ASP.NET PDF Viewer using C#, VB/NET

Figure 6-7. Promoting a QLabel to a ClockWidget To be able to use this feature of Designer, you must provide a constructor taking a QWidget pointer and make the include file accessible for the make system. This can be done with the INCLUDEPATH variable in the QMake project file. It is important to pick a widget that is in your custom widget s inheritance tree to make sure that all properties shown in Designer are available for your widget. The user interface compiler generates code for setting all properties marked as bold in Designer. In the property box shown in Figure 6-8, the properties objectName, geometry, text, and flat will be set. This means that if you promote the widget, your widget needs to have the setObjectName, setGeometry, setText, and setFlat methods. If you choose to promote a widget from the inheritance tree of your custom widget, you get these methods free through inheritance.

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for code that runs on an ARM-based handheld device to run unmodified on Intel-based PCs, or on the PowerPC architecture found in the Xbox 360 game console As interesting as CPU independence may be, in practice the most useful aspect of managed code and IL is that the NET runtime can provide useful services that are very hard for traditional compilation systems to implement well In other words, the point is to make developers more productive The memory management mentioned earlier is just one example.

On the Toolbox, if you right-click, you will find an option called Add Tab (see Figure 6-2). Selecting this adds a new tab to the Toolbox. This tab has a text box where you can type in a new title. Call the tab Atlas, and you will see a new, empty tab with no controls in it (see Figure 6-3). To populate this tab with the suite of Atlas server controls, right-click it, and select Choose Items, which opens the dialog box shown in Figure 6-4. It may take a few moments if it is the first time you ve done this, because the dialog box will be evaluating all the references and type libraries for the .NET and COM controls. Make sure the .NET Framework Components tab is selected.

Others include a security model that takes the origin of code into account rather than merely the identity of the user who happens to be running the code; flexible mechanisms for loading shared components with robust support for servicing and versioning; runtime code optimization based on how the code is being used in practice rather than how the compiler guesses it might be used; and as already mentioned, the CLR s ability to verify that code conforms to type safety rules before executing it, ruling out whole classes of security and stability bugs If you re a Java developer, all of this will sound rather familiar just substitute bytecode for IL and the story is very similar Indeed, a popular but somewhat ignorant joke among the less thoughtful members of the Java community is to describe C# as a poor imitation of Java.

When the first version of C# appeared, the differences were subtle, but the fact that Java went on to copy several features from C# illustrates that C# was always more than a mere clone The languages have grown more obviously different with each new version, but one difference, present from the start, is particularly important for Windows developers: C# has always made it easy to get at the features of the underlying Windows platform..

A field is a place to put some data of a particular type. There s no option to add code like you can in a property a field is nothing more than data. Back before C# 3.0 the compiler didn t let us write just get; and set; we always had to write properties with code as in Example 3-9, and if we wanted a simple property that stored a value, we had to provide a field, with code such as Example 3-12.

If you spend slightly more time implementing a plugin that works in Designer, you can skip the promotion method in Designer. Instead your widget will appear in the widget box with all the other widgets. Creating a widget plugin for Designer is pretty much a copy-and-paste job. Before you can start creating the plugin, you must make a small change to the widget class declaration. (For the plugin, you ll use the CircleBar widget developed earlier in this chapter.) The class declaration is shown in Listing 6-25. The first half of the change is the addition of the QDESIGNER_ WIDGET_EXPORT macro, which ensures that the class is available from the plugin on all platforms that Qt supports. The other half is the addition of a constructor taking a parent as argument. This is needed for the generated code from uic to work.

// Field to hold the SpeedInMilesPerHour property's value double speedInMilesPerHourValue; public double SpeedInMilesPerHour { get { return speedInMilesPerHourValue; } set { speedInMilesPerHourValue = value; } }