1. What are the three main differences between flexgrid
control and dbgrid(Data bound Grid) control?
Ans. The Microsoft FlexGrid (MSFlexGrid) control displays
and operates on tabular data. It allows complete flexibility to sort, merge,
and format tables containing strings and pictures. When bound to a Data
control, MSFlexGrid displays read-only data.Adaptation to existing Visual Basic
code for the data-bound grid (DBGrid).
dbgrid is A spreadsheet-like bound control that displays a
series of rows and columns representing records and fields from a Recordset
object.
The data grids are bound controls; that is, they require a
data source that actually connects to a database and retrieves their data. And
it seems that the root of the problem with DBGrid is that there’s no data
source that can be readily included along with the DBGrid control.
In Visual Basic, the solution is simply to include the Data
Control on the same form as DBGrid. But the Data Control is an intrinsic
control; it’s unavailable to anything outside of the Visual Basic environment
itself. and VB 6.0 has a new set of data controls (DataGrid, DataList,
DataCombo, MSHFlexGrid, MSFlexGrid) that once again are bound controls. Unlike
DBGrid, though, they support OLE DB, and therefore rely on the an ADO Data
Source (and in particular the ActiveX Data Objects Data Control, or ADO DC) for
data access. Unlike the Data Control, the ADO
DC is a custom control (that is, an .OCX) that can be added
to any project. In short, if you add ADO DC to your project along with the
DataGrid control.
2. ActiveX and Types of ActiveX Components in VB ?
Ans. Standard EXE
ActiveX EXE
ActiveX DLL
ActiveX
document
ActiveX
Control
3. What is difference between inprocess and out of process ?
Ans. An in-process component is implemented as a DLL, and
runs in the same process space as its client app, enabling the most efficient
communication between client and component.Each client app that uses the
component starts a new instance of it.
An out of process component is implemented as an EXE, and
unlike a dll, runs in its own process space. As a result, exe’s are slower then
dll’s
because communications between client and component must be
marshalled across process boundaries. A single instance of an out of process
component can service many clients.
4. Advantage of ActiveX Dll over Active Exe ?
Ans. ACTIVEX DLL:
=============
An in-process component, or ActiveX DLL, runs in another
application’s process. In-process components are used by applications or other
in-process components. this allows you to wrap up common functionality (like an
ActiveX Exe).
ACTIVEX EXE:
=============
An out-of-process component, or ActiveX EXE, runs in its own
address space. The client is usually an application running in another
process.The code running in an ActiveX Exe is running in a separate process
space. You would usually use this in N-Tier programming.
An ActiveX EXE runs out of process while an ActiveX DLL runs
in the same process space as VB app. Also, and ActiveX EXE can be run
independent of your application if desired.
5. Explain single thread and multithread thread apartments?
Ans. All components created with Visual Basic use the
apartment model, whether they’re single-threaded or multithreaded. A
single-threaded component has only one apartment, which contains all the
objects the component provides.
This means that a single-threaded DLL created with Visual
Basic is safe to use with a multithreaded client. However, there’s a
performance trade-off for this safety. Calls from all client threads except one
are marshaled, just as if they were out-of-process calls.
6. What is a Component?
Ans. If you compile an ActiveX dll, it becomes a component.
If you compile an ActiveX Control, it becomes both a
component and a control. Component is a general term used to describe code
that’s grouped by functionality. More specifically, a component in COM terms is
a compiled collection of properties/methods and events.
Typically a component is loaded into your project via the
References whereas an ActiveX Control is loaded into your project via
“components”.
7. What is meant by “Early Binding” and “Late Binding”?
Which is better?
Ans. Early binding and late binding refer to the method used
to bind an interface’s properties and methods to an object reference
(variable). Early binding uses type library information at design time to
reference procedures, while late binding handles this at run time. Late binding
handles this by interrogating the reference before each call
to insure that it supports a particular method. Since every call to a late
bound
object actually requires two calls
(”Do you do this?” followed by “Okay, do it then”), late
binding is much less efficient than early binding. Except where early binding
is not supported (ASP, scripting, etc.), late binding should only be used in
very special cases.
It is a common misconception that any code using the
CreateObject function instead of Set = New is using late binding. This is not
the case. The type declaration of the object variable determines whether
it is late or early bound, as in the following:
Dim A As Foo
Dim B As Foo
Dim C As Object
Dim D As Object
Set A = New Foo ‘Early Bound
Set B = CreateObject(”FooLib.Foo”) ‘Early Bound
Set C = CreateObject(”FooLib.Foo”) ‘Late Bound
Set D = New Foo ‘Late Bound
8. What are the Advantages of disconnected recordsets?
Ans. A disconnected Recordset, as its name implies, is a
Recordset that lacks a connection.
seen that a Recordset that does not have a database
connection can be very useful as a tool in your programming. It can save you
time and effort and make your code more scalable.
In order to create a disconnected Recordset two Recordset
properties must be set appropriately.
