Advanced Interactive Programming Componentbased Programming cont' Componentbased Database Programmin

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Advanced Interactive ProgrammingComponent-based
Programming (cont.) Component-based Database
Programming
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Outline

• ActiveX code components
• Create code components in VB
• ADO (ActiveX Data Object) data controls
• Data-aware controls
• Data manipulation in VB

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ActiveX Code Components

• Similar to libraries of objects
• ActiveX code components are characterized by
  their location relative to their clients. A
  client refers to an application that uses a
  components code by creating objects and calling
  their properties and methods
• Two types
• ActiveX DLL - in-process components
• ActiveX EXE - out-of-process components

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ActiveX DLL In-Process Components

• The fastest way of accessing objects without
  marshalling across process boundaries.
• Not executable by itself
• Used by others
• Usually no GUI

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ActiveX DLL

• These DLLs adhere to the Component Object Model,
  i.e. COM, which defines a set of protocols about
  how components interact with each other
• DLLs announce their presence in the Windows
  Registry
• They reside in the operating system area rather
  than with applications
• They are called when needed --- a dynamic link -
  this gives rise to the term Dynamic Link Library
  or DLL

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ActiveX DLL Example SpellChecker

• Create an ActiveX DLL component that uses
  Microsoft Words spell checker to check the
  spelling of any string
• Create a standard exe application to test the DLL
• The GUI of the testing application is shown below
• Function input a word, the program check if the
  word is spelled correctly and show the
  information in the label

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Step1 Start an ActiveX DLL Project
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Files in DLL Project

• Could contain Forms, standard modules and class
  module
• By default, at least one class module but could
  contain more class modules
• Design the interface that is, the properties,
  methods, and events for each class provided by
  your component

Name the project members
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Step2 Code Programming
Functions must be declared as public so that they
can be called by applications
Create a reference
Assign the reference an object
Call the method in the object
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Step3 Publishing the DLL

• Describe the DLL appropriately via project
  property
• Compile the project into .dll file and register
  it in the Windows Registry

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Testing ActiveX DLL Components

• Could be done using a separate standard exe
  application
• Could use groups to facilitate testing DLLs
• This bypasses the need to open and close separate
  projects while debugging a DLL with a client
  application
• Make reference to the DLL in the client
  application
• Declare one or more DLL class instances in client

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Step4 Design the Testing Application

• GUI design

Create a form that uses the DLL
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Step4 Design the Testing Application

• Code programming

Create a reference to the DLL
Assign an object to the reference
Call the public method of the DLL
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DLL References and Object Browser

• Use the References of the Project menu to make
  references to the necessary DLL type libraries
• You can declare objects for any type that are
  defined within the type library

Reference to the DLL
View DLL interfaces
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ActiveX DLL Creation Summary

• Determine the features your component will
  provide.
• Determine what class modules are required to
  divide the functionality of the component in a
  logical fashion.
• Create a ActiveX DLL project and design any forms
  your component will display.
• Design the interface that is, the properties,
  methods, and events for each class provided by
  your component.

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ActiveX DLL Creation Summary

• Implement the forms required by your component.
• Implement the interface of each class.
• Create a project group consisting of your
  component project and a test project.
• As you add each interface element or feature, add
  features to your test project to exercise the new
  functionality.
• Compile your DLL and test it with all potential
  target applications.

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Any Questions?
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ActiveX EXE Out-Process Components

• Components run in their own process
• It can run as stand-alone applications
• And it can also be
• executed through
• automation locally
• or remotely
• Can have GUI but
• not shown in automation

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ActiveX EXE

• Creating an ActiveX EXE component is more or less
  similar to creating an ActiveX DLL
• But use ActiveX EXE project

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Differences between DLL and EXE

• EXE is more likely to have a GUI supporting
  stand-alone execution
• Use Main as a start-up object
• Test EXE components in a separate test project,
  usually a Standard Exe project

