OLE is the control used to call a windows application.
Call Shell(stAppName, 1)
set cancel property to true
Ex: button1.cancel = true
Most of the visual basic applications are available on 32 bit Intel platforms. These applications also run on many of the windows software systems such as server 2003, XP, Vista, etc.
setabort and setcomplete
Userforms should be used for complex user input. When an application input has non text as an input it is advisable to use Userforms rather than the input boxes. When you are using Userforms a user can give input any number of times which is not the case when you use input boxes. This can be accessible from the insert menu in your VBA editor after which you can insert your code.
Microsoft Visual basic has its host of problems one such being macros, Macros can be created which can create a havoc for a programmer with good intentions. Also the security issue rests in the hands of the user and not the programmer as such. A user can manipulate the VBA document.
1. Datagrid is Editable, flexgrid is Diplay only.
2. DBGrid allows full data binding while MSFlexGrid allows read-only binding
3. MSFlex grid is smaller and allows cell merging while Datagrid is larger and does not allow cell merging
when we initialize the form at that time if we want to set any variable's value then we can set it by defining in constructor. constructor 's name always same as class name.and destructor is used to recover memory occupied by any variable defining in constructor.
constructor and destructor is the new way in object oriented languages to initialize the varibles at the time of object creation.
when we declare an object,we can pass the values to it,and that values will be assigned to the data members of that class,whose object it is.
a class can have no. of objects and no. of constructors. an constructor is called automatically when an object is created.
there is only one destructor in any class,that is to deallocated the memory of the object when an object is destroyed or no longer exist
Microsoft holds license for Visual basic applications and it has been developing that language. Visual basic applications have an embedded programming environment which assists programmers in developing custom solutions by using almost all features of visual basic. Applications which are currently hosting visual basic can fully utilize the power of Visual basic applications because they have an added functionality and ease of visual basic applications.
VBA is licensed to Microsoft and this compatible with and only Microsoft products. Code written is compiled by an intermediate language called P-code and this is stored in hosting applications such as Excel, Word and Access. The intermediate code is interpreted by a virtual machine. This code and intermediate language is the exclusive right of Microsoft.
A computer registry can be used to store configuration settings and application initialization. We can use Getsetting function to read registry settings and save settings function to write registry settings. Application name, section, key, setting, and default are to be specified for registry modifying. It is advisable to know about your computer settings before modifying registry settings.
Name property cannot set at run time
Shell command present in VBA can be used to start the dialer present in windows operating system. Phone number can be used to connect to your modem. With the use of shell and sendkeys you can dial to your user. Shell starts windows application and sendkeys inform the window to dial according to the keystrokes of the application. A macro can be used to start the cardfile program which activates the auto dialer feature.
No compatibility - creates new GUIDproject compatibility binary compatibility - maintains the references
Visual basic can be used within almost all Microsoft products such as Map point, Visio, Auto cad, Word perfect, ArcGIS, word, excel, etc. With VBA you can control many functions such as host application, menus, toolbars, user interface, import and export of files, data transfer and extraction from multiple interfaces.
VB do supports oops.
Polymorphism - Yes , Encapsulation -Yes, Inheritance - NO
To register component use
run command prompt type:
c: regsvr32 nameofcomp
For Activex DLL use:
For Activex Exe use:
COM add-ins are software program`s which are integrated into an application and they add already built in features to an existing application. They have common architecture across multiple applications which help in deploying applications much faster across varied applications. Microsoft 2007 supports various COM add-INS
The reasons which made Microsoft drop its support to VBA are as follows, Microsoft visual basic relies heavily on machine code which was written for Power PC architecture. Also it would take another two years for developing VBA support for its architecture. It also states that Microsoft will incorporate VBA in the next script of office release for Mac.
Advantages of ActiveX Dll
1) An in-process component shares its client?s address space, so property and method calls don?t have to be marshaled. This results in much faster performance.