It is a requirement that the CursorLocation property is set
to adUseClient and the LockType property is set to adLockBatchOptimistic. Note
that the CursorType will default to adUseStatic if we don’t explicitly state
that it should be set to adUseClient.) i.e
rst.LockType = adLockBatchOptimistic
rst.CursorLocation = adUseClient
However, we’ve recently discovered that these steps aren’t
necessary. VB automatically assigns batch optimistic locking to newly created,
connectionless recordsets. And, of course, without a
connection, a recordset can’t have any other cursor but a client-side one. To
create one of these structures, then, the only thing you need do is create
the object variable instance. After that, you can simply
begin adding fields to the construct.
To add fields, you use the Fields collection’s Append
method. This method requires two parameters , the field name and the field data
type. So, to create a connectionless recordset with two fields,you’d use code
similar to:
Dim rst As ADODB.Recordset
Set rst = New ADODB.Recordset
rst.Fields.Append “CustID”, adVarChar
rst.Fields.Append “CustName”, adVarChar
Additional, optional Append method parameters include
DefinedSize and Attrib. The DefinedSize argument takes the size of the field.
Fill the Attrib parameter with constants that define additional field
characteristics, such as whether it will allow null values or is updatable.
Since, in our technique, we want the fields to mirror the
structure of the original recordset, we’ll simply use existing values for these
parameters.
Disconnected Recordsets, first available with ADO 2.0, are
the most commonly used mechanism to retrieve a Recordset and open a connection
for only the necessary amount of time, thus increasing scalability. They are
call disconnected because the connection to the database is closed.
The collections, properties, and methods of a disconnected
Recordset are still available even though the connection is closed. This frees
up server resources, given that the number of open connections is limited and
database locking is a non-issue.
9. What are Benefits of wrapping database calls into MTS
transactions?
Ans. If database calls are made within the context of a
transaction, aborting the transaction will undo and changes that occur within
that transaction.
This removes the possibility of stranded, or partial data.
Transaction that uses the Microsoft® Transaction Server (MTS) environment. MSMQ
implicitly uses the current MTS transaction if one is available.
BENIFTIS OF USING MTS :
Database Pooling, Transactional operations, Deployment,
Security, Remote Execution This allows MTS to reuse database connections.
Database connections are put to ?sleep? As opposed to being created and
destroyed and are activated upon request.
10. How to register a component?
Ans. Compiling the component, running REGSVR32 MyDLL.dll
11. Controls which do not have events ?
Ans. Shape and line controls are useful for drawing
graphical elements on
the surface of a form. These controls don’t support any
events; they
are strictly for decorative purposes.
The image, shape and line controls are considered to be
lightweight controls; that is, they support only a subset of the properties,
methods, and events found in the picture box. Because of this, they typically
require less system resources and load faster than the picture box control.
12. What are the Control Categories?
Ans. a)Intrinsic controls:
such as the command button and frame controls. These
controls are contained inside the Visual Basic .exe file. Intrinsic controls
are always included in the toolbox
b)ActiveX controls:
which exist as separate files with a .ocx file name
extension. These include controls that are available in all editions of Visual
Basic (DataCombo, DataList controls, and so on) and those that are available
only in the Professional and Enterprise editions (such as Listview, Toolbar,
Animation, and Tabbed Dialog). Many third-party ActiveX controls are also
available.
c)Insertable Objects:
such as a Microsoft Excel Worksheet object containing a list
of all your company’s employees, or a Microsoft Project Calendar object
containing the scheduling information for a project. Since these can
be added to the toolbox, they can be considered
controls.Some of these objects also support Automation (formerly called OLE
Automation),which allows you to program another application’s objects from
within a Visual Basic application.
13. What is the difference between Image and Picture box
controls?
Ans. The sizing behavior of the image control differs from
that of the picture box. It has a Stretch property while the picture box has an
AutoSize property. Setting the AutoSize property to True causes a picture box
to resize to the dimensions of the picture; setting it to False causes the
picture to be cropped (only a portion of the picture is visible). When set to
False (the default) , the Stretch property of the image control causes it to
resize to the dimensions of the picture.
Setting the Stretch property to True causes the picture to
resize to the size of the image control, which may cause the picture to appear
distorted.
14. What is the Default property of datacontrol ?
Ans. connect property.
15. Define the scope of Public, Private, Friend procedures?
Ans. The set of public variables, methods, properties, and
events described in a class module define the interface for an object. The
interface consists of the object members that are available to a programmer
who’s using the object from code.
You can create private variables, methods, properties, and
events that are used by other procedures within the class module but are not
part of the object’s public interface. Additionally, constants user-defined
types, and Declare statements within a class module must always be private.
The Friend keyword makes a procedure private to the project:
The procedure is available to any code running within the project, but it is
not available to a referencing project.
16. Describe Database Connection pooling relative to MTS ?
Ans. This allows MTS to reuse database connections. Database
connections are put to ?sleep? as opposed to being created and destroyed and
are activated upon request.
Object pooling is an important design concept required for
high-performance applications. A performance optimization based on using
collections of preallocated resources, such as objects or database connections.
Pooling results in more efficient resource allocation.
17. What is the Difference between a function and a
subroutine ?
