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What is DLL (Dynamic-linked library)?

By Dinesh Thakur

(Dynamic-linked library) In programming, a type of LIBRARY file that becomes LINKED to a program that uses it only temporarily when the program is loaded into memory or executed, rather than being permanently built-in when the program is COMPILED. The same DLL may therefore be shared by many different programs, rather than each program having to contain its own copy; this saves on memory usage and potentially simplifies the updating of programs.

Microsoft WINDOWS was the first operating system to make heavy use of DLLs, with large parts of the operating system itself (e.g. KERNEL32.DLL) and of Microsoft Office applications existing in DLL format. The use of DLLs should simplify the distribution of updates to programs, but in practice they are a double-edged weapon, as installing new programs can cause chaos by overwriting DLLs needed by others with incompatible versions

What is OLE (object linking and embedding)?

By Dinesh Thakur

OLE definition is that, OLE (pronounced as oh-leh) was originally mean as ‘object linking and embedding‘, it is a Microsoft compound document technology based on Component Object Model (COM), It is introduced into Microsoft Windows 3.1. ‘OLE (object linking and embedding)‘ gives all Windows applications a standard way to create compound documents that create objects within one microsoft application and embed them into other document. OLE object meaning is graphic,spreadsheet,msword, etc. that can be embedded into a document called the “container application.” If the object allowed to be edited, the application associated with it is called “server application“. [Read more…] about What is OLE (object linking and embedding)?

What is compile time?

By Dinesh Thakur

This phrase has two meanings. Compile time can refer to how long it takes to compile a given program (see the entry above). The compile time for a program depends on how long and complicated the program is, the speed of the computer, and the quality of the compiler.

The other meaning of compile time has to do with events that happen at the time a program is compiled, or “at compile time.” A programmer may say, “Specific values are assigned to those variables at compile time.”

What is ActiveX Database Objects (ADO)?

By Dinesh Thakur

A Microsoft OBJECT LIBRARY that provides extensible, object-oriented access to data held in a variety of formats. It is intended to supplant the firm’s earlier database access libraries DATA ACCESS OBJECTS and ROO, and is employed by both MICROSOFT TRANSACTION SERVER and INTERNET INFORMATION SERVER as their main means of retrieving data from both local and remote databases.

What is ActiveX?

By Dinesh Thakur

A format developed by the Microsoft Corporation for implementing object-oriented software components. ActiveX controls are prefabricated components based on Microsoft’s COM object model, which can be employed to create new applications with little or no programming, for example by simply dragging-and-dropping them into a document, or by downloading them into a browser from a web site.

The VISUAL BASIC programming language works by dragging different ActiveX controls onto a blank container, and then writing a minimal amount of code to connect them together. There is a large market in such prefabricated controls, many written by vendors other than Microsoft, with spreadsheets, text editors, picture viewers, sound players and many other functions available ready to run.

What is alert box?

By Dinesh Thakur

An alert box is a message that appears on the screen to warn you of some imminent disaster, or to inform you of a situation in which your actions may have irreversible consequences.

For example, if you’ve just chosen the command to delete a file, an alert box might warn you that the file will be gone forever, and ask you if you really want to delete it. You have to deal with the alert box before you can move on with your life, meaning your only option when you see something like this is to click one of the buttons it offers you. Typically the dark-bordered button (which is the default button) is the safest option available-and because it’s the default, you can hit the Return or Enter key instead of clicking the button. If the alert is telling you the computer crashed, then the button may not even work, in which case you just have to turn off your machine by its switch or, if you have one, press your reset switch

Explain deference between a data control and data-bound control

By Dinesh Thakur


Data control

Data-bound

Using data control is a two-step process. First you place a data control on a form and set the properties to link it to a database file and table

You create the controls, such as labels and text boxes, to display the actual data. Each control is a bound to particular field in the table. In this example the label is called a data bound control and automatically displays the contents of bound field when the project runs.

Data control generally links one form with one table.

If you want to have data-bound controls on second form, you must place a data control on that form.

Prefix of data control is “dat”

For data-bound control prefix depends upon the control which you are using.

Data control to work you need to set some properties to connect with database like connect property, database name property, record source property.

To display data on the data-bound control that you are using like labels or textboxes. You need set it?s data source property and data field name which is column name form the table.

 

 

Which controls can be data bound

By Dinesh Thakur

1. You can bound data to data bound controls like Labels, Text Boxes, Checkbox. If you don?t want user to change the data you use Label control, where user can only view the data else you can use Text boxes.

 

2. If you want to display data in the form of True or False you can have Check Box control.

 

Explain how BOF and EOF properties are set and how they might be used in a project

By Dinesh Thakur

1. Two handy properties of the record set are BOF (beginning of file) and EOF (end of file). The BOF property is automatically set to true when the record pointer is before the first record in the record set.

