VBScript Reference Manual for InduSoft Web Studio - ICP DAS

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VBScript Reference ManualInduSoft Web StudioProcedure StatementsThere are two types of procedure statements; the Sub procedure and the Function procedure. Both ofthese procedure statements are intended to encapsulate a set of statements that provide functionalitythat can be repeatedly called, but the difference between the two is how arguments are passed andresults returned.The Sub procedure is a series of VBScript statements (enclosed by Sub and End Sub statements) thatperform actions but don't return a value as part of the Sub name. A Sub procedure can take arguments(constants, variables, or expressions that are passed by a calling procedure). A resultant value or set ofvalues can be returned through the arguments. If a Sub procedure has no arguments, its Substatement must include an empty set of parentheses ().The Function procedure is a series of VBScript statements enclosed by the Function and EndFunction statements. A Function procedure is similar to a Sub procedure, but can also return a valuein the Function name. A Function procedure can take arguments (constants, variables, or expressionsthat are passed to it by a calling procedure). If a Function procedure has no arguments, its Functionstatement must include an empty set of parentheses. A Function returns a value by assigning a valueto its name in one or more statements of the procedure. The return type of a Function is always aVariant.Procedure StatementsFunction DescriptionCallTransfers control to a Sub or Function procedureEnd Function Immediately exits a Function procedureEnd Sub Immediately exits a Sub procedureExit Function Exit a Function, generally as a result of a conditionExit Sub Exit a Subroutine, generally as a result of a conditionFunction Declares the name, arguments, and code that form the body of a Function procedureGetRefAssociates an event handler with a specific functionSubDeclares the name, arguments, and code that form the body of a Sub procedure(Subroutine).20 InduSoft, Ltd.
InduSoft Web StudioVBScript Reference ManualObjects and ClassesTraditional programming is made up of a collection of subroutines and functions that are typicallyprocessed in a sequential or looping manner. In contrast, object oriented programming is a differentprogramming methodology where a program is viewed as being composed of a collection of individualobjects. These objects process data and can interact with other objects directly without having to beexplicitly programmed to do so. The advantages claimed by object-oriented program include codereusability, rapid deployment of large-scale complex tasks, and ease of use/debugging. Today, objectorientedprogramming is widely used and is supported with both programming languages (e.g. VB.NET,C++, Visual C++) and operating systems (e.g. Microsoft’s .NET architecture). Object-orientedprogramming has also become popular within scripting languages, such as VBScript. Beginning withVBScript 5.0, developers have been able to use user-defined Classes.The key concepts with object-oriented programming include:• ClassThe class is the highest level that defines a unit (set) of data and its behavior. Classes form thebasis for modularity and structure in an object-oriented program. The class should sufficientlydescribe the set of data, and the code for a class should be contained within it and be selfsufficient(except for operating system support). While the terms classes and objects often getused interchangeably, classes describe the structure of objects. One way to think of a class isthat it is a container for code. It can also be viewed as a template for an object. When a class isdeclared (instantiated) by the Set statement, it then becomes an object and memory is allocatedfor it.• ObjectAn object is an in-memory instance of a class. In computer science terms, it is a run-timemanifestation (instantiation) of a particular exemplar of a class. Each object has its own data,but the code within a class can be shared (for efficiency). Programs generally have multipleobjects. Multiple copies (objects) of a given class can be created. Objects are temporary, i.e.they can be created and removed at will, depending on the programming needs.• EncapsulationEncapsulation wraps the data and functions into a single unit, ensuring that the object can bechanged only through established interfaces. Encapsulation is sometimes referred to asinformation hiding. Some of these common interfaces are:o FieldsFields are simply public variables stored within the object, as defined by the class. Thesevariables store items of information about an object.oooPropertiesProperties, like fields, also store items of information on an object. But Properties useProperty procedures to control how values are set or returned. VBScript has two primaryProperty procedures; Let and Get. The Get property procedure retrieves a Propertyvalue, while the Let Property procedure assigns a value to the property value. A thirdProperty procedure Set is used with an Object inside of the Class block.MethodsMethods are a collection of subroutines (Sub) and function procedures (Function)declared within a class.EventsAn event is a message sent by an object announcing that something important hashappened.InduSoft, Ltd. 21
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