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ActiveX Documents

• Something like VB forms but more like an
  application
• Can appear in Internet explorer but contain no
  HTML
• Can package in either DLL or EXE
• Can be read or activated by an ActiveX enabled
  container such as VB, MSOffice Binder and
  Internet Explorer
• Internet Explorer is the only browser with
  ActiveX capability at the moment

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• Active document example

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Component-based Database Programming
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Visual Basic and Databases

• VB provides capabilities to access and manipulate
  the contents of various databases created by many
  popular software packages
• VB also provides capabilities to create front-end
  GUIs to display and edit the contents of various
  databases
• These functionalities are achieved through
• An ADO (ActiveX Data Object) Data Control that
  acts as a bridge between a VB application and a
  database.
• Several data-aware controls such as DataList,
  DataGrid and DataCombo to present different views
  to the data

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ADO Data Control

• The ADO data control manages the connection
  between a database and other controls in the
  application
• It can access data stored in a variety of data
  sources and formats, such as a database, a
  spreadsheet, or even a text file
• It can also query tables or joined tables to
  retrieve selected data

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Using the ADO Data Control

• Add ADO data control to VB toolbox
• Attach an object of ADO data control to a form
• The buttons move the data control to the
  beginning, end and next records in the database

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Visible vs Enabled

• If an application never allows the user to
  interact with the ADO data control, then you
  should hide the control.
• If an application allows the user to interact
  with the ADO data control when a certain
  condition is met, then you should disable the
  control and enable it when the condition is met

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Connecting ADO to a DB

• Specify the source of connection
• Typically, using Connection String to provide
• The DBMS type
• The DB name
• The location
• Security configuration

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Set DBMS Provider
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Set Connection
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Accessing Data in a DB

• The data that can be accessed via an ADO control
  is configurable.
• This provides a powerful feature for the ADO
  control enable different users to access and
  use different set of data from the same database.
  
• The RecordSource Tab in the Property Pages is
  used to specify what data will be accessed.

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Accessing Data in a Table

• Use the adCmdTable Command object to specify a
  table in the database that would be accessed and
  viewed.

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Accessing Data from a Query

• Use the adCmdText Command object to specify an
  SQL query that will access and view a subset of
  the data in the database.

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Configuring an ADO Connection

• Set other properties including visible, timeout,
  username and passwords, etc.
• Little or no coding is required, only the use of
  the properties window.
• Once the DB and table have been identified, the
  information can be displayed on the interface.

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Recordset, Field Objects Fields Collection

• Recordset object - the collection of records
  selected by the ADO data controls RecordSource
  property
• Each field contained within the Recordset object
  is referred to as a Field object
• The collection of Field objects within a
  Recordset object makes up the Fields collection

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Example Recordset, Field Objects Fields
Collection
For example the select from Authors command
will create the following Recordset object, Field
objects, and Fields collection Recordset object
All records stored in the table Fields
collection Au ID, Author, Year Born
3 Field objects
To refer to a field within the Fields collection
adocontrol.Recordset.Fields(fieldname)
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Methods of the Recordset Object
AddNew Add a new, blank record to the end of the
recordset CancelUpdate Cancel changes made to
the current record Delete Delete the current
record from the recordset MoveFirst Move the
record pointer to the first record
MoveNext Move the record pointer to the next
record Update Save the changes made to the
current record
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Recordset Objects EOF/BOF Property

• EOF - test for the end of the recordset
• True if the record pointer is positioned after
  the last record in the recordset otherwise, the
  property contains False
• BOF test for the start of the recordset
• Used to detect record position and decide
  termination
• Private Command1_Click
• If (NOT adodc1.Recordset.EOF) Then
• adodc1.Recordset.MoveNext
• Else MsgBox (Already at last record - Cannot
  move beyond this!)
• End If
• End Sub

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Syntax of Recordset Objects Methods and
Properties

• The syntax for invoking a method of the Recordset
  object is
• adocontrol.Recordset.method
• The syntax for referring to a property of the
  Recordset object is
• adocontrol.Recordset.property.