This condition happens when first record is current and the user choose MovePrevious. The BOF property is also true if the record set is empty

 

2. The EOF property is similar to BOF; it is true when the record pointer moves beyond the last record in the record set and when the record set is empty.

 

3. When you are doing your own navigation in code, you need to check for BOF and EOF so that run-time errors do not occur. If the user clicks MoveNext when on the last record, what do you to do? Have the program cancel with a run time error? Display a message? Wrap around the first record? Keep the record pointer to last record?

 

4. In the following example, we will wrap-around method. If the user clicks on the MoveNext button from the end of the table, the first record becomes active record.

 

Private Sub cmdNext_Click()

„Move to Next record

datBooks.Recordset.MoveNext

If datBooks.Recordset.EOF Then

datBooks.Recordset.MoveFirst

End If

End Sub

 

What are the steps needed to add a new record to database

By Dinesh Thakur

1. When you want to add new record you have couple of choices. If you are using data control?s navigation buttons, you can allow Visual Basic to do the adds automatically. Set the data control?s EOF action property to

 

2 – AddNew. When the user moves to end of the file and clicks the arrow buttons, the Update method is automatically executed and the new record is added.

 

2. You need a different approach when you use code to accomplish record navigation. Assume that you have a command button to menu choice to add a new record. In the click event for the command button use AddNew method:

 

3. datBooks.Recordset.AddNew

 

4. When this statement executes, all bound controls are cleared so that the user can enter the data for the new record. After the data fields are entered, the new record must be saved in the file. You can explicitly save it with an update method; or, it the user moves to anther record, the update method is automatically executed.

 

5. You may want to use two buttons for adding a new record –an Add button and s save button. For the Add button, use an AddNew method; for the Save button, use the Update method.

 

6. When adding new records, some conditions can cause errors to occur.

 

7. For example, if the key field is blank on a New record, a run time error holts the program execution.

 

What are the steps needed to delete a record from database

By Dinesh Thakur

1. The delete method deletes current record. The user should display the record to delete and click a Delete command button or menu choice.

 

2. When a record is deleted, the current record is no longer valid. Therefore, a delete method must be followed by MoveNext method.

 

With datBooks.Recordset

.Delete

.MoveNext

End With

 

3. But what if the record being deleted is the last record in the table?

 

4. Remember that if the navigation buttons are used to navigate, moving beyond EOF just resets the current record to the last record.

 

What steps are needed to change the data in a database

By Dinesh Thakur

The record set object has an Update method, which you can use to save any changes in the data.

Most of the time, updating is automatically executes the Update method any time the user clicks one of the navigation buttons or one the Move methods executes.

When would it be a good idea to use a grid control

By Dinesh Thakur

Database tables can be bound to controls, such as text box, labels, checkbox and list boxes. But it displays one row data at a time.

But if you want to display multi row data then there is another good way to display data that is, data can be displayed in table in rows and columns format.

 

Visual Basic comes with several grid controls. In addition, many companies sell powerful grid controls that you can include in your project.

 

When does a control’s Validate event occur? How is the Cancel argument used

By Dinesh Thakur

When you want to make sure that a required field has an entry or that field has valid data, the Validate event is good location to check. If the field is not valid, you can display an error message and cancel the operation.

 

New Visual Basic 6, most controls now have a new property and a new event that greatly aid in validating the entries in controls. The Causes Validation property can be set to True or False, which indicates whether validation event occurs for the control just before it loses the focus.

 

For example, assume you have txtISBN and txtTitle. The user is expected to enter a value in txtISBN and tab to txtTitle. If you have the Causes Validation property of txtTitle set true, then the validate event of txtISBN will occur. Of course, the user may do something else, such as click in a different field, o a command button. You must set the Causes Validation property to true for all controls. Default setting for Causes Validation property is true.

 

Syntax of Validate Event is:-

Private Sub ControlName_Validate(Cancel As Boolean)

Over here Cancel Argument decides whether focus should be kept or not.

 

What is a record set ? What are its type ? Explain

By Dinesh Thakur

Recordset:

 

The current group of records associated with a data control; may be a table recordset , a dynaset, or a snapshot.

 

Visual Basic supports 3 kinds of Record Set as follows:-

 

Table Record Set:-

 

Table Record Set represents a single table as it exist in a Database file. Table Record Set are usually updatable unless the file is locked or open for read only.

 

Dynaset:-

 

A Dynaset is temporary set of data taken from one or more table in the form one of many table in the underlined file. A Dynaset may be a query. That was defined in a access of table of result of joining multiple tables. Like a table, a Dynaset is updatable if file is not locked or open for read only. Data in Dynaset is live that is any changes made to data as project is executing will appear in Record Set.

