ASP.NET Web PDF Document Viewer/Editor Control Library

In the previous chapter, we saw how to define various types of classes and specify their members fields, properties, and functions. In this chapter, we re going to start by looking at this again in more detail, and try to understand what underlying concepts we re implementing when we use these different coding patterns. We ll then introduce a couple of new concepts inheritance and polymorphism and the language features that help us implement them. We ve finished our ATC application, by the way. Having gotten a reputation for building robust mission-critical software on time and to spec, we ve now been retained by the fire department to produce a training and simulation system for them. Example 4-1 shows what we have so far.

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class Firefighter { public string Name { get; set; } public void ExtinguishFire() { Console.WriteLine("{0} is putting out the fire!", Name); } public void Drive(Firetruck truckToDrive, Point coordinates) { if (truckToDrive.Driver != this) { // We can't drive the truck if we're not the driver // But just silently failing is BADBAD // What we need is some kind of structured means // of telling the client about the failure // We'll get to that in 6 return; } truckToDrive.Drive(coordinates); }

<atlas:ScriptManager ID="ScriptManager1" runat="server"> <ErrorTemplate> <div style="padding: 12px; width: 400px; height: 140px; border: #000000 1px solid;background-color: white; text-align: justify"> <span style="font-size: 10pt; font-family: Verdana"> <strong> Your application encountered an error. <br /> <br /> For support, please call the information hotline at (555) 555 1234. <br /> <span id="errorMessageLabel"> </span> <br /> You can also email us by clicking <a href="mailto:support@supporthotline.com">here</a>. <br /> <br /> </strong> </span> <input id="okButton" type="button" value="OK" style="font-weight: bold; font-size: 10pt; font-family: Verdana" /> <spanstyle="font-size: 10pt; font-family: Verdana"> </span> </div> </ErrorTemplate> </atlas:ScriptManager> To run an application that creates an error, you can add a button to the page. This button, when clicked, will trigger the error. First add a button: <asp:Button runat="server" ID="MyButton" Text="Click Me!" OnClick="MyButton_Click" /> When you click this button, you will call the MyButton_Click event. You define this using a server-side script: <script runat="server"> private void OnScriptManagerPageError(object sender, PageErrorEventArgs e) { e.ErrorMessage = "Please do not press that button again."; }

} class Firetruck { public Firefighter Driver { get; set; } public void Drive(Point coordinates) { if (Driver == null) { // We can't drive if there's no driver return; } } Console.WriteLine("Driving to {0}", coordinates);

Brushes are used to fill shapes and paths. Until now you used brushes to fill the designated areas using solid colors. This is only a part of what is possible. Using different patterns, gradients, or even textures, you can fill your shapes in any conceivable way. When you create a QBrush object, you can specify a color and a style. The constructor is defined as QBrush(QColor, Qt::BrushStyle). The QBrush is then given to a QPainter using the setBrush method. The style of the brush controls how the color is used when filling shapes. The simplest styles are patterns, which are used when you need to fill a shape with lines or a dithered shade. The available patterns and corresponding enumerated styles are shown in Figure 7-15.

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We have a model of the Firetruck, which uses a Firefighter as its Driver. The truck can be instructed to drive somewhere (if it has a driver), and you can tell a Firefighter to drive the truck somewhere (if he is the designated driver). You can think of this as modeling a relationship between a Firetruck and its Driver. That driver has to be a Firefighter. In object-oriented design, we call this relationship between classes an association.

An association is a kind of flexible, arms length relationship between two entities in the system. There are no particular constraints about the direction of the relationship: the firefighter can be associated with the truck, or the truck with the firefighter. Or both. Any particular firefighter may have associations with other types, and we can always assign another driver to the fire truck; there s no exclusivity. For instance, we can do something like this:

Firetruck truckOne = new Firetruck(); Firefighter joe = new Firefighter { Name = "Joe" }; Firefighter frank = new Firefighter { Name = "Frank" }; truckOne.Driver = joe; // Later... truckOne.Driver = frank;