Ans. A function accepts any number of parameters (possibly
zero), does something with them, and returns a value. A subroutine is performs
an action, but doesn’t return a value.
There are two differences between a function and a
subroutine: A)How they are invoked. B)How they are accessed.
A function call has the following syntax ::
function(arg1, arg2, …)
where: function Is the name of the function. arg1, arg2, …
Are the arguments.
A subroutine call has the following syntax
::subroutine (arg1, arg2, … {outputfield|’format’})
where: subroutine –>Is the name of the subroutine. arg1,
arg2, … Are the arguments. {outputfield|’format’} Is the name of the output
field or its format.
In addition, on some platforms, the functions are available
immediately; whereas, the subroutines are available in a special subroutine
library that you must access.
18. What is the Difference between Linked Object and
Embedded Object?
Ans. Embedding objects -
When you embed an object, a copy of the object is inserted
into the destination document. There’s no link to the original file. When you
change information in the source document, no changes will be reflected in the
destination document. The actual data for the object is stored within the
destination file. To make changes to the embedded object, double click it and
it will launch the original application the source file was in.
Linking objects -
Information is updated when you modify the original source
file when you use a linked object. This dynamic updating is very handy for
things such as the aforementioned monthly report. You can open up the Excel
spreadsheet that is referenced within your Word document.Make changes to the
spreadsheet, close Excel, and when you open your Word document… viola! The
changes are already there. If that object is linked to ten other Word files,
the changes are already in those ten files, too! actually linking or embedding
an object is fast and easy.
19. What is the Difference between listbox and combo box?
Ans. A LISTBOX CONTROL displays a list of items from which
the user can select one or more. If the number of items exceeds the number that
can be displayed, a scroll bar is automatically added to the ListBox control. A
COMBOX CONTROL combines the features of a text box and a list box. This control
allows the user to select an item either by typing text into the combo box, or
by selecting it from the list.
DIFF::Generally, a combo box is appropriate when there is a
list of suggested choices, and a list box is appropriate when you want to limit
input to what is on the list. A combo box contains an edit field, so choices
not on the list can be typed in this field.
20. What is the Difference between Dynaset and Snapshot?
Ans. All Recordset objects are constructed using records
(rows) and fields (columns). There are five types of Recordset objects:
Table-type Recordset:
representation in code of a base table that you can use to
add, change, or delete records from a single database table (Microsoft Jet
workspaces only).
Dynaset-type Recordset:
the result of a query that can have updatable records. A
dynaset-type Recordset object is a dynamic set of records that you can use to
add, change, or delete records from an underlying database table or tables. A
dynaset-type Recordset object can contain fields from one or more tables in a
database. This type corresponds to an ODBC keyset cursor.
Snapshot-type Recordset:
a static copy of a set of records that you can use to find
data or generate reports. A snapshot-type Recordset object can contain fields
from one or more tables in a database but can’t be updated. This type
corresponds to an ODBC static cursor.
Forward-only-type Recordset:
identical to a snapshot except that no cursor is provided. You
can only scroll forward through records. This improves performance in
situations where you only need to make a single pass through a result set. This
type corresponds to an ODBC forward-only cursor.
Dynamic-type Recordset:
a query result set from one or more base tables in which you
can add, change, or delete records from a row-returning query. Further, records
other users add, delete, or edit in the base tables also appear in your
Recordset. This type corresponds to an ODBC dynamic cursor (ODBCDirect
workspaces only).
21. What is the Difference Listindex and Tab index?
Ans. LIST INDEX:
Returns or sets theindex of the currently selected item in
the control. Not available at design time.Default LIST INDEX IS -1 for
ComboBox, DirListBox, and DriveListBox controls
TAB INDEX:
Returns or sets thetab order of most objects within their
parent form. Visual Basic automatically renumbers the TabIndex of other
controls to reflect insertions and deletions. You can make changes atdesign time
using theProperties window or atrun time in code.The TabIndex property isn’t
affected by the ZOrder method.
22. What is the Difference modal and moduless window?
Ans. MODAL forms are forms which require user input before
any other actions can be taken place. In other words, a modal form has
exclusive focus in that application until it is dismissed. When showing a modal
form, the
controls outside this modal form will not take user
interaction until the form is closed. The internal MsgBox and InputBox forms
are examples of modal forms. To show a form modally, use the syntax:
MyForm.SHOW.vbModal ‘ a predeclared constant for 1
MODELESS forms are those which are shown but do not require
immediate user input. MDI child forms are always modeless. To show a form modeless,
use the syntax:: MyForm.SHOW
23. What is the Difference Object and Class?
Ans. Classes and objects are separate but related concepts.
Every object belongs to a class and every class contains one or more related
objects.
1)A Class is static. All of the attributes of a class are
fixed before,during, and after the execution of a program. The attributes of a
class don’t change.The class to which an object belongs is also (usually)
static. If a particular object belongs to a certain class at the time that it
is created then it almost certainly will still belong to that class right up
until the time that it is destroyed.
2)An Object on the other hand has a limited lifespan.
