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The ViewManager class manages a VIEW. The ViewManager gives you easy, reliable access to all the sophisticated power and speed of VIEWs, through its proven objects. So you get this speed and power without reinventing any wheels.

**ViewManager Concepts**

The management provided by the ViewManager includes defining and applying multiple sort orders, range limits (key based filters), and filters (non-key based) to the VIEW result set. It also includes opening, buffering, reading, and closing the VIEW. Finally, it includes priming and validating the view's primary file record buffer in anticipation of adding or updating records.

All these services provided by the ViewManager are applied to a VIEW--not a FILE. A VIEW may encompass some or all of the fields in one or more related FILEs. The VIEW concept is extremely powerful and perhaps essential in a client-server environment with normalized data. The VIEW lets you access data from several different FILEs as though from a single file, and it does so very efficiently. See [[view  declare a  virtual  file .htm|VIEW]] in the //Language Reference //for more information.

In addition, the ViewManager supports buffering (some file drivers do not support buffering) which allows the performance of "browse" type procedures to be virtually instantaneous when displaying pages of records already read. Buffering (see [[buffer  set record paging .htm|BUFFER]]// //in the //Language Reference//) can also optimize performance when the file driver is a Client/Server back-end database engine (usually SQL-based), since the file driver can then optimize the calls made to the back-end database for minimum network traffic.

**ViewManager Relationship to Other Application Builder Classes**

The ViewManager relies on the FieldPairsClass and the RelationManager to do much of its work. Therefore, if your program instantiates the ViewManager it must also instantiate these other classes. Much of this is automatic when you INCLUDE the ViewManager header (ABFILE.INC) in your program's data section. See [[fieldpairsclass.htm|Field Pairs Classes]]// //and [[relationmanager.htm|Relation Manager Class]] for more information. Also, see the [[viewmanager overview.htm#b59zsq|Conceptual Example.]]

Perhaps more significantly, the ViewManager serves as the foundation of the BrowseClass and the ProcessClass. That is, both the BrowseClass and the ProcessClass are derived from the ViewManager.

**BrowseClass--An Interactive VIEW**

The BrowseClass implements an interactive VIEW that includes a visual display of records with scrolling, sorting, searching, and updating capabilities. See [[browseclass.htm|Browse Classes]] for more information.

**ProcessClass--A Non-Interactive VIEW**

The ProcessClass implements a batch (non-interactive) VIEW with sorting and updating capability, but no visual display and therefore no scrolling or searching capability. See [[processclass.htm|Process Class]] for more information.

**ViewManager ABC Template Implementation**

The ViewManager serves as the foundation to the Browse procedure template, the Report procedure template, and the Process procedure template, because all these templates rely on VIEWs.

The BrowseClass and the ProcessClass are derived from the ViewManager, and the ABC Templates instantiate these derived classes; that is, the templates do not instantiate the ViewManager independently of the BrowseClass or ProcessClass. The Browse procedure template instantiates the BrowseClass, and the Process and Report procedure templates instantiate the ProcessClass.

**ViewManager Source Files**

The ViewManager source code is installed by default to ..\LIBSRC. The specific ViewManager files and their respective components are:

|  | ABFILE.INC | ViewManager declarations |
|  | ABFILE.CLW | ViewManager method definitions |

**ViewManager Conceptual Example**

The following example shows a typical sequence of statements to declare, instantiate, initialize, use, and terminate a ViewManager object. This example simply establishes a VIEW with a particular sort order, range limit and filter, then processes the result set that fits the range and filter criteria.

** PROGRAM**

**    INCLUDE('ABFILE.INC')             !declare ViewManager class**

**    MAP                               !program map**

**    END**

**GlobalErrors  ErrorClass              !declare GlobalErrors object**

**View:Customer  ViewManager            !declare View:Customer object**

**Access:CUSTOMER CLASS(FileManager)    !declare Access:Customer object**

**Init             PROCEDURE**

**                END**

**Relate:CUSTOMER CLASS(RelationManager)!declare Relate:Customer object**

**Init             PROCEDURE**

**                END**

**CUSTOMER FILE,DRIVER('TOPSPEED'),PRE(CUS),THREAD,BINDABLE**

**BYNUMBER  KEY(CUS:CUSTNO),NOCASE,OPT,PRIMARY**

**Record    RECORD,PRE()**

**CUSTNO     LONG**

**NAME       STRING(30)**

**ZIP        DECIMAL(5)**

**          END**

**        END**

**Customer:View  VIEW(CUSTOMER)    !declare Customer VIEW**

**               END**

**Low          LONG                !low end of range limit**

**High         LONG(1000)          !high end of range limit**

**ProgressMsg  STRING(60)**

**ProgressWindow WINDOW('Processing...'),AT(,,215,60),GRAY,TIMER(100)**

**          STRING(@S60),AT(1,21,210,10),USE(ProgressMsg),CENTER**

**          BUTTON('Cancel'),AT(87,37,45,14),USE(?Cancel)**

**               END**

** CODE**

** GlobalErrors.Init                          !initialize GlobalErrors object**

** Relate:CUSTOMER.Init                       !initialize Relate:Customer object**

** View:Customer.Init(Customer:View,Relate:CUSTOMER) !initialize View:Customer object**

** View:Customer.AddSortOrder( CUS:BYNUMBER ) !add sort BYNUMBER**

** View:Customer.AppendOrder( 'CUS:Name,CUS:ZIP' )  !add secondary sorts**

** View:Customer.AddRange(CUS:CUSTNO,Low,High)!add a range limit**

** View:Customer.SetFilter( 'CUS:ZIP=33066','1')   !add filter #1**

** Relate:CUSTOMER.Open                       !open customer &amp; related files**

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

** ProgressMsg='Processing...'**

** ACCEPT**

**  CASE EVENT()**

**  OF Event:OpenWindow**

**   View:Customer.Reset(1)            !open view, apply range &amp; filter**

**  OF Event:Timer**

**   CASE View:Customer.Next()         !get next view record**

**   OF Level:Notify                   !if end of file, stop**

**    POST(EVENT:CloseWindow)**

**    BREAK**

**   OF Level:Fatal                    !if fatal error, stop**

**    POST(EVENT:CloseWindow)**

**    BREAK**

**   END**

**   CUS:ZIP=33065                     !process the record**

**   IF Relate:CUSTOMER.Update()       !update customer &amp; related files**

**    BREAK**

**   ELSE**

**    ProgressMsg = CLIP(CUS:Name)&amp;' zip changed to '&amp;CUS:ZIP**

**    DISPLAY(ProgressMsg)**

**   END**

**  END**

**  IF FIELD() = ?Cancel               !if user cancelled, stop**

**   IF EVENT() = Event:Accepted**

**    POST(Event:CloseWindow)**

**   END**

**  END**

** END**

** Relate:CUSTOMER.Close               !close customer &amp; related files**

** View:CUSTOMER.Kill                  !shut down View:Customer object**

** Relate:CUSTOMER.Kill                !shut down Relate:Customer object**

** GlobalErrors.Kill                   !shut down GlobalErrors object**

**Access:CUSTOMER.Init PROCEDURE**

** CODE**

** PARENT.Init(Customer,GlobalErrors)**

** SELF.FileNameValue = 'CUSTOMER.TPS'**

** SELF.Buffer &amp;= CUS:Record**

** SELF.AddKey(CUS:BYNUMBER,'CUS:BYNUMBER',1)**

** SELF.LazyOpen = False**

**Relate:CUSTOMER.Init PROCEDURE**

** CODE**

** Access:CUSTOMER.Init**

** PARENT.Init(Access:CUSTOMER,1)**