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There are several related classes whose collective purpose is to provide reusable, read-only, viewing, scrolling, searching, and printing capability for files, including variable length files. Although these classes are primarily designed for ASCII text and they anticipate using the Clarion ASCII Driver to access the files, they also work with binary files and with other database drivers. These classes can be used to build other components and functionality as well.

The classes that provide this read-only functionality are the ASCII Viewer classes. The ASCII Viewer classes and their respective roles are:

|  | ASCIIViewerClass | Supervisor class |
|  | ASCIIFileClass | Open, read, filter, and index the file |
|  | ASCIIPrintClass | Print one or more lines |
|  | ASCIISearchClass | Locate and scroll to text |

These classes are fully documented in the remainder of this chapter.

**ASCIIViewerClass**

The ASCIIViewerClass uses the ASCIIFileClass, the ASCIIPrintClass, and the ASCIISearchClass to create a single full featured ASCII file viewer object. This object uses a LIST control to display, scroll, search, and print the contents of the file. Typically, you instantiate only the ASCIIViewerClass in your program which, in turn, instantiates the other classes as needed.

**ASCIIFileClass**

The ASCIIFileClass identifies, opens (read-only), indexes, and page-loads a file's contents into a QUEUE. The indexing function speeds any reaccess of records and supports page-loading, which in turn allows browsing of very large files.

**ASCIIPrintClass**

The ASCIIPrintClass lets the end user specify a range of lines to print, then prints them. It also provides access to the standard Windows Print Setup dialog.

**ASCIISearchClass**

The ASCIISearchClass lets the end user specify a search value, case sensitivity, and a search direction, then scrolls to the next instance of the search value within the file.

**ASCIIViewerClass Relationship to Other Application Builder Classes**

The ASCIIViewerClass is derived from the ASCIIFileClass, plus it relies on the ASCIIPrintClass, ASCIISearchClass, ErrorClass, and PopupClass to accomplish some user interface tasks. Therefore, if your program instantiates the ASCIIViewerClass, it must also instantiate these other classes. Much of this is automatic when you INCLUDE the ASCIIViewerClass header (ABASCII.INC) in your program's data section. See the //Conceptual Example//.

**ASCIIViewerClass ABC Template Implementation**

The ABC Templates declare a local ASCIIViewer class //and //object for each instance of the ASCIIViewControl template. The ABC Templates automatically include all the classes necessary to support the functionality specified in the ASCIIViewControl template.

The templates //derive //a class from the ASCIIViewerClass for //each //ASCIIViewerClass in the application. The derived class is called //procedure//:Viewer# where //procedure// is the procedure name and # is the instance number of the ASCIIViewControl template. The templates provide the derived class so you can use the ASCIIViewControl template **Classes **tab to easily modify the viewer's behavior on an instance-by-instance basis.

The object is named Viewer# where # is the instance number of the control template. The derived ASCIIViewerClass is local to the procedure, is specific to a single ASCIIViewerClass and relies on the global ErrorClass object.

**ASCIIViewerClass Source Files**

The ASCIIViewerClass source code is installed by default to the Clarion \LIBSRC folder. The specific ASCIIViewerClass source code and their respective components are contained in:

| ABASCII.INC | ASCIIViewerClass declarations |
| ABASCII.CLW | ASCIIViewerClass method definitions |

**ASCIIViewerClass Conceptual Example**

The following example shows a typical sequence of statements to declare, instantiate, initialize, use, and terminate an ASCIIViewerClass object and related objects.

This example lets the end user select a file, then browse, scroll, search, and print from it.

** PROGRAM**

** MAP**

** END**

** INCLUDE('ABASCII.INC')                !declare ASCIIViewer Class**

**ViewWindow WINDOW('View a text file'),AT(3,7,296,136),SYSTEM,GRAY**

**       LIST,AT(5,5,285,110),USE(?AsciiBox),IMM**

**       BUTTON('&Print'),AT(5,120),USE(?Print)**

**       BUTTON('&Search'),AT(45,120),USE(?Search)**

**       BUTTON('&Close'),AT(255,120),USE(?Close)**

**      END**

**GlobalErrors ErrorClass                !declare GlobalErrors object**

**Viewer AsciiViewerClass,THREAD         !declare Viewer object**

**ViewerActive BYTE(False),THREAD        !Viewer initialized flag**

**Filename   STRING(255),THREAD          !FileName variable**

**StartSearch  LONG                      !hold selected line number**

**AsciiFile   FILE,DRIVER('ASCII'),NAME(Filename),PRE(A1),THREAD**

**RECORD     RECORD,PRE()**

**Line       STRING(255)**

**        END**

**       END**

** CODE**

** GlobalErrors.Init                   !initialize GlobalErrors object**

** OPEN(ViewWindow)                    !open the window**

**                                     !Initialize Viewer with: **

** ViewerActive=Viewer.Init( AsciiFile,| ! file label,**

**              A1:line,               | ! file field to display**

**              Filename,              | ! variable file NAME attribute**

**              ?AsciiBox,             | ! LIST control number**

**              GlobalErrors,          | ! ErrorClass object**

**              EnableSearch+EnablePrint)! features to implement flag**

** IF ~ViewerActive THEN RETURN.         ! if init unsuccessful, don't**

**                                       ! call other Viewer methods**