Objects are created and eventually destroyed. Also during that lifetime, the
attributes of the object may undergo significant change.So basically the
difference between a class and an object is that a class is a general concept
while objects are the specific and real instances that embody that concept.
When creating an object oriented program we define the classes and the
relationships between the classes . We then execute the program to create,
update, and destroy the objects which are the specific realization of these
classes.
24. What is the Difference Query unload and unload in form?
Ans. Occurs before a form or application closes. When an
MDIForm object closes, the QueryUnload event occurs first for the MDI form and
then in all MDI child forms. If no form cancels the QueryUnload event, the
Unload event occurs first in all other forms and then in an MDI form. When a
child form or a Form object closes, the QueryUnload event in that form occurs
before the form’s Unload event.
25. What is the Difference Declaration and Instantiation an
object?
Ans. Dim obj as OBJ.CLASS with either
Set obj = New OBJ.CLASS or
Set obj = CreateObject(?OBJ.CLASS?) or
Set obj = GetObject( ,? OBJ.CLASS?)
or
Dim obj as New OBJ.CLASS
Set object = Nothing
ensure the object is release from the memory.
If this object is a form, you can add set myform = nothing
and Form_Unload() event.Maintain a habit of remove the object by using set
object = nothing which will benefit at last.
Visual Basic is supposed to automatically release objects
when they go out of scope. To free up some memory usage, you can set the object
to
nothing.
26. Draw and explain Sequence Modal of DAO.
Ans.
Connection,Container,Database,DBEngine,Document,Error,Field,Group,Index
Parameter
Property,QueryDef,Recordset,Relation,TableDef,User,Workspace
Version |Year |Significant Changes and New Features of
Visual Basic?
1 1991 initial release, with drag and drop GUI creation
2 1992 ODBC, object variables
3 1993 Access Engine, OLE 2.0, Crystal Reports, new tools
and controls
4 1995 classes, OCXs
5 1997 compiler, ActiveX controls
6 1998 web support, windowless controls, designers, data
sources
.NET 2001 XML, SOAP, inheritance, structured exception
handling
27. How can objects on different threads communicate with
one another?
Ans. Processes communicate with one another through
messages, using Microsoft’s Remote Procedure Call (RPC) technology to pass
information to one another. There is no difference to the caller between a call
coming from a process on a remote machine and a call coming from another process
on the same machine.
Multithreaded applications must avoid two threading
problems: deadlocks and races. A deadlock occurs when each thread is waiting
for the other to do something
28. How can you force new objects to be created on new
threads?
Ans. The CreateThread function creates a thread to execute
within the virtual address space of the calling process.
To create a thread that runs in the virtual address space of
another process Creating a new thread is as easy as declaring it and supplying
it with a delegate to the method where the thread is to start. When you are
ready to begin execution on the thread, call the Thread.Start Method. There are
special considerations involved when working with multiple threads of
execution.
To create a new thread of execution
====================================
Declare the thread.
******************
‘ Visual Basic
Dim myThread as System.Threading.Thread
// C#
System.Threading.Thread myThread;
Instantiate the thread with the appropriate delegate for the
starting point of the thread. Use the AddressOf operator to create the delegate
in Visual Basic, or create a new ThreadStart object in C#.
*******************
‘ Visual Basic
myThread = New System.Threading.Thread(AddressOf
myStartingMethod)
// C#
myThread = new System.Threading.Thread(new
System.Threading.ThreadStart(myStartingMethod));
call the Thread.Start method to start the thread.
*******************
‘ Visual Basic
myThread.Start()
// C#
myThread.Start();
29. How does a DCOM component know where to instantiate
itself?
Ans. To create a remote instance of a script component, call
the CreateObject method, passing it the name of the remote computer as a
parameter. If the remotable attribute of a script component’s
<registration> element has been set to “true,” the script component can
be instantiated remotely from another computer using Distributed COM (DCOM).
Both computers must have basic DCOM installed. Note The
ability to use CreateObject for instantiating remote script components requires
Visual Basic 6.0 or later or VBScript 5.0 or later. The following Visual Basic
example shows how to do this on a computer named “myserver”:
Set newS = CreateObject(”Component.MyComponent”, “myserver”)
Note There can be a slight delay when you first instantiate a
remote script component while DCOM establishes communication between the
computers.
1. You can specify the machine on which you want to create
the remote server object in DCOM config (’dcomcnfg’).
2. You can specify the machine name when instantiating the
remote server object.
In C you can do this with a call to CoGetClassObject or
CoCreateInstanceEx (instead of CoCreateInstance, which does not allow you to
specify the name of the machine).
In VB you can specify the name in one of the parameters in
the call to CreateObject
30. What type of multi-threading does VB6 implement?
Ans. Apartment model threading
31. What is Database Connection pooling (relative to MTS)?
Ans. This allows MTS to reuse database connections. Database
connections are
put to “sleep” As opposed to being created and destroyed and
are activated upon request.
32. What is the tool used to configure the port range and
protocols for DCOM communications?
Ans. DCOMCONFIG.EXE
33. What is a Type Library and what is it’s purpose ?
Ans. The type library may represent another Visual Basic
project, or any other executable component that exposes a type library.
