qr code c# asp.net The Conditional Attribute in Visual C#

Drawing QR Code JIS X 0510 in Visual C# The Conditional Attribute

The Conditional Attribute
Quick Response Code Drawer In C#
Using Barcode generation for .NET Control to generate, create QR Code ISO/IEC18004 image in .NET applications.
QR Code Recognizer In C#.NET
Using Barcode decoder for Visual Studio .NET Control to read, scan read, scan image in Visual Studio .NET applications.
The attribute Conditional is perhaps C# s most interesting built-in attribute It allows you to create conditional methods A conditional method is invoked only when a specific symbol has been defined via #define Otherwise, the method is bypassed Thus, a conditional method offers an alternative to conditional compilation using #if Conditional is another name for SystemDiagnosticsConditionalAttribute To use the Conditional attribute, you must include the SystemDiagnostics namespace
Bar Code Generator In C#
Using Barcode drawer for Visual Studio .NET Control to generate, create barcode image in .NET applications.
Read Barcode In Visual C#
Using Barcode decoder for .NET Control to read, scan read, scan image in VS .NET applications.
Part I:
Paint QR Code In .NET
Using Barcode generator for ASP.NET Control to generate, create Denso QR Bar Code image in ASP.NET applications.
Creating Denso QR Bar Code In .NET Framework
Using Barcode printer for VS .NET Control to generate, create QR image in .NET applications.
The C# Language
Make QR Code ISO/IEC18004 In VB.NET
Using Barcode maker for VS .NET Control to generate, create Quick Response Code image in .NET applications.
EAN 13 Generator In Visual C#.NET
Using Barcode maker for Visual Studio .NET Control to generate, create GTIN - 13 image in Visual Studio .NET applications.
Let s begin with an example:
Printing ECC200 In C#.NET
Using Barcode creation for Visual Studio .NET Control to generate, create Data Matrix 2d barcode image in Visual Studio .NET applications.
Code 128 Code Set B Generator In C#
Using Barcode maker for Visual Studio .NET Control to generate, create USS Code 128 image in .NET framework applications.
// Demonstrate the Conditional attribute #define TRIAL using System; using SystemDiagnostics; class Test { [Conditional("TRIAL")] void Trial() { ConsoleWriteLine("Trial version, not for distribution"); } [Conditional("RELEASE")] void Release() { ConsoleWriteLine("Final release version"); } static void Main() { Test t = new Test(); tTrial(); // called only if TRIAL is defined tRelease(); // called only if RELEASE is defined } }
Generating Matrix 2D Barcode In C#.NET
Using Barcode maker for VS .NET Control to generate, create 2D Barcode image in VS .NET applications.
Creating C 2 Of 5 In Visual C#.NET
Using Barcode encoder for VS .NET Control to generate, create Standard 2 of 5 image in .NET applications.
The output from this program is shown here:
Encode Barcode In Objective-C
Using Barcode encoder for iPhone Control to generate, create barcode image in iPhone applications.
Drawing Code 128B In Java
Using Barcode generator for Java Control to generate, create Code128 image in Java applications.
Trial version, not for distribution
EAN / UCC - 13 Drawer In Java
Using Barcode creation for Android Control to generate, create EAN128 image in Android applications.
USS Code 39 Encoder In Java
Using Barcode drawer for Android Control to generate, create Code 39 image in Android applications.
Let s look closely at this program to understand why this output is produced First, notice the program defines the symbol TRIAL Next, notice how the methods Trial( ) and Release( ) are coded They are both preceded with the Conditional attribute, which has this general form: [Conditional symbol] where symbol is the symbol that determines whether the method will be executed If the symbol is defined, then when the method is called, it will be executed If the symbol is not defined, then the method is not executed Inside Main( ), both Trial( ) and Release( ) are called However, only TRIAL is defined Thus, Trial( ) is executed The call to Release( ) is ignored If you define RELEASE, then Release( ) will also be called If you remove the definition for TRIAL, then Trial( ) will not be called The Conditional attribute can also be applied to an attribute class (that is, a class that inherits Attribute) In this case, if the symbol is defined when the attribute is encountered during compilation, the attribute is applied Otherwise, it is not
Code 39 Creator In None
Using Barcode generator for Online Control to generate, create Code 39 Extended image in Online applications.
USS Code 128 Creation In None
Using Barcode encoder for Software Control to generate, create Code-128 image in Software applications.
17:
Recognizing Code39 In Visual C#
Using Barcode reader for Visual Studio .NET Control to read, scan read, scan image in .NET framework applications.
Data Matrix Drawer In Java
Using Barcode generator for Java Control to generate, create Data Matrix 2d barcode image in Java applications.
R u n t i m e Ty p e I D , R e f l e c t i o n , a n d A t t r i b u t e s
Conditional methods have a few restrictions First, they must return void Second, they must be members of a class or structure, not an interface Third, they cannot be preceded with the override keyword
PART I
The Obsolete Attribute
The Obsolete attribute, which is short for SystemObsoleteAttribute, lets you mark a program element as obsolete Here is one of its forms: [Obsolete( message )] Here, message is displayed when that program element is compiled Here is a short example:
// Demonstrate the Obsolete attribute using System; class Test { [Obsolete("Use MyMeth2, instead")] public static int MyMeth(int a, int b) { return a / b; } // Improved version of MyMeth public static int MyMeth2(int a, int b) { return b == 0 0 : a /b; } static void Main() { // Warning displayed for this ConsoleWriteLine("4 / 3 is " + TestMyMeth(4, 3)); // No warning here ConsoleWriteLine("4 / 3 is " + TestMyMeth2(4, 3)); } }
When the call to MyMeth( ) is encountered in Main( ) when this program is compiled, a warning will be generated that tells the user to use MyMeth2( ) instead A second form of Obsolete is shown here: [Obsolete( message , error)] Here, error is a Boolean value If it is true, then use of the obsolete item generates a compilation error rather than a warning The difference is, of course, that a program containing an error cannot be compiled into an executable program
This page intentionally left blank
CHAPTER
Generics
his chapter examines one of C# s most sophisticated and powerful features: generics Interestingly, although generics are now an indispensable part of C# programming, they were not included in the original 10 release Instead, they were added by C# 20 It is not an overstatement to say that the addition of generics fundamentally changed the character of C# Not only did it add a new syntactic element, it also added new capabilities and resulted in many changes and upgrades to the library Although it has been a few years since the inclusion of generics in C#, the effects still reverberate throughout the language The generics feature is so important because it enables the creation of classes, structures, interfaces, methods, and delegates that work in a type-safe manner with various kinds of data As you may know, many algorithms are logically the same no matter what type of data they are being applied to For example, the mechanism that supports a queue is the same whether the queue is storing items of type int, string, object, or a user-defined class Prior to generics, you might have created several different versions of the same algorithm to handle different types of data Through the use of generics, you can define a solution once, independently of any specific type of data, and then apply that solution to a wide variety of data types without any additional effort This chapter describes the syntax, theory, and use of generics It also shows how generics provide type safety for some previously difficult cases Once you have completed this chapter, you will want to examine 25, which covers Collections There you will find many examples of generics at work in the generic collection classes
Copyright © OnBarcode.com . All rights reserved.