Disadvantages of ActiveX Dll
1) If an unhandled error occurs it will cause the client process to stop operating.
Advantages of ActiveX Exe
1) The component can run as a standalone desktop application, like Microsoft Excel or Microsoft Word, in addition to providing objects.
2) The component can process requests on an independent thread of execution, notifying the client of task completion using events or asynchronous call-backs. This frees the client to respond to the user.
3)If an error occurs the client processes can continue to operate.
Disadvantages of ActiveX Exe
1) Generally slower than an ActiveX dll alternative.
Benefit of wrapping database calls into MTS transa...
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.
Type libraries are files that explicitly describe some or all of the contents of components. This includes information about the methods, properties, constants, and other members exposed by the component. Development tools such as Visual Basic make use of the information contained in the type library to help you, as a developer, access and use the component. In addition, type libraries provide a convenient way to include a simple level of descriptive documentation for component members.
If you pass an argument by reference when calling a procedure, the procedure access to the actual variable in memory. As a result, the variable's value can be changed by the procedure.
If you pass an argument by value when calling a procedure, the variable's value can be changed with in the procedure only outside the actual value of the variable is retained.
Passing by reference is the default in VBA. If you do not explicitly specify to pass an argurment by value, VBA will pass it by reference.
Argument Passing ByVal
Describes passing arguments by value, which means the procedure cannot modify the variable itself.
Argument Passing ByRef
Describes passing arguments by reference, which means the procedure can modify the variable itself.
Option Explicit makes the declaration of Variables Mandatory
Data validation is an important concept in VBA. Application procedure and a custom dialog box can be used to correct input errors. You can assign an application procedure to the frame of a dialog box. Error message or custom dialog box can be highlighted with the first field with errors.
Line explicit function makes the compiler to identify all the variables which are not specified by the dim statement. This command significantly reduces the problem of type errors. This is used extensively because VBA deals with information rich applications in which type errors are common.
Visual basic applications have very rich and flexible applications but there is one limitation when using pointer function. Windows API has limited support for function pointers because it has the ability to use but not the functional support to call back the function. But later versions have support for modules. Function pointers have inbuilt support (DLL`s) for call but not for call back.
Datagrid,listbox,combobox,label,button have refresh methodand textbox has clear methodalmost all controls have refresh method
Cursor types:1. Forwardonly, 2. Static, 3. Keyset 4. Dyanmic
Lock types : 1. lockpessimistic, 2. lockoptimistic,3. lockbatchoptimistic 4. lockreadonly
The chief use of VBA is to make use of its special function which helps in repeated actions. Goal seek function helps to reduce manual entry of the code each and every time. This solves the problem of repeated function entry by automating functions and actions. Sub routines are inserted into the using the VBA editor and command insert module.
Format functions can be used to format many of the expressions such as currency, time, date, percentages and numbers. These functions are much simpler to use in VBA. User defined date, numeric and string formats are present in many of the applications.
Visual basic is useful if you are planning to develop your programs from scratch. This language helps you in developing Active x controls, exe files, etc.
Visual script is a powerful tool, through which you can create small scale applications on web pages, automation applications, etc. Integrated development environment is not present for VB script.
Visual basic applications are very useful in automating your existing application. VB application is useful for developing already existing applications.
The Controls which do not have Align property can't be placed on MDI Form.
E.g., Picturebox only has Align property in Standard Components of VB other controls dont have align property an hence can't be drawn on MDI Form.
Timer control can also be placed on MDI form.
MsgBox is a built in VB function which displays a Message Box and MsgBoxQ is a function defined by the user.
The ADO objects are:
Connection: Used to make a connection between your app and an external data source, i.e., sql server. Command: Used to build queries, including user-specific parameters, to access records from a data source (which are returned in a Recordset) Recordset: Used to access records returned from an SQL query. With a recordset, you can navigate returned records. You can also add, modify or delete records.