Visual Basic creates type library information for the
classes you create, provides type libraries for the objects it includes, and
lets you access the type libraries provided by other applications.
34. What are binary and project compatibility?
Ans. Visual Basic’s Version Compatibility feature is a way
of enhancing your components while maintaining backward compatibility with programs
that were compiled using earlier versions. The Version Compatibility box,
located on the Component tab of the Project Properties dialog box, contains
three options:
No Compatibility:
Each time you compile the component, new type library
information is generated, including new class IDs and new interface IDs. There
is no relation between versions of a component, and programs compiled to use
one version cannot use subsequent versions.
Project Compatibility:
Each time you compile the component the type library
identifier is kept, so that your test projects can maintain their references to
the component project. All class IDs from the previous version are maintained;
interface IDs are changed only for classes that are no longer binary-compatible
with their earlier counterparts. Note This is a change in Project Compatibility
from Visual Basic 5.0, where all class IDs and interface IDs in the project
changed if any one class was no longer binary-compatible.
Important For the purpose of releasing compatible versions
of a component, Project Compatibility is the same as No Compatibility.
Binary Compatibility:
When you compile the project, if any binary-incompatible
changes are detected you will be presented with a warning dialog. If you choose
to accept the warning, the component will retain the type library identifier
and the class IDs. Interface IDs are changed only for classes that are no
longer binary-compatible. This is the same behavior as Project Compatibility.
If, however, you choose to ignore the warning, the component
will also maintain the interface IDs. This option is only available when the
compiler determines that the change was in the procedure ID or signature of a
method.
Note:: When people talk about Version Compatibility, they’re
usually referring to Binary Compatibility.
How to set a shortcut key for label?
object.KeyLabel(keycode) [= string]
You would probably create the menu item as follows:
.Add “keyFile”, , , “E&xit”, , vbAltMask + vbCtrlMask,
vbKeyEnd
The default key label for vbKeyEnd is “End”. Thus, the
shortcut string will be created by default as “Ctrl+Alt+End”.
35. Name the four different cursor and locking types in ADO
and describe them briefly ?
Ans. CURSORS:
*********
The cursor types are listed from least to most resource
intensive.
Forward Only - Fastest, can only move forward in recordset
Static - Can move to any record in the recordset. Data is
static and never changes.
KeySet - Changes are detectable, records that are deleted by
other users are unavailable, and records created by other users are not
detected Dynamic - All changes are visible.
LOCKING TYPES:
****************
LockPessimistic - Locks the row once after any edits occur.
LockOptimistic - Locks the row only when Update is called.
LockBatchOptimistic - Allows Batch Updates.
LockReadOnly - Read only. Cannot alter the data.
36. Name the different compatibility types when creating a
COM component?
Ans. No Compatibility - New GUID (Globally Unique
Identifier) created, references from other components will not work Project
Compatibility - Default for a new component <Not as critical to mention this
one>
Binary Compatibility - GUID does not change references from
other components will work
Why is it important to use source control software for
source code?
Modification history. Code ownership: Multiple people cannot
modify the same code at the same time.
37. List the ADO objects?
Ans. Connection -Connects to a data source; contains the
Errors collection
Command - Executes commands to the data source. The only
object that can accept parameters for a stored procedure Recordset - The set of
data returned from the database.
Under the ADO Command Object, The Parameters collection.
collection is responsible for input to stored procedures.
38. What two methods are called from the ObjectContext
object to inform MTS that the transaction was successful or unsuccessful?
Ans. SetComplete and SetAbort.
39. What is the benefit of wrapping database calls into MTS
transactions?
Ans. Aborting the transaction will undo and changes that
occur within that transaction. This removes the possibility of stranded, or
partial data
40. Describe and In Process vs. Out of Process component.
Which is faster?
Ans. An in-process component is implemented as a DLL, and
runs in the same process space as its client app, enabling the most efficient
communication between client and component. Each client app that uses the
component starts a new instance of it.
An out of process component is implemented as an EXE, and
unlike a dll, runs in its own process space. As a result, exe’s are slower then
dll’s because communications between client and component must be marshaled
across process boundaries. A single instance of an out of process component can
service many clients.How would you declare and raise custom events in a class?
a) Public Event OnVarChange();
b) RaiseEvent OnVarChange[(arg1, arg2, ... , argn)]
41. What is the difference between a Property Let and
Property Set procedure?
Ans. Let - for simple variable
Set - for object
42. What is the difference between ANSI and UNICODE strings
when passed as arguments to a DLL?
Ans. ANSI - one byte for a char UNICODE - two bytes per char
- works only on NT
43. What is the difference in passing values ByRef or ByVal
to a procedure?
Ans. ByRef -pass the address (for string -address of address
of first byte)
BY REF IS VERY USEFULL When the contents itself are being
modified, when there is large data. Multiple arguments are needed to be
returned, instead they can be passed as reference.
ByVal -pass the value (for string -it is the address of
first byte)
44. What is the purpose of the DoEvents command?
Ans. Fields execution so that the operating system can
process other events. Returns number of open forms. Useful for things like
‘cancel search’ in Windows
Name and define the logical tiers in a traditional 3-tiered
architecture?
