Introduction
Windows Presentation Foundation (WPF) is yet another fiery hell software developers have to experience from Microsoft. Yet the flame is so beautiful I have to look through each spark.
Main WPF Application
A template provided by Visual Studio 2008, these files are created. These are files created inside the WPF application project file.
App.xaml And App.xaml.cs
The main entry of a typical WPF Application. WPF UI can be instantiated by the usual Main() method when the application is standalone, but App.xaml and its App.xaml.cs code-behind is required for application run in XAML browser applications and it is a standard signature for a WPF application. There must be one Application class created per AppDomain. Description of the main application can be done in the code-behind or in XAML.
x:Class="WPFApplication.App"
Given namespace WPFApplication and class name App that inherits from Application, x:Class points to the code-behind of App.xaml
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" provides the default XML namespace. This convention is similar to the old using statement.
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" provides additional XML namespace.
StartupURI
It's Application attribute that points to a UI that is automatically shown when an application starts.