.NET/Java PDF, Tiff, Barcode SDK Library

Using Qt you can draw on almost anything: widgets, pictures, pixmaps, images, printers, OpenGL areas, and so on. The common base class of all these drawables is the QPaintDevice class. Since a widget is a paint device, you can easily create a QPainter for drawing onto the widget; simply pass this as argument to the constructor, as shown in Listing 7-1. Listing 7-1. Pass this as argument to the QPainter constructor from a paint event handler to set everything up. void CircleBar::paintEvent( QPaintEvent *event ) { ... QPainter p( this ); ... } To set up a painter for another paint device, just pass a pointer to it to the painter constructor. Listing 7-2 shows how a painter for a pixmap is set up. The pixmap that is 200 pixels wide and 100 pixels high is created. The painter for drawing on the pixmap is then created, and a pen and a brush are set up. Pens are used to draw the boundary of whatever shape you are drawing. Brushes are used to fill the interior of the shape. Before continuing, you need to know what a pixmap is and how it is different from an image or a picture. There are three major classes for representing graphics in Qt: QPixmap is optimized for being shown onscreen, QImage is optimized for loading and saving images, and QPicture records painter commands and makes it possible to replay them later.

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But there s one problem: if our Direction property s type is int, there s nothing to stop us from saying something like:

someBoeing777.Direction = 72;

This designer allows you to visually set up partial rendering, which is a tag that enables partial-page updates and is specified in UpdatePanel controls; this designer also allows you to create error templates and manage other ScriptManager templates. You ll be seeing more about these features throughout this chapter. Now, if you take a look at the code behind this .aspx page, you will see that placing the ScriptManager control has led to the following script being added to the page: <atlas:ScriptManager ID="ScriptManager1" runat="server"> </atlas:ScriptManager> When you run the page, you ll see the following source code when you select the View Source command in the browser: <script src="ScriptLibrary/Atlas/Debug/Atlas.js" type="text/javascript"></script> <div> </div> <script type="text/xml-script">

This makes no sense, but the C# compiler doesn t know that after all, we told it the property s type was int, so how s it supposed to know that s wrong Fortunately, the designers of C# have thought of this, and have given us a kind of type for precisely this situation, called an enum, and it turns out to be a much better solution for this than const int.

When targeting Unix and X11, the QPixmap class is optimized for showing only onscreen. It can even Tip

The enum keyword lets us define a type whose values can be one of a fixed set of possibilities. Example 3-21 declares an enum for our Direction property. You can add this to an existing source file, above or below the Plane class, for example. Alternatively, you could add a whole new source file to the project, although Visual Studio doesn t offer a file template for enum types, so either you d have to add a new class and then change the class keyword to enum, or you could use the Code File template to add a new, empty source file.

enum DirectionOfApproach { Approaching, Leaving }

This is similar in some respects to a class declaration. We can optionally begin with a protection level but if, like Example 3-21, we omit that, we get internal protection by default. Then there s the enum specifier itself, followed by the name of the type, which by convention we PascalCase. Inside the braces, we declare the members, again using PascalCasing. Notice that we use commas to separate the list of constants this is where the syntax starts to part company with class. Unusually, the members are publicly accessible by default. That s because an enum has no behavior, and so there are no implementation details it s just a list of named values, and those need to be public for the type to serve any useful purpose.

It s short for enumeration, by the way. So it s often pronounced e-noom or, depending on where you re from, e-nyoom. However, some developers (and one of the authors) ignore the etymology and pronounce it ee numb because that s how it looks like it should sound.

be stored on the X server (handing the screen), meaning less communication between the application and the X server.

Notice that we ve chosen to call this DirectionOfApproach, and not the plural DirectionsOfApproach. By convention, we give enum types a singular name even though they usually contain a list. This makes sense because when you use named entries from an enumeration, you use them one at a time, and so it would look odd if the type name were plural. Obviously, there won t be any technical consequences for breaking this convention, but following it helps make your code consistent with the .NET Framework class libraries.

We can now declare our Direction property, using the enumeration instead of an integer. Example 3-22 shows the property to add to the Plane class.

<page xmlns:script="http://schemas.microsoft.com/xml-script/2005"> <components /> </page></script> <script type="text/javascript"> </script> In this case, at runtime, ASP .NET renders the server-side control as a number of statements. The first is a reference to the script library Atlas.js, which will get downloaded automatically. Next is a <script> tag containing any client-side Atlas Script for the page components. Finally, another script tag appears for any JavaScript you may want to use on the page, such as custom actions or transforms.

public DirectionOfApproach Direction { get; set; }