Presentation logic - front end (HTML, Visual Basic forms)
Business Logic - Applications and components that
encapsulate business logic
Data end - databases to store data
45. What is the difference between a PictureBox and Image
control?
Ans. Image Control - Use this to display a picture. Use it
over the PictureBox because it takes less operating system resources
PictureBox- While it can display pictures, it also acts as
an area on which you can print text and graphics. Use it for home-grown
graphics or print previews.
46. Under which circumstance does a VB application ignore a
Timer event?
Ans. When the system is really busy doing something else and
when DoEvents is being executed
47. What does the NewIndex property return?
Ans. Used to retrieve the index of the item most recently
added to a ListBox or ComboBox control.
48. What is the purpose of the ClipControls property on a
form or container?
Ans. Returns or sets a value that determines whether
graphics methods in Paint events repaint the entire object or only newly
exposed areas. Also determines whether the Microsoft Windows operating
environment creates a clipping region that excludes non-graphical controls contained
by the object. Read-only at run time.
49. What is the purpose of the AutoRedraw property on a form
or container?
Ans. Setting AutoRedraw to True automatically redraws the
output from these methods in a Form object or PictureBox control when, for
example, the object is resized or redisplayed after being hidden by another
object
50. What version control systems have you used?
Ans. TLIB 16-Bit add-in
51. How about any other database engines?
Ans. Apollo OLE DB ,Apollo Server ,Apollo SQL ,FUNCky
,R&R Report Writer.
52. What kind of components can you use as DCOM servers?
Ans. actve-x components, Com
Dim x, y as integer. What is x and y data type?
X as variant and y as integer.
53. What is the size of the variant data type?
Ans. The Variant data type has a numeric storage size of 16
bytes and can contain data up to the range of a Decimal, or a character storage
size of 22 bytes (plus string length), and can store any character text.
54. What is the return type of Instr and Strcmp?
Ans. Instr – integer (Numeric position)
Strcmp - integer ( if both the string are equal they result
= 0)
Strcmp (Str1, Str2, Comparetype)
Comparing mode = 0 – Binary Comparing
1 – Textual Comparing
55. What is the max size allowed for Msgbox Prompt and Input
Box?
Ans. 1024
Max label caption length. –
2,048
Max Text box length –
32,000
Max Control Names length –
255.
56. What is the Extensions used in Visual Basic?
Ans. Frm, bas, cls, res, vbx, ocx, frx, vbp, exe
57. What is frx?
Ans. When some controls like grid and third party control
placed in our application then it will create frx in run time.
58. What will be the result for 15/4 and 15\4 ?
Ans. 15/4 = 3.75 and 15\4 = 3
59. What is keyword used to compare to objects?
Ans. ISOperator – Returns Boolean.
60. How many procedures are in VB?
Ans. function and sub procedures. Function Will return value
but a sub procedure wont return values.
61. Where will we give the option explicit keyword and for
what?
Ans. In the general declarations section. To trap undeclared
variables.
62. What is Friend Variable?
Ans. Scope sharable between projects.What is binding? What
are types of binding?
Assigning variable with defined memory space. Late Binding -
Memory size is allotted in later stage.
Ex:- Dim x as object
Early Binding - Memory size is allotted while declaring
itself. New Key word is important.
Ex:- Dim x as New Object
63. What is the difference between Property Get, Set and
Let?
Ans. Set – Value is assigned to ActiveX Object from the
form.
Let – Value is retried to ActiveX Object from the form.
Get- Assigns the value of an expression to a variable or
property.
64. What is Mask Edit and why it is used?
Ans. Control. Restricted data input as well as formatted
data output.
Drag and Drop state numbers and functions.
State 0 – Source control is being dragged with the range of
a target.
1 – Out of the range of a target.
2 – One positon in the target to another.
65. What are the type of validation available in VB?
Ans. Field, Form
66. With in the form we want to check all the text box
control are typed or not? How?
Ans. For each currentcontrol in controls if typeof currentcontrol
is TextBox then end if next.
67. What is control array and How many we can have it with
in the form?
Ans. Group of control share the same name. Max 32, 767.What
is the default model of the form? And
68. Suppose from form1 to form2 object property settings
will arise to ?
Ans. Invalid procedure call or argument (Run time error – 5)
69. What is the diff between the Std and Class Module?
Ans. Std Global with in the project. Cls Global through out
the all project only thing is we want to set the type lib. Class Modules can be
Instantiated.
70. What are the Different type of Instantiation?
Ans. Private – Only for the Specific Module.
Public not creatable – Private & Public
Multi Use - Variable we have to declare.
Single Use – Not possible through dll.
Global Multiuse – Have variable not Required to
Declare. Global Single Use - Only for exe.
71. How to declare Dll Procedure?
Ans. Declare function “<Function Name>” lib “<Lib
Name>” Alias “<Alias Name>” (Arg, …..) as Return type.
