SEE5A/ Visual Basic Unit : I - V

Transcription

1 SEE5A/ Visual Basic Unit : I - V 1 1

2 UNIT I : Syllabus Customizing a Form Writing Simple Programs Tool Box Creating Controls Name Property Command Button, Access Keys Image Controls, Text Boxes, Labels Message Boxes Grid, Editing Tools Variables, Data types, String Numbers 1 2

3 UNIT I : Syllabus Visual Basic provides GUI and provides facilities like text boxes, command buttons, list boxes, scroll bars, grids etc. The latest version of VB is VB

4 What is visual Basic? Visual Basic is a tool that allows you to develop Windows (Graphic User Interface - GUI) applications. The applications have a familiar appearance to the user. Visual Basic is event-driven, meaning code remains idle until called upon to respond to some event (button pressing, menu selection,...). Visual Basic is governed by an event processor. Nothing happens until an event is detected. Once an event is detected, the code corresponding to that event (event procedure) is executed. Program control is then returned to the event processor 1 4

5 Modes of VB Visual Basic operates in three modes: Design mode - used to build application Run mode - used to run the application Break mode - application halted and debugger is available Customizing the form Six windows appear when you start Visual Basic The Main Window consists of the title bar, menu bar, and toolbar 1 5

6 Customizing the form The Form Window is central to developing Visual Basic applications. It is where you draw your application. The Toolbox is the selection menu for controls used in your application. 1 6

7 Customizing the form The Properties Window is used to establish initial property values for objects. The drop-down box at the top of the window lists all objects in the current form. The Form Layout Window shows where (upon program execution)your form will be displayed relative to your monitor s screen 1 7

8 Customizing the form The Project Window displays a list of all forms and modules making up your application. You can also obtain a view of the Form or Code windows (window containing the actual Basic coding) from the Project window. How to create use a User control in VB 1 8

9 Name Property The Name property is a string used by clients to identify, find, or announce an object for the user. All objects support the Name property. For example, the text on a button control is its name, while the name for a list box or edit control is the static text that immediately precedes the control in the tabbing order. Command button The command button control is used to begin, interrupt, or end a process. When clicked, it invokes a command that has been written into its Click event procedure. Most Visual Basic applications have command buttons that allow the user to simply click them to perform actions. 1 9

10 Access Key An access key is an underlined character in the text of a menu, menu item, or the label of a control such as a button. With an access key, the user can "click" a button by pressing the ALT key in combination with the predefined access key. Command button The command button control is used to begin, interrupt, or end a process. When clicked, it invokes a command that has been written into its Click event procedure. Most Visual Basic applications have command buttons that allow the user to simply click them to perform actions. 1 10

11 Picture Box as a Container. The Visual Basic 6.0 PictureBox control is a container control; in addition to displaying pictures it can be used to group and display other controls. The Text Box control in Visual Basic 6.0 is replaced by the Windows Forms Text Box control in Visual Basic The names of some properties, methods, events, and constants are different, and in some cases there are differences in behavior. 1 11

12 A label is a graphical control element which displays text on a form. It is usually a static control; having no interactivity.... Unlike a standard label, a link label looks and acts like a hyperlink, and can be selected and activated. This control may have features such as changing colour when clicked or hovered over. Editing tools in vb Grid Control 1 12

13 Variable Local and Member Variables. A local variable is one that is declared within a procedure. A member variable is a member of a Visual Basic type; it is declared at module level, inside a class, structure, or module, but not within any procedure internal to that class, structure, or module. Datatype Variables are placeholders used to store values; they have names and data types. The data type of a variable determines how the bits representing those values are stored in the computer's memory. When you declare a variable, you can also supply a data type for it. Dim was only used to declare arrays. 1 13

14 Working with Message Box in VB String numbers in VB 1 14

15 Important Questions: What is Variable? Define Datatypes with example. Explain about the IDE. What is meant by Grid control. What is Activex control. 1 15

16 UNIT II : Syllabus Displaying Information Determinate Loops Indeterminate Loops Conditionals Built-in Functions Functions and Procedures 1 16

17 Displaying information The Appearance of Forms The main characteristic of a Form is the title bar on which the Form's caption is displayed. On the left end of the title bar is the Control Menu icon. Clicking this icon opens the Control Menu. Maximize, Minimize and Close buttons can be found on the right side of the Form. 1 17

18 Loading and Unloading forms In order to load and unload the forms, Load and Unload statements are used. The Load statement has the following syntax : Load FormName And the Unload statement has the following syntax : Unload FormName Showing Forms Show method is used to Show a Form. If the Form is loaded but invisible, the Show method is used to bring the Form on Top every other window. If the Form is not loaded, the Show method loads it and then displays it. Syntax of the Show method of the Form FormName.Show mode 1 18

19 Hiding forms The Hide method is used to hide a Form. The following is the syntax of the Hide Method. FormName.Hide To hide a Form from within its own code, the following code can be used. Me.Hide Displaying information in Forms If the user wants to make form respond to mouse click, Double click any part of form1. Double click opens code window 1 19

20 Loops All loops have two parts: The body of the loop (the statements being repeated) a termination condition that stops the loop Failure to have a valid termination condition can lead to an endless loop Types of Loops Event-driven Determinate Indeterminate Event-driven loops are repeated by the user causing an event to occur Determinate loops repeat a known number of times Indeterminate loops repeat an unknown number of times Variables should be initialized before being used in a loop 1 20

21 Event Driven loop Event-driven loops are repeated by user causing an event to occur Variable scope is important for loops; Variables in event procedures are local and are reset to zero when procedure terminates Variables defined at form level are known to all procedures and retain their value between events Form-level variables are declared in the Declarations procedure of the General object Static variables retain their value between events but are local to event procedure Declared with Static keyword 1 21

22 Determinate Loop For Next Loop Best way to create a determinate loop is to use a For-Next Loop For variable = start value to end value Step change value statements that compose body of loop Next variable where variable = the counter variable in the loop start value = the beginning value of the counter variable end value = the ending value of the counter variable change value = the amount the counter variable changes each time through the loop Next variable = the end of the For loop 1 22

23 Indeterminate Loop Indeterminate loops run for an unknown number of repetitions until a condition is true or while a condition is true Pre-Test loops have termination condition before loop body Post-test loops have termination condition after loop body While Wend Syntax: While (expression). body of the loop.... Wend While Wend Do while loop Do Until Loop Do While Syntax: Do while (expression) body of the loop.. Loop Do Until loop Syntax : Do until ( expression)......body of the loop... Loop 1 23

24 Control structure If then else For two alternative decisions, the If-Then-Else decision structure should be used In pseudocode, this is: If condition is true then implement true alternative Else implement false alternative End Decision Multiple alternative For multiple alternatives, