A 2D Graphics Test Bed - Computer Graphics: Principles and Practice - page 84

The highest-level portion of the application is called Testbed2DApp ;
it is implemented in the files Testbed2DApp.xaml (the XAML file) and
Testbed2DApp.xaml.cs (the associated C# file).
The XAML file (see Listing 4.1) declares that Testbed2D is an object of class
Application , which means that it has certain properties, events, and methods pre-
defined; we use almost none of these, with the exception of the Startup event
handler, which we'll see in the C# file. 1

Listing 4.1: The code in Testbed2DApp.xaml .

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<Application x:Class= "Testbed2D.Testbed2DApp"
xmlns= "http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x= "http://schemas.microsoft.com/winfx/2006/xaml"
Startup= "AppStartingUp" >
<Application.Resources />
</Application>

The code in Listing 4.1 simply declares an application and some infor-
mation about where to find certain name resolutions (the xmlns lines) for
this XML namespace. The key element, from our point of view, is the line
Startup= "AppStartingUp" , which says that the Startup event is to be handled by
code that will be found in the AppStartingUp method of the Testbed2D.xaml.cs
file. This is the equivalent of main() in a C++ or Java program.
The corresponding C# file is shown in Listing 4.2. The keyword partial tells
us that part of the class's description is here, but part of it is elsewhere (in the
XAML file). The AppStartingUp method has been defined to create a Window1
and to show it. The arguments to AppStartingUp are unused. The remaining event
handlers, methods, etc., for the Testbed2DApp remain unchanged from the defaults
inherited from the Application class.

Listing 4.2: The corresponding C# file, Testbed2DApp.xaml.cs .

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using System;
using ...

namespace Testbed2D
{

public partial class Testbed2DApp : Application
{

void AppStartingUp( object sender, StartupEventArgs e)
{

Window1 mainWindow = new Window1();
mainWindow.Show();

}

}

}

So, if we run the Testbed2DApp , upon startup a Window1 will be created and
shown.
This Window1 class is somewhat richer than the Testbed2DApp class: It corre-
sponds to the main window of a conventional application and includes things like

1. Other events are things like OnExit , which occurs when the program exits, and
Activated , which occurs when the application becomes the foreground application;
all the details of every class in WPF are documented online, but part of the goal in the
test bed is to shield you from having to know most of them.