72. What is MDI form? MDI Styles?
Ans. We can have only one MDI form for a project. Multiple
Document Interface. This form type is VBModal. We have set the Child property
of the forms to True to place forms inside this MDI.
Style availables 1. VbCascade 2. VbTitle Horizontal
73. How many images can be placed in the image list ?
Ans. 64
74. Explain different type of Datatypes?
Ans. LOB (Large Object Data type).
CLOB (Stores Character Objects).
BLOB ( Store Binary Objects such as Graphic, Video Chips and
Sound files).
BFILE(Store file pointers to LOB It may Contain filename for
photo’s store on CD_ROM).
75. What is Zorder Method?
Ans. Object.Zorder = 1 or 0 Place a Specified mdiform form
or control at the front or back of the z-order with n its Graphical Level.
76. What is diff between the Generic Variable and Specific
Variable?
Ans. Generic Variable:Create Object Ex:-Ole-Automation . No
need refer the object library.
Specific Variable: Binding Procedure Early and Late Binding
( Can be Remove from the Memory).
77. What are properties available in Clip Board?
Ans. No Properties Available. Only the methods they are
SetText, GetText, Setdata(), Getformat(), Clear.
78. What is Dll?
Ans. Libraries of procedure external to the application but
can be called from the application.
79. What is Tabstrip control? What is the starting Index
value? How to locate it?
Ans. It is tab control to place our controls with in the
form in multiple sheets.
Index starts with 1. And to identify
If Tabstrip1.SelectedItem.Index = 1 Then
…..
End if
80. Why we use Treeview Control?
Ans. To list the hierarchial list of the node objects. Such
of files and Directories.
81. Why we need OLE-Automation? Advantages?
Ans. Enables an application to exposes objects and methods
to other Applications.
No need to reserve memory. No need to write functions.
Object library that simplify programming tasks. i.e., No
need to Object library. (OLB, TLB).
82. What is the diff between the Create Object and Get
object?
Ans. Create Object - To create an instance of an object.
Get Object – To get the reference to an existing object.
83. How to create Properties and Methods for your own
Controls?
Ans. Properties – Public variable of a Class
Method – Public procedure of a classWhat is Collection
Objects?
Similarly to arrays but is preferred over an array because
of the following reasons.
1. A collection objects uses less Memory than an array.
2. It provides methods to add and delete members.
3. It does not required reason statement when objects are
added or deleted.
4. It does not have boundary limitations.
84. What is Static Variable?
Ans. Its Scope will be available through out the life time.
85. What is Implicit?
Ans. Instance of specific copy of a class with its own
settings for the properties defined in that class. Note: The implicity defined
variable is never equal to nothing.
86. What are the scope of the class?
Ans. Public , private, Friend
87. Can we able to set Instancing properties like Singleuse,
GlobalSingleuse to ActiveXDll?
Ans. No.
88. In project properties if we set Unattended what is it
mean?
Ans. This cannot have user interface. This can be used for
the COM creation.What are the Style Properties of Combo Box?
Simple, Dropdown list – We can type and select.
Dropdown Combo – Only Drop Down.
89. What are the Style properties of List Box?
Ans. Simple –Single Select , Extended. – Multiple Select.
90. What are the different types of Dialog Box?
Ans. Predefined, Custom, User Defined.
91. What is Parser Bug?
Ans. It is difficult to use database objects declared in a
module from within a form.
92. What is the Dll required for running the VB?
Ans. Vbrun300.dll
93. Can We create CGI scripts in VB?
Ans. Yes.
94. How to change the Mouse Pointer?
Ans. Screen.MousePointer = VBHourGlass/VBNormal.
95. How to check the condition in Msgbox?
Ans. If(Msgbox(”Do you want to delete this
Record”,VbYesNo)=VbYes)Then End if
96. What is difference between datagrid and flexgrid?
Ans. Datagrid – Editable.
Flexigrid – Non-Editable. (Generally used for Read only
purpose.)
97. What is ADO? What are its objects ?
Ans. ActiveX Data Object. ADO can access data from both flat
files as well as the databases. I.e., It is encapsulation of DAO, RDO, and OLE
that is why we call it as OLE-DB Technology. Objects are Connection, Record
Set, Command, Parameter, field, Error, Property.
98. What is Dataware Control?
Ans. Any control bound to Data Control.
Ex:- Textbox, Check Box, Picture Box, Image Control, Label,
List box, Combo Box, DB Combo
99. What are the locks available in Visual Basic?
Ans. Locking is the process by which a DBMS restricts access
to a row in a multi-user environment
4 types of locks. They are
1.Batch Optimistic
2.Optimistic
3.Pessimistic
4.ReadOnly
100. What is the diff between RDO and ADO?
Ans. RDO is Hierarchy model where as ADO is Object model.
ADO can access data from both flat files as well as the data bases. I.e., It is
encapsulation of DAO, RDO , OLE that is why we call it as
OLE-DB Technology.
101. How can we call Stored procedure of Back End in RDO and
ADO ?
Ans. In RDO – We can call using RDO Query Objects.
In ADO – We can call using Command Objects.
102. What is the different between Microsoft ODBC Driver and
Oracle OBDC Driver?
