C#Your visual blueprint for building .NET applications phần 5 pptx

int int Param1 ™ Type the indexer parameter name(s) in the Parameter name field. £ Add the name(s) to the Parameter list field by clicking the Add button. ¢ Click to select the indexer modifier from the Indexer modifiers area. ∞ Type a comment for your indexer. § Click the Finish button. ■ The indexer code skeleton appears in your class code so you can edit it. WORKING WITH TYPES AND INTERFACES 5 Properties and indexers have some similarities — the most obvious is that all of the rules defined for the properties get and set accessors also apply to the indexer get and set accessors. Although properties and indexers are related, you should be aware of some significant differences: • Visual C# identifies a property by its name and an indexer by its signature. • You can access a property with a simple name. You must access an indexer through an element. • A property can have a static object that does not change. An indexer must contain instance information generated by the class. • The get accessor of a property has no additional parameters. The get accessor of an indexer has the same parameters as the indexer. • The set accessor of a property contains the implicit value parameter. The set accessor of an indexer has the value parameter and the additional indexer parameters. 115 063601-X Ch05.F 10/18/01 11:59 AM Page 115 A method is a piece of code that implements an action that a class or object can perform. Methods appear within a class and provide additional information that classes cannot handle. C# supports two types of methods: static and non-static. All objects in a class can access the static methods in that class without creating any instance of that class. Instances of a class can only access non-static methods. For more information on adding static and non-static methods, see pages 6 to 13. You can overload methods, which means that different methods can have the same name as long as each separate method has a unique signature. C# identifies a signature by looking for specific method features including the method name and the method parameters. You can only add a method when you are editing a class. When you program a method you can do so in one of two ways: in code or by using the C# Method Wizard. The C# Method Wizard contains fields with basic method information that you can enter and choose from. Once you finish entering information into the wizard, the basic method code information appears in your code so you can edit it. VIEW INFORMATION ABOUT METHODS 116 VIEW INFORMATION ABOUT METHODS C# Index Crtl+Alt+F2 ⁄ Click Start ➪ Programs ➪ Microsoft Visual Studio .NET 7.0 ➪ Microsoft Visual Studio .NET 7.0. ■ The Start page appears. ¤ Click Help. ‹ Click Index. 073601-X Ch06.F 10/18/01 11:59 AM Page 116 When you add a new method, you can have several methods with the same name with different signatures in the same class. However, if you try to add a method and another class type such as an interface with the same name, the MDE window would register an error and the compiler would not be able to run the program. If you have the same name for the method and interface but the method and interface were in separate classes, then C# would have no problem. Though C# looks for the module name and the formal parameter list when determining a module signature, it does not look for the return type or the names of the parameters. So if you receive an error from the MDE window about signatures, check to see that your module names and lists are different for each module. PROGRAMMING METHODS AND EVENTS 6 117 adding in C# adding in C# methods, adding in ■ The Index window appears. › Type methods in the Look for field. ˇ Click the adding in C# entry in the Index list box. ■ The C# Add Method Wizard appears so you can learn about adding methods. 073601-X Ch06.F 10/18/01 12:00 PM Page 117 Visual C# Projects Console Application ⁄ Click Start ➪ Programs ➪ Microsoft Visual Studio .NET 7.0 ➪ Microsoft Visual Studio .NET 7.0. ■ The Start page appears. ¤ Click New Project. ■ The New Project window appears. ‹ Click the Console Application icon in the Templates pane. › Type a name for the file. ˇ Click OK. A s with a property and an indexer, C# gives you two ways to add a method. If you like the step-by-step functionality provided by a wizard, the C# Add Method Wizard lets you add a method automatically. You can also add a method in code. When you add a method in code you start with the method keyword. You can add information that precedes the keyword: whether the method is static or non-static (the default is non-static) and whether the method contains a void type. The void type renders the method invisible where it takes on no parameters and returns no values. After you enter the method keyword, you can enter the optional method declarations. These declarations include various attributes, method modifiers, the return type, and then the name of the method itself. Then you begin to add the information within your method. Attributes include names that you can enter in your class and refer to in your method. An attribute is a good way to identify information that you want to include in your class such as your company Web site. The method modifiers help determine the access to your method from your class and other code in your project. ADD A METHOD C# 118 ADD A METHOD 073601-X Ch06.F 10/18/01 12:00 PM Page 118 Add Method . . . Class View - M. . . Class1 Public Void int Add Method {}Method Á Click the Class View tab. ‡ Click the plus sign ( ) next to the Method name. ° Click the plus sign ( ) next to the {} Method name. · Right-click the class name to open the pop-up menu. ‚ Click Add ➪ Add Method. ■ The C# Method Wizard window appears. PROGRAMMING METHODS AND EVENTS 6 You use the return keyword in all methods except one: the void type. When