Chapter 1 INTRODUCTION SYS-ED/ COMPUTER EDUCATION TECHNIQUES, INC.

Transcription

1 hapter 1 INTRODUTION SYS-ED/ OMPUTER EDUATION TEHNIQUES, IN.

2 Objectives You will learn: Theory and terminology of OOPS. Objects, properties, and methods. How to record and read a macro. How to edit a recorded macro. How to execute a macro. SYS-ED \OMPUTER EDUATION TEHNIQUES, IN. (VBA - 0.7) h 1: Page i

3 Objects are the fundamental building blocks of Visual Basic. 1 Objects, Properties, and Methods Every element of MS Office, documents, tables, paragraphs, bookmarks, fields, are Visual Basic objects. 1.1 Objects and ollections An object represents an element of MS Office, such as a document in MS Word, a cell in a MS Excel document, a field in a MS Access table or a single character in any kind of document. A collection is an object that contains several other objects, usually of the same type. Example: All the bookmark objects in a document are contained in a single collection object. Using properties and methods, a single object or an entire collection of objects can be modified. SYS-ED \OMPUTER EDUATION TEHNIQUES, IN. (VBA - 0.7) h 1: Page 1

4 1.2 Property A property is an attribute of an object or an aspect of its behavior. Properties of a document include its name, its content, and its save status, as well as whether change tracking is turned on. To change the characteristics of an object, the values of its properties must be changed. To set the value of a property, follow the reference to an object with a period, the property name, an equal sign, and the new property value. Example: This code turns on change tracking in the document named "MyDoc.doc." Documents("MyDoc.doc").TrackRevisions = True Documents refers to the collection of open documents, and the name "MyDoc.doc" identifies a single document in the collection. The TrackRevisions property is set for that single document. Some properties cannot be set. The Help topic for a property indicates whether that property can be set/changed (read-write) or can only be read (read-only). Information about an object can be ascertained by returning the value of one of its properties. Example: The code returns the name of the active document. docname = ActiveDocument.Name ActiveDocument refers to the document in the active window in Word. The name of that document is assigned to the variable docname. The Object Browser in the Visual Basic Editor also displays the read-write status at the bottom of the browser window when the property is selected. SYS-ED \OMPUTER EDUATION TEHNIQUES, IN. (VBA - 0.7) h 1: Page 2

5 1.3 Methods A method is an action that an object can perform. Methods often have arguments that qualify how the action is performed. Example: This code prints the first three pages of the active document. ActiveDocument.PrintOut From:=1, To:=3 In most cases, methods are actions and properties are qualities. Using a method causes something to happen to an object, while using a property returns information about the object or it causes a quality about the object to change. 1.4 Returning an Object Most objects are returned by returning a single object from the collection. For example, the Documents collection contains the open Word documents. The Documents property of the Application object, which is the object at the top of the Word object hierarchy, is used to return the Documents collection. After the collection has been accessed, a single object can be returned by using an index value in parentheses. The index value is usually a number or a name. Example: Documents(1).lose This code uses the Documents property to access the Document collection. The index number is used to return the first document in the Documents collection. The lose method is then applied to the Document object to close the first document in the Documents collection. SYS-ED \OMPUTER EDUATION TEHNIQUES, IN. (VBA - 0.7) h 1: Page 3

6 2 Recording a Macro to Generate ode In Word, Excel or PowerPoint, if the situation arises where the programmer is unsure of which Visual Basic method or property to use, the macro recorder can be turned on and the action can be performed manually. The macro recorder translates the actions into Visual Basic code. After the actions are recorded, the code can be modified. In MS Word, to ascertain what property or method to use to indent a paragraph: 1. On the Tools menu, point to Macro, and then click Record New Macro. 2. hange the default macro name if you'd like and click OK to start the recorder. 3. On the Format menu, choose Paragraph. 4. hange the left paragraph indent value and click OK. 5. lick the Stop Recording button on the Stop Recording toolbar. 6. On the Tools menu, point to Macro, and then click Macros. 7. Select the macro name from Step 2 and click the Edit button. 8. View the Visual Basic code to determine the property that corresponds to the left paragraph indent (the LeftIndent property). 9. Position the insertion point within LeftIndent and press F1 or click the Help button. Within the topic, examples can be viewed and it is possible to review the objects that support the LeftIndent property (click Applies To). Recorded macros use the Selection property to return the Selection object. Example: This instruction indents the selected paragraphs by a half inch. Selection.ParagraphFormat.LeftIndent = InchesToPoints(0.5) A recorded macro can be modified to work with Range objects. SYS-ED \OMPUTER EDUATION TEHNIQUES, IN. (VBA - 0.7) h 1: Page 4

7 2.1 Revising Recorded Visual Basic Macros The macro recorder is a good for exploring the Visual Basic methods and properties and to create very simple modules. If a programmer doesn't know what properties or methods to use, the macro recorder can be turned on and then manually perform the action. The macro recorder translates the actions into Visual Basic code. There are, however, some limitations to recording macros. The following items cannot be recorded: onditional branches. Variable assignments. Looping structures. ustom user forms. Error handling. Text selections made with the mouse; keyboard combinations must be used. A macro can be enhanced by revising the code recorded into a module. SYS-ED \OMPUTER EDUATION TEHNIQUES, IN. (VBA - 0.7) h 1: Page 5

