ASP.NET Web PDF Document Viewer/Editor Control Library

We ve clearly made some progress with our Plane class, but we re not done yet. We have a read-only property for its Identifier. We can store the speed, which we can get and set using two different properties representing different units, using a const field for the conversion factor. And we know the direction, which will be either the Approach ing or the Leaving member of an enum. We still need to store the aircraft s position. According to the specification, we ve got two polar coordinates (an angle and a distance) for its position on the ground, and another value for its height above sea level. We re likely to need to do a lot of calculations based on this position information. Every time we want to create a function to do that, we d need three parameters per point, which seems overly complex. (And error-prone it d be all too easy to inadvertently pass two numbers from one position, and a third number from a different position.) It would be nicer if we could wrap the numbers up into a single, lightweight, 3D point type that we can think of in the same kind of way we do int or double a basic building block for other classes to use with minimum overhead. This is a good candidate for a value type.

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So far, we ve been building a class. When creating an instance of the class, we stored it in a named variable, as Example 3-24 shows.

Plane someBoeing777 = new Plane("BA0049"); someBoeing777.Direction = DirectionOfApproach.Approaching;

A point on the screen is represented by a QPoint object, and you can specify the x and y values for a point in the constructor. A point is usually not enough to draw something; to specify a point alongside a width and a height you can use the QRect class. The QRect constructor accepts an x value, a y value, and a width, followed by a height. Figure 7-3 shows a QRect and QPoint in a coordinate system.

We can define another variable with a different name, and store a reference to the same plane in that new variable, as shown in Example 3-25.

Plane theSameBoeing777ByAnotherName = someBoeing777;

If we change a property through one variable, that change will be visible through the other. Example 3-26 modifies our plane s Direction property through the second variable, but then reads it through the first variable, verifying that they really are referring to the same object.

When you browse to an Atlas-enabled application, two script libraries get downloaded to the client; these are Atlas.js for Internet Explorer and AtlasCompat.js for other browsers. These script libraries effectively bootstrap Atlas functionality on the client side. The ScriptManager control handles the rendering of these references on the page (as <script> tags), so you don t need to manually add them to your page.

There are two classes closely related to QPoint and QRect: QPointF and QRectF. They are equivaTip

theSameBoeing777ByAnotherName.Direction = DirectionOfApproach.Leaving; if (someBoeing777.Direction == DirectionOfApproach.Leaving) { Console.WriteLine("Oh, they are the same!"); }

As Shakespeare might have said, if only he d found his true vocation as a C# developer:

Assuming you like the smell of jet fuel. When we define a type using class, we always get this behavior our variables behave as references to an underlying object. We therefore call a type defined as a class a reference type.

lent, but operate on floating-point values. Almost all methods that accept a rectangle or point can accept either type of rectangle or point.

It s possible for a reference type variable to be in a state where it isn t referring to any object at all. C# has a special keyword, null, to represent this. You can set a variable to null, or you can pass null as an argument to a method. And you can also test to see if a field, variable, or argument is equal to null in an if statement. Any field whose type is a reference type will automatically be initialized to null before the constructor runs, in much the same way as numeric fields are initialized to zero.

The enum we declared earlier and the built-in numeric types (int, double) behave differently, though, as Example 3-27 illustrates.

int firstInt = 3; int secondInt = firstInt; secondInt = 4; if (firstInt != 4) { Console.WriteLine("Well. They're not the same at all."); }

If you add a ScriptManager control to a blank page and then execute the application, you ll see the following tag embedded in your page (in this case, it is running in debug mode) when running Internet Explorer: <script src="ScriptLibrary/Atlas/Debug/Atlas.js" type="text/javascript"> </script> And you ll see this one when running it in Firefox: <script src="ScriptLibrary/Atlas/Debug/AtlasCompat.js" type="text/javascript"> </script> <script src="ScriptLibrary/Atlas/Debug/Atlas.js" type="text/javascript"> </script>

When we assign firstInt to secondInt, we are copying the value. In this case, the variables hold the actual value, not a reference to a value. We call types that behave this way value types.

A line is the most basic shape that you can draw using a painter. A line that goes between two points is drawn by using the drawLine(QPoint,QPoint) method. If you want to join more points in one go, you can use the drawPolyline(QPoint*, int) method. The drawLines(QVector<QPoint>) method is also used to draw several lines at once, but the lines aren t continuous. The three methods are used in Listing 7-3 and the result is shown in Figure 7-4. In the listing, a pixmap is created and filled with white before a painter is created, and the pen is configured to draw black lines. The two vectors polyPoints and linePoints are initialized, where linePoints is calculated from shifting the polyPoints points 80 pixels to the right. You can shift the points by adding an offset QPoint to each QPoint, which adds the x and y values together separately.