you specify the void method type, you do not need to include the return keyword because the return type is automatically void. 119 TYPE THIS: using System; class VoidTest { public static void Main() { int diameter = 25; Console.WriteLine("The diameter is {0}", diameter); } } RESULT: The diameter is 25 CONTINUED 073601-X Ch06.F 10/18/01 12:00 PM Page 119 void int void Int Parameter1 int — Type the method name in the Method name field. Note: The Method signature field at the bottom reflects the changes to the method code as you type information into the wizard fields. ± Type the parameter name in the Parameter name field. ¡ Click Add. ■ The added parameter name appears in the Parameter list field. A fter you include the attributes and method access modifiers, you can further define your method using several different modifiers. If your method resides in an inheriting class and you also have a modifier in your base class, you can disregard the method in the base class by adding the new keyword. Using the new keyword in your method effectively hides the base class method so your class only pays attention to the method in its class. You can determine if the method will have the static, virtual, override, abstract, or extern status. A static method lets all objects in its class access it. You can use a virtual method in an inheriting class; a virtual method checks to see if any methods in any related class must override that method. An override method tells that method to override any methods in any related classes. The abstract method introduces a new virtual method but acts as a placeholder for a different method in a related class that will override the abstract method. The extern modifier lets you create an external method. Once you add the modifier you can determine the return type and then enter the name of the method. After you add the method name you can begin work on the body of your method. ADD A METHOD C# 120 ADD A METHOD (CONTINUED) 073601-X Ch06.F 10/18/01 12:00 PM Page 120 void int int Parameter1 ™ Click to select a method modifier from the Method modifiers check box area. £ Type a comment in the Comment field. ¢ Click Finish. ■ The method code appears in the parent window. PROGRAMMING METHODS AND EVENTS 6 C# lets you return multiple values from one method by using the out parameter. 121 TYPE THIS: using System; public class OutTest { public static int Output(out int a) { a = 25; return 0; } public static void Main() { int a; Console.WriteLine(Output(out a)); Console.WriteLine(a); } } RESULT: 0 25 073601-X Ch06.F 10/18/01 12:00 PM Page 121 Visual C# Projects Console Application ⁄ Click Start ➪ Programs ➪ Microsoft Visual Studio .NET 7.0 ➪ Microsoft Visual Studio .NET 7.0. ■ The Start page appears. ¤ Click New Project. ■ The New Project window appears. ‹ Click the Console Application icon in the Templates pane. › Type a name for the file. ˇ Click OK. A static method maintains its information regardless of how many class instances are created; you can use static methods for maintaining a value such as the boiling temperature of water. Like classes, methods are either static or instance members of the class. A static method contains information that will remain constant so the class can use it repeatedly. This is useful when you want to make calculations in your class with a value that is always constant. You must explicitly include the static option before typing in the method keyword in your code. If you do not, then C# will automatically consider the method to be non-static. This chapter discusses non-static methods in greater detail later on. If you declare a static modifier with your method, then you cannot also include a virtual, abstract, or override modifier. If you try to, the MDE window will point out the error and your project will not compile. The static modifier remains with that class and only with that class — it does not rely on any methods in any other inheriting or base class. Because virtual, abstract, and override modifiers deal with inheriting classes, they do not apply to static modifiers. You cannot access static members through object instances that occur when you run your project. That is what non- static methods are for. You can access static methods through both value and reference types. ADD STATIC METHODS C# 122 ADD STATIC METHODS 073601-X Ch06.F 10/18/01 12:00 PM Page 122 Add Method Add Class1 int void StaticMethod Á Click the Class View tab. ‡ Click the plus sign ( ) next to the Method name. ° Click the plus sign ( ) next to the {} Method name. · Right-click the class name. ‚ Click Add ➪ Add Method. ■ The C# Method Wizard appears. — Type the method name in the Method name field. Note: The Method signature field at the bottom reflects the changes to the method code as you type information into the wizard fields. PROGRAMMING METHODS AND EVENTS 6 If you need to return more than one variable from your static method, you can do so using the params keyword. 123 TYPE THIS: using System; public class Params { public static void Parameter(params int[] list) { for ( int x = 0 ; x < list.Length ; x++ ) Console.WriteLine(list[x]); Console.WriteLine(); } public static void Main() { Parameter(10, 15, 20); } } RESULT: 10 15 20 CONTINUED 073601-X Ch06.F 10/18/01 12:00 PM Page 123 void Class1.cs int ± Type the parameter name in the Parameter name field. ¡ Click Add. ■ The added parameter name appears in the Parameter list field. ™ Click to select a method modifier from the Method modifiers check box area. £ Click Finish. ■ The static method code appears in the parent window. ¢ Move the static method code above the Main method code. ∞ Type the Record class code that establishes variables and static methods for adding to the number of records. C # uses simple names for accessing many different elements in a C# project, and methods are no different. However, if