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ADO Data Controls Refresh Method

• adocontrol.Refresh
• To create a new Recordset object while an
  application is running, you need first to enter,
  into a code window, an instruction that resets
  the ADO data controls RecordSource property. You
  then need to use the ADO data controls Refresh
  method to reopen the database and recreate the
  Recordset object

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Adding or Deleting a Record

• To delete a record the following VB command can
  be used
• adodc1.Recordset.Delete
• To add a record (to the end of a table) the
  following commands are required
• adodc1.Recordset.AddNew - creates a new blank
  record
• adodc1.Recordset.Fields(field name)New Data
  -specify the data
• adodc1.Recordset.Update - Save the new record to
  the DB table

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Example - Adding names to a DB

• The following screen allows the user to enter
  details of a new entry to a DB.
• The code attached to the Add Details button takes
  the information from the text boxes and updates
  the MS Access DB.

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Example - Adding names to a DB

• The code attached to the button Add Details would
  look like
• Private Sub CmdAdd_Click()
• adodc1.Recordset.AddNew
• adodc1.Recordset.Fields("LastName")
  txtSurname.Text
• adodc1.Recordset.Fields("FirstName")
  txtForename.Text
• If ((txtSurname.Text ltgt "") And (txtForename.Text
  ltgt "")) Then
• adodc1.Recordset.Update
• Else MsgBox ("You must enter some data!")
• End If
• End Sub

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Editing Records

• To edit a record, make sure first of all that it
  is the record currently being displayed.
• The following command tells VB that the record is
  about to be edited
• adodc1.Recordset.Edit
• Assign new data to the specific field whose
  contents you wish to change as follows
• adodc1.Recordset.Fields(field name) New
  Data
• Lastly, the update must be saved to the database
• adodc1.Recordset.update

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Data-aware Controls
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Data-aware Controls

• Refer to the controls for displaying and
  manipulating data in databases, including
  CheckBox, ComboBox, DataCombo, DaraGrid,
  DataList, FlexGrid, ListBox, PictureBox, Image,
  etc.
• Common key properties include DataSource,
  DataField, DataFormat, DataMember

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Key Common Properties
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Binding Controls

• Connecting a data-aware control to an ADO data
  control is called binding, and the connected
  controls are referred to as bound controls, which
  usually involves
• Set the controls DataSource property to the name
  of the ADO data control
• Set the controls DataField property to the name
  of a field in the database
• Always set the DataSource property before setting
  the DataField property

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DataGrid Control

• Display a table representing records and fields
  from a recordset object
• Add, update, edit and delete records
• Can be quickly configured at design time with no
  code
• Automatically display data from recordset if
  DataSource property is set at design time
• DataSource property can be set programmatically,
  able to view different tables or recordset from
  different queries

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Example Scenario
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Using ADO and DataGrid
Two controls
No code
Configure properties
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Example (cont.)
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Example Displaying a Query Results
Input a query statement
Perform the query
Show the results
The ADO control
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Set Properties at Design Time

• Connecting String
• ProviderMicrosoft.Jet.OLEDB.3.51Persist
  Security InfoFalseData SourceC\Program
  Files\Microsoft Visual Studio\VB98\BIBLIO.MDB

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Code
Set the default query
Set the runtime query
Query the database
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DataList and DataCombo Controls

• Similar to standard ListBox and ComboBox controls
• Can be automatically filled from a database field
  from the data control to which they are bound
• Many other properties that provide flexibility
  for database application, such as
• Pass a selected field to a second data control,
  making them ideal for "lookup table" applications
  
• Link database tables

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Database Introduction
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Example Scenario

• GUI includes a DataCombo, a DataList, a DataGrid
  and a button
• Functions it allows a user to select an author
  and display its books ISBN, select an ISBN and
  display some information about the book.

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Set properties at design time
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Example Code
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• Screenshots

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Summary

• ActiveX code components
• Create code components in VB
• ADO (ActiveX Data Object) data controls
• Data-aware controls
• Data manipulation in VB

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