For Each Iteration Statements
2.13.3.3 For Each
The For Each statement is similar to the For statement, except that the loop variable need not be numeric, and successive iterations do not increment the loop variable. Instead, the loop variable takes successive values from a collection of values. Here is the syntax: For Each variable In expression statements Next [ variable ] The loop variable can be of any type. The expression must be a reference to an object that exposes the IEnumerable interface interfaces are discussed later in this chapter. Generally, types that are considered collections expose this interface. The .NET Framework class library provides several useful collection types, which are listed in Chapt er 3 . See Sect ion 2.5.4 earlier in this chapter for an explanation of what constitutes a collection type. The type of the items in the collection must be compatible with the type of the loop variable. The statements in the body of the loop execute once for each item in the collection. During each iteration, the loop variable is set equal to each consecutive item in the collection. Because all Visual Basic .NET arrays expose the IEnumerable interface, the For Each statement can be used to iterate through the elements of an array. For example: Dim a As Integer = {1, 2, 3, 4, 5} 60 Dim b As Integer For Each b In a Console.WriteLineb Next This is equivalent to the following code: Dim a As Integer = {1, 2, 3, 4, 5} Dim b As Integer Dim i As Integer For i = a.GetLowerBound0 To a.GetUpperBound0 b = ai Console.WriteLineb Next Because all arrays in Visual Basic .NET implicitly derive from the Array type in the System namespace, the a array in this example has access to methods defined on the Array type specifically GetLowerBound and GetUpperBound. In case youre interested, here is the equivalent code using a Do loop. This is essentially what the For Each statement is doing under the covers, although the For Each construct is likely to compile to faster code. Dim a As Integer = {1, 2, 3, 4, 5} Dim b As Integer Dim e As Object = a.GetEnumerator Do While CTypee.GetType .InvokeMemberMoveNext, _ Reflection.BindingFlags.InvokeMethod, Nothing, e, Nothing, Boolean b = CTypee.GetType .InvokeMemberCurrent, _ Reflection.BindingFlags.GetProperty, Nothing, e, Nothing, Integer Console.WriteLineb Loop2.13.4 Mathematical Functions
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» VB.NET - (O'Reilly) Programming Visual Basic NET
» What Is the Microsoft .NET Framework?
» hello, world An Example Visual Basic .NET Program
» Hello, Windows An Example Visual Basic .NET Program
» Hello, Browser An Example Visual Basic .NET Program
» Source Files Identifiers The Visual Basic .NET Language
» Numeric Literals String Literals Character Literals
» Date Literals Boolean Literals Nothing Summary of Literal Formats
» Custom Types Collections Types
» The Namespace Statement The Imports Statement
» Symbolic Constants Scope The Visual Basic .NET Language
» Access Modifiers Assignment The Visual Basic .NET Language
» Unary Operators Arithmetic Operators
» Relational Operators Operators and Expressions
» String-Concatenation Operators Bitwise Operators
» Logical Operators Operator Precedence
» Call Exit Branching Statements
» Goto If RaiseEvent Branching Statements
» Return Select Case Branching Statements
» For Each Iteration Statements
» Object Instantiation and New Constructors
» Handling Events Inheritance Classes
» Passing arrays as parameters
» Variable-length parameter lists Main method
» Implementing interface methods Overriding inherited methods
» Overloading Overloading inherited methods
» The MyBase Keyword Nested Classes Destructors
» Interfaces The Visual Basic .NET Language
» Enumerations The Visual Basic .NET Language
» Exceptions The Visual Basic .NET Language
» Delegates The Visual Basic .NET Language
» Using Events and Delegates Together
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» Summary The Visual Basic .NET Language
» Common Language Infrastructure CLI and Common Language Runtime CLR
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» A Brief Tour of the .NET Framework Namespaces
» Configuration File Format Configuration
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» Adding event handlers Creating a Form in Code
» Handling Form Events Windows Forms I: Developing Desktop Applications
» Relationships Between Forms Windows Forms I: Developing Desktop Applications
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» Component Attributes Windows Forms I: Developing Desktop Applications
» The Graphics Class 2-D Graphics Programming with GDI+
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» The Brush Class 2-D Graphics Programming with GDI+
» System colors The Color Structure
» Alpha Blending 2-D Graphics Programming with GDI+
» Antialiasing 2-D Graphics Programming with GDI+
» The PrintPageEventArgs Class Printing
» The OnBeginPrint and OnEndPrint Methods Choosing a Printer
» The PageSettings Class Printing
» The PrinterSettings Class Printing
» Page Setup Dialog Box Print Preview
» Summary Windows Forms I: Developing Desktop Applications
» The Button Class The CheckBox Class The ComboBox Class
» The DateTimePicker Class The GroupBox Class The ImageList Class
» The Label Class The LinkLabel Class
» The ListBox Class Common Controls and Components
» The ListBox.ObjectCollection Class
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» The TextBox Class The Timer Class
» Other Controls and Components
» Control Events Windows Forms II: Controls, Common Dialog Boxes, and Menus
» The Anchor Property Form and Control Layout
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» ColorDialog FontDialog OpenFileDialog Common Dialog Boxes
» PageSetupDialog PrintDialog PrintPreviewDialog SaveFileDialog
» Adding Menus in the Visual Studio .NET Windows Forms Designer
» Programmatically Creating Menus Menus
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» Summary Windows Forms II: Controls, Common Dialog Boxes, and Menus
» Setting control properties using attributes Adding event handlers
» AutoEventWireup Handling Page Events
» The Button control Web Controls
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» Other web controls Web Controls
» HTML Controls Handling Control Events
» Programmatically Instantiating Controls More About Server Controls
» More About Validation-Control Tag Attributes
» Using Validation-Control Properties Providing a Summary View of Validation Failures
» Performing Custom Validation Adding Validation
» Using Directives to Modify Web Page Compilation
» The Server Object ASP.NET Objects: Interacting with the Framework
» The Application Object The Session Object The Cache Object The Request Object
» The Response Object ASP.NET Objects: Interacting with the Framework
» Discovering Browser Capabilities ASP.NET and Web Forms: Developing Browser-Based Applications
» The Session Object Maintaining State
» The Application Object Maintaining State
» Session and Application Startup and Shutdown global.asax Compiles to a Class
» Adding Global Objects Application-Level Code and global.asax
» ASP.NET authorization Authorization
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» IUSR_ComputerName Impersonation Accessing Network Resources
» User Controls Designing Custom Controls
» Creating a custom server control using Visual Studio .NET
» Creating a custom server control in code Using a custom server control in Visual Studio .NET
» Summary ASP.NET and Web Forms: Developing Browser-Based Applications
» The WebService Attribute The WebMethod Attribute
» Testing a Web Service with a Browser
» Consuming a Web Service in Visual Studio .NET
» Consuming a Web Service in Notepad
» Synchronous Versus Asynchronous Calls
» Web-Service Descriptions Web-Service Discovery
» Limitations of Web Services Summary
» A Brief History of Universal Data Access Managed Providers
» Connecting to a SQL Server Database
» Connecting to an OLE DB Data Source
» The DataSet Class Finding Tables
» Finding Column Values Finding Column Definitions Changing, Adding, and Deleting Rows
» Writing Updates Back to the Data Source
» Relations Between DataTables in a DataSet
» The DataSets XML Capabilities
» Binding a DataSet to a Windows Forms DataGrid
» Binding a DataSet to a Web Forms DataGrid
» Typed DataSets ADO.NET: Developing Database Applications
» Reading Data Using a DataReader
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