Ans. Microsoft ODBC driver will support all the methods and
properties of Visual Basic. Where as the Oracle not.
103. What are the Technologies for Accessing Database from
Visual Basic?
Ans. DAO, Data Control, RDO, ODBCDIRECT, ADO, ODBC API.
104. How to Call Stored Procedures in VB?
Ans. 1. Calling Simply the Procedure with out Arguments
“Call ProcedureName}”
If it is with Arguments Means then
Declare the Query Def qy
Set Qy as New Query def
Qy.SQL = “{Call ProcedureName(?,?,?)}”
qy(0)=val(Txt1.Text)
qy(1)=val(Txt2.Text)
qy(2)=val(Txt3.Text)
Set Rs = Qy.OpenresultSet
Txt(1)=Rs.RdoColumns(0)What is MAPI ?
Messaging Application programing Interface.
105. Describe Different type of Passing Value?
Ans. By value, By ref, Optional, Param Array.
Note:- Optional keyword cannot be used while declaring
arguments for a function using param array.
106. What are the different types of error?
Ans. Syntax Errors, Runtime , Logic.
107. What is Seek Method which type of record set is
available this?
Ans. Only in DbOpenTables.
Syntax: rs.index = “empno”
rs.seek “=” , 10
If with our setting the rs.index then run time error will
occur.
108. What is Centralization Error Handling?
Ans. Writing funciton and calling it when error occurs.
109. What is Handling Error in Calling chain.
Ans. This will call the top most error where the error is
handled.
110. To connect the Data Control with Back end What are all
the properties to be set?
Ans. Data source Name, Record Source Name
111. How to trap Data Base Error?
Ans. Dim x as RDOError
X(0).Des
X(1).NumberWhat is view Port?
The area under which the container provides the view of the
ActiveX Document is known as a view port.
112. What methods are used for DBGrid in unbound mode?
Ans. AddData, EditData, Readdata, WriteData.
113. How to increase the Date corresponding with
month,date,year?
Ans. DateSerial(year(Now),Month(Now)+1,1)
Hour, min, sec, month, year, DateSerial, dateadd, datediff,
weekday, datevalue, timeserial,timevalue.
Setting the Cursors.
Default Cursor – 0
ODBC Cursor (Client side) – 1
ServerSide Cursors (More Network traffic) - 2Cursor
management
Client Batch – Batch up the Multiple SQL Statements in a
single string and Send them to the Server at one time.
114. What are the RDO Methods and Events?
Ans. Methods Events
Begin Trans Validate
Commit Trans Reposition
Rollback Trans Error
Cancel Query Complied
Refresh
Update Controls
Update rowWhat is Static Cursor?
In ADO Snap Shot is called so.
115. What is Mixed Cursors?
Ans. Static + Keyset
116. What is FireHouse Cursors?
Ans. Forward Only Some time Updateable
117. What is DBSqlPassThrough?
Ans. It will By Passing the Jet Query Processor.
118. What is DBFailError?
Ans. Rolls Back updates if any errors Occurs.
119. What is RdExecDirect?
Ans. Bypasses the Creation of a stored procedure to execute
the query. Does not apply to Oracle.
RdoParameter Object RdoParameterConstant
Direction RdparamInput
RdparamInputOutput
RdParamOutput
Name
Type
Value
120. In Form_Unload Event and Form_QueryUnload, which Event
fire First?
Ans. QueryUnload.
121. What is the difference between Option Base and Option
Explicit?
Ans. Option Base: When an array is declared by default
starting index number is 0. By using this statement the programmer can change
the starting index number. But according to coding conventions this concept
should not be used.
Option Explicit: Declaring a variable in Visual Basic is not
must. By Default every variable are considered as Variant. It causes
unnecessary memory wastage. If Option Explicit is declared, every variable must
be defined. It is declared on the top of the form general declaration.
122. How many Events in a form?
Ans. 31 Events.
123. What property of Menu can not be set at runtime?
Ans. Name Property.
124. Does Visual Basic 6 support OOPS Concepts? Explain it.
Ans. It does not support Inheritance and Data Binding.
125. How to get Cursor position using API?
Ans. GetCursorPos() is the API that is used to get the
cursor position.
126. What is adUseClient and adUseServer? Where is it going
to affect in runtime?
Ans. If the CursorLocation Property is set to adUseClient,
the recordset will be available at client as disconnected recordset, where User
can do any changes on it, then using the ActiveConnection, we can connect to
the database once again and update the modifications.
If the
CusorLocation Property is set to adUseServer, the recordset is available at
server side with active connection, can perform any transaction with the
database.
127. What is OOPS? What is Polymorphism? Does VB6 supports
OOPS concept? Explain it.
Ans. OOP(s) is Object Oriented Programming.
Polymorphism is the ability to change implementation of a
defined method depending on the object in question. Polymorphism can be
achieved by abstract classes or Interfaces. Interfaces are totally Polymorphic
as they just have the concept defined but the implementation has to be done by
deriving childes.
Visual Basic 6.0 does not support Object Oriented
Programming Concepts completely.