.NET/ASP.NET/C#/VB.NET PDF Document SDK

After you have created a widget of your own, you might want to integrate it with Designer. The benefit of doing this is that you are not forced to leave the Designer workflow because you are using custom widgets. Another advantage is that if you develop widgets for others, you can let them use Designer with your widgets as well as standard Qt widgets. There are two approaches to integrating widgets with designer: one simple and one complex. Comparing the two methods, the simple method leaves more work to do when using Designer, while the complex method makes the integration with Designer seamless. Let s start out with the simple approach.

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DateTimeOffset tmo = GetTimeFromSomewhere(); DateTime localDateTime = tmo.ToLocalTime().DateTime;

There are two benefits to this. First, this gets the time into a representation likely to align with how end users normally think of times, that is, relative to whatever time zone they re in right now. Second, DateTime makes formatting slightly easier than DateTimeOffset: DateTimeOffset supports the same ToString formats as DateTime, but DateTime offers some additional convenient methods. First, DateTime offers an overload of the ToString method which can accept a range of standard format strings. Some of the more popular ones (such as d, the short date format, and D, the long date format) are also exposed as methods. Example 10-33 illustrates this.

DateTime time = new DateTime(2001, 12, 24, 13, 14, 15, 16); Console.WriteLine(time.ToString("d")); Console.WriteLine(time.ToShortDateString()); Console.WriteLine(time.ToString("D")); Console.WriteLine(time.ToLongDateString());

You can test the promotion way of integrating your widgets with Designer using the ClockWidget that you created earlier in this chapter. Because it is based on a QLabel, draw a QLabel on the form you are designing. Now bring up the context menu for the label and choose the Promote to Custom Widget menu entry, which brings up the dialog shown in Figure 6-7. The figure has a class name the header file name is automatically guessed by Designer.

This produces:

The .NET Framework provides more than just a class library. It also provides services in subtler ways that are not accessed explicitly through library calls. For example, earlier we mentioned that C# can automate some aspects of memory management, a notorious source of bugs in C++ code. Abandoning heap-allocated objects once you re done with them is a coding error in C++, but it s the normal way to free them in .NET. This service is provided by the CLR the .NET Framework s runtime environment. Although the C# compiler works closely with the runtime to make this possible, providing the necessary information about how your code uses objects and data, it s ultimately the runtime that does the work of garbage collection. Depending on what sorts of languages you may have worked with before, the idea that the language depends heavily on the runtime might seem either completely natural or somewhat disconcerting. It s certainly different from how C and C++ work with those languages, the compiler s output can be executed directly by the computer, and although those languages have some runtime services, it s possible to write code that can run without them. But C# code cannot even execute without the help of the runtime. Code that depends entirely on the runtime is called managed code. Managed compilers do not produce raw executable code. Instead, they produce an intermediate form of code called IL, the Intermediate Language. The runtime decides exactly how to convert it into something executable. One practical upshot of managed code is that a compiled C# program can run on both 32-bit and 64-bit systems without modification, and can even run on different processor architectures it s often possible

* VB.NET supports XML literals. Since C# 2.0 shipped, the C# and VB.NET teams have operated a policy of keeping the feature sets of the two languages similar, so the fact that VB.NET picked up a feature that C# abandoned shows a clear difference in language philosophy. Depending on whether you read Microsoft s documentation, or the ECMA CLI (Common Language Infrastructure) specifications that define the standardized parts of .NET and C#, IL s proper name is either MSIL (Microsoft IL) or CIL (Common IL), respectively. The unofficial name, IL, seems more popular in practice.