you have a static method then how you program static methods and other static information in your method determines if you can use simple names or not. Simple names for a variable can be just one letter, such as x. When you declare variables and associate them with value types, the methods you include those declarations in determine whether your program can process those variables. For example, you can declare two variables of integers with the simple names a and b, with a declared as a non-static member and b declared as a static member. If you place the two variables in a non-static method and evaluate them later in your class, you will have no trouble with your evaluation. However, if you put those two variables in a static method you will only be able to evaluate the static variable b because a static method cannot access a non-static variable. If you decide to plunge ahead anyway and try to evaluate a non-static variable in a static method, you will find that the MDE window will protest that action and your program will not compile until you fix the problem. ADD STATIC METHODS C# 124 ADD STATIC METHODS (CONTINUED) 073601-X Ch06.F 10/18/01 12:00 PM Page 124 [...]... PM Page 1 25 PROGRAMMING METHODS AND EVENTS 6 You can reference a static method in what Visual Studio NET refers to as a member-access format The member-access format contains the full version of the type and its associated identifier The member-access format comes in the form of the type, a period, and then the identifier For example, you can have the member access type int.number C# and the Visual Studio... Console.WriteLine statement after the foreach statement so you can see all of the array elements when your program runs Another example is passing along integers from your array to a mathematical formula for further processing An array is a collections class that uses the System.Array base class You can use the foreach statement for both arrays and collections See page 150 for more information on implementing... events in Visual Studio NET such as mouse events Event handlers are used with Windows forms in C# because they are well-suited for the events, such as a button click and the methods that follow, such as a window opening These parameters help determine other information that is pertinent to a Windows form or any other graphical user interface that you want to program For example, you may need information... and the Visual Studio NET suite do not force you to use the member-access format because many of the access types have aliases that C# refers to If you reference your static method (or any other static member) in member-access form you must do so in the form E.M The E must stand for the type that your method uses, not the object The M stands for the type identifier For example, if your method is of the... four pages and read about delegates before you continue on PROGRAM EVENTS Visual C# Projects Console Applications ⁄ Click Start ➪ Programs ➪ Microsoft Visual Studio NET 7.0 ➪ Microsoft Visual Studio NET 7.0 I The Start page appears ¤ Click New Project 132 I The New Project window appears ‹ Click the Console Application icon in the Templates pane › Type a name for the file ˇ Click OK Á Type the code... Though the member-access E.M format is the same as with static methods, the E cannot represent a type Instead, the E must represent the class instance Usually the member-access format does not include the identifier signified by M because the instance expression signified by E is all the information needed Another reason for using the member-access format is that you can perform a member lookup A member... The event handler code contains two parameters for handling the event The sender parameter references the argument that sent the event The event object parameter sends an object specific to the handled event ADD AN EVENT HANDLING METHOD Visual C# Projects Form1.cs Console Applications ⁄ Click Start ➪ Programs ➪ Microsoft Visual Studio NET 7.0 ➪ Microsoft Visual Studio NET 7.0 I The Start page appears... the method that it is looking for has the same signature as the delegate ENTER DELEGATES Visual C# Projects Console Applications ⁄ Click Start ➪ Programs ➪ Microsoft Visual Studio NET 7.0 ➪ Microsoft Visual Studio NET 7.0 130 I The Start page appears ¤ Click New Project I The New Project window appears ‹ Click the Console Application icon in the Templates pane › Type a name for the file ˇ Click OK 073601-X... Programs ➪ Microsoft Visual Studio NET 7.0 ➪ Microsoft Visual Studio NET 7.0 144 I The Start page appears ¤ Click New Project I The New Project window appears ‹ Click the Console Application icon in the Templates pane › Type a name for the file ˇ Click OK 083601-X Ch07.F 10/18/01 12:00 PM Page 1 45 USING ARRAYS 7 You can also iterate through an array using the for statement if you want The for statement requires... even); } } Á Type the code that establishes the array ‡ Type the foreach argument that squares each of the elements in the array and outputs that information to the screen There are 5 odd numbers and 1 even number ° Run the program by · Save the program as the pressing the F5 key filename I The element square information appears on the screen 1 45 083601-X Ch07.F 10/18/01 12:00 PM Page 146 C# SORT ARRAYS . member access form is int.NumberOne. 1 25 073601-X Ch06.F 10/18/01 12:00 PM Page 1 25 Visual C# Projects Console Applications ⁄ Click Start ➪ Programs ➪ Microsoft Visual Studio .NET 7.0 ➪ Microsoft Visual. 10/18/01 12:00 PM Page 133 Visual C# Projects Form1.cs Console Applications ⁄ Click Start ➪ Programs ➪ Microsoft Visual Studio .NET 7.0 ➪ Microsoft Visual Studio .NET 7.0. ■ The Start page. Ch06.F 10/18/01 12:00 PM Page 131 Visual C# Projects Console Applications ⁄ Click Start ➪ Programs ➪ Microsoft Visual Studio .NET 7.0 ➪ Microsoft Visual Studio .NET 7.0. ■ The Start page appears. ¤