8 2.2 Removing Unnecessary odes When recording a macro that involves selecting an option in a dialog box, the macro recorder records the settings of all the options in the dialog box. This occurs even if only one or two options are changed. This recorded macro includes a number of options from the Paragraph dialog box (Format menu) Sub Macro1() With Selection.ParagraphFormat.LeftIndent = InchesToPoints(0).RightIndent = InchesToPoints(0).SpaceBefore = 6.SpaceAfter = 6.LineSpacingRule = 0.Alignment = wdalignparagraphleft.widowontrol = True.KeepWithNext = False.KeepTogether = False.PageBreakBefore = False.NoLineNumber = False.Hyphenation = True.FirstLineIndent = InchesToPoints(0).OutlineLevel = 10 End With End Sub If it is necessary to change only the spacing before and after the paragraph, the macro can be changed to the following: Sub MyMacro() With Selection.ParagraphFormat.SpaceBefore = 6.SpaceAfter = 6 End With End Sub The simplified macro executes faster because it sets fewer properties. Only the spacing before and after are changed; all the other settings for the selected paragraphs are unchanged. Also, this guards the macro against undesired changes. SYS-ED \OMPUTER EDUATION TEHNIQUES, IN. (VBA - 0.7) h 1: Page 6

9 2.3 Removing Unnecessary Arguments When the macro recorder records a method, the values of all the arguments are included. The following macro was recorded when the document named Test.doc was opened. The resulting macro includes all the arguments for the Open method Sub Macro1() Documents.Open FileName:=":\My Documents\Test.doc", onfirmonversions:= _ False, ReadOnly:=False, AddToRecentFiles:=False, PasswordDocument:="", _ PasswordTemplate:="", Revert:=False, WritePasswordDocument:="", _ WritePasswordTemplate:="", Format:=wdOpenFormatAuto End Sub The arguments that are not needed can be removed from the recorded macro. It is possible to remove all of arguments set to an empty string by setting WritePasswordDocument:="") Sub MyMacro() Documents.Open FileName:=":\My Documents\Test.doc", onfirmonversions:= _ False, ReadOnly:=False, AddToRecentFiles:=False, _ Revert:=False, Format:=wdOpenFormatAuto End Sub SYS-ED \OMPUTER EDUATION TEHNIQUES, IN. (VBA - 0.7) h 1: Page 7

10 3 MS Access Macros and Modules In Microsoft Access, many tasks can be accomplished with macros or through the user interface. Whether to use a macro or Visual Basic for Applications often depends on the particular task. 3.1 Macros Macros are an easy way to take care of simple details such as opening and closing forms, showing and hiding toolbars, and running reports. The database objects can be tied together very easily, because there's little syntax to remember; the arguments for each action are displayed in the lower part of the Macro window. In addition to the ease of use macros provide, you must use macros certain tasks. SYS-ED \OMPUTER EDUATION TEHNIQUES, IN. (VBA - 0.7) h 1: Page 8

11 3.2 Using Visual Basic You should use Visual Basic instead of macros if you want to: Make your database easier to maintain. Because macros are separate objects from the forms and reports that use them, a database containing many macros that respond to events on forms and reports can be difficult to maintain. In contrast, Visual Basic event procedures are built into the form's or report's definition. If you move a form or report from one database to another, the event procedures built into the form or report move with it. reate your own functions. Microsoft Access includes many built-in functions, such as the IPmt function, which calculates an interest payment. These functions can be used to perform calculations without having to create complicated expressions. Using Visual Basic, it is possible to create user defined functions either to perform calculations that exceed the capability of an expression or to replace complex expressions. Mask error messages. When something unexpected happens while a user is working with your database, and Microsoft Access displays an error message, the message can be quite mysterious to the user, especially if the user isn't familiar with Microsoft Access. Using Visual Basic, the error can be detected when it occurs and either a user friendly message can be displayed or some action can be taken. reate or manipulate objects. In some situations, instead of creating or modifying an object in that object's Design view, one you may want to manipulate the definition of an object in code. Using Visual Basic, all the objects in a database, as well as the database itself can be manipulated. Perform system-level actions. Using Visual Basic the following tasks can be performed: heck to see if a file exists on the system. Use Automation or dynamic data exchange (DDE) to communicate with other Windows-based applications such as Microsoft Excel all functions in Windows dynamic-link libraries (DLLs). SYS-ED \OMPUTER EDUATION TEHNIQUES, IN. (VBA - 0.7) h 1: Page 9

12 Manipulate records one at a time. Visual Basic allows stepping through a set of records one record at a time and performing an operation on each record. In contrast, macros work with entire sets of records at once. Pass arguments to Visual Basic procedures. With Visual Basic arguments can be passed to the code at the time it is run or variables can be used for arguments. This gives a great deal of flexibility in how Visual Basic procedures run. SYS-ED \OMPUTER EDUATION TEHNIQUES, IN. (VBA - 0.7) h 1: Page 10