 

Snapshots:-

 

Snapshot Record Set, like a dynaset, may be taken from one or more table. The difference is that snapshot is not updatable and also not live. A snapshot is like photograph a picture of reality a give point. TYBSC (IT) Visual Basic 2

 

What is SQL, and how is it used in Visual Basic

By Dinesh Thakur

Visual Basic uses Structured Query Language (SQL) to create new dynasets. SQL is an Industrial Standard language for processing relational database.

 

Visual Basic uses SQL to create new recordsets.Set the data controls RecordSource property to an SQL query and execute a Refresh method

Visual Basic use SQL to select fields and records from a table and join the fields from row tables.

 

Syntax:

 

Select [ distinct ] FieldList From TableNames

Where SearchConditions

Group By FieldList

Having GroupCriteria

Order By FieldList

 

Example:

 

Select * From Books

Select * From Books, Subjects

Where Books.Subject_Code = Subjects.SubjectCode

Order By Title

Select Distinct Author from Books

 

What is grid control ? How will you create it

By Dinesh Thakur

The Databound grid control in VB 6.0 adds power and flexibility to your DataBase programs. you can easily provide grid access to any available DataBase.

You can provide simple display only access for used with summary data and on-screen reports.You can also provide editing capability to your dara grid including modifying only, add rights or delete rights.

 

It’s very easy to create a data grid form

A Grid Control-Step-by-Step

 

STEP 1: Begin a new project and widen the form.You may want to close the Project Explorer an Form Layout windows and float the properties

window to allow room to work on the wide form.

 

STEP 2:Add a data control along the bottom of the form.Set the control’s Name property to datBooks and its DatabaseName property to RnrBooks.mdb.Set the

RescordSource property to Books and verify that the RecordsetType is 1 – Dynaset.

 

STEP 3:Select project/Components to display the Components dialog box.Then locate Microsoft Data Bound Grid Control 5.0, select it , and close the dialog box.You should see the new tool in the toolbox.

 

STEP 4:Click on the DBGrid tool and draw a large grid on the form.Then , using the properties window , change the control’s Name property to dgbBooks and its DataSource property to datBooks.

 

STEP 5:Create the menu bar. It should have a File menu with only an Exit command.

 

STEP 6:Create the large label at the top of the form with the form’s title: Book List.Change the font and size to something like.

 

What is the purpose of record count and absolute position properties

By Dinesh Thakur

You can use the Record count and absolute position properties of the Data Control Recordset to display the RecordNum and RecordCount when viewing DataBase Records.

 

 

Example:

 

Record 10 of 45

 

The RecordCount property holds the number of records in a recordset.The absolute position holds the position of the current Record in the Recordset.However absolute postion is zerobased i.e; the first record has an absolute position of 0.Therefore, you must add 1 to the proprty to produce the RecordNum.

 

Example:

 

IntCurrentRecord = Data1.Rescordset.Absolute postion + 1

You cannot use the absolute position property as a record Num , because the position num changes as records are added and deleted.

 

Example:

 

Private sub Record Num( )

Dim RecordCount, CurrentRecord as integer

RecordCount = Data1.Recordset.RecordCount

CurrentRecord = Data1.Recordset.Absolute Position + 1

If Data1.Recordset.eof then

Data1.Caption = “EOF”

else

Data1.Caption = ” Record ” & CurrentRecord & ” of ” & RecordCount

Endif

End sub

 

Seek method

By Dinesh Thakur

The fastest way to search for a particular record is to use the Seek method , which can be used only with a table recordset tab.The Seek method uses indexes for the search , which is much faster than checking every record in the table as you do in a find .

 

In order to do a seek , the field on which you search must be defined with an index.

Syntax:

Data1.Recordset.Seek ComparisonOperator , FieldValue

The comparison operator must be enclosed in quotation marks and can be any one of this “=”,”>=”,”>”,”<=”,”<“.The field value is the actual value for which to search string literal must be enclosed in quotation marks;numeric values must not be so enclosed.

Example:

i. Data1.Recordset.Seek “=”, “0-671-66398-4”

ii.Data1.Recordset.Seek “>=”, 1 ‘find first record greater than or equal to 1 in the first position of the key

 

 

How can we write methods for a new class

By Dinesh Thakur

To hold the internal data of our class create private variables in the general declaration of the class modules. Then we have to deign which properties we want to write access. We can decide these things using property get and property let procedures.

 

A property get is like a function that returns the information about. The property let is like a procedure we can use to set information in the private variables.

The way that our class allows its property to be set is through property let property and to retrieve the value of a property from a class, we must use property get procedure.

The property let and property get procedure and retrieve the property value to provide member to the class module.

 

Syntax for get procedure:-

 

(Public) property get procedure_name(Optional argument list) as datatype

Statements in procedure

Procedure_name = property_name

End procedure

 

Property procedure are public by default, so we can omit the optional public keyword. We can also define a property to be private which means that the property is available only inside a class module.