

InitializeComponent is a method defined on the interface System.Windows.Markup.IComponentConnector and is used for loading the compiled page of a component.

See MSDN excerpt below from this link which has more info:

IComponentConnector is used internally by Baml2006Reader.

Implementations of InitializeComponent are widely observable as part of the infrastructure provided by frameworks or technologies that use XAML combined with application and programming models. For example, whenever you look at the generated classes for XAML root elements in WPF pages and applications, you will see InitializeComponent defined in the output. That method also exists in the compiled assembly and plays a role in the WPF application model of loading the XAML UI content at XAML parse time (and I suppose hence InitializeComponent has to be in an interface and be public so that other outside WPF related assemblies can make use of it).

To explain this further, go to the definition of InitializeComponent() method in your (say): Window1.g.cs class of say: WPFProject project, and change its access from public to private

(keep the .g.cs file open in your project otherwise the build process
overrides this file, and you won't be able to see the error)

Now, when you compile your WPF project, it throws a compile error as below:

Error 22 'WPFProject.Window1' does not implement interface member
'System.Windows.Markup.IComponentConnector.InitializeComponent()'.
'WPFProject.Window1.InitializeComponent()' cannot implement an
interface member because it is not public.

Additionally, InitializeComponent() is marked with the [System.Diagnostics.DebuggerNonUserCodeAttribute()] attribute so you can't step into this method while debugging.

There is another SO QA discussion, which would help you to explain more in detail

Why can't Visual Studio find my WPF InitializeComponent method?

Looks like this was a kink in Visual Studio 2008.

If I create a new file (i.e. Title2), copy/paste the code and XAML, then change all 'Title' to 'Title2', everything works fine again.

C# WPF Visibility of a TextBox in window constructor?

All references to named controls in XAML must be done after a call to InitializeComponent(). Whether that's on the constructor or not is up to you

In a constructor for a WPF Window, what should go before InitializeComponent() and what after?

By calling InitializeComponents after some other code you run the risk of accidentally overwriting properties with things that were set in the XAML or of using an uninitialized object. Usually the code-behind is a higher priority than the XAML so I would leave InitializeComponents (aka, parse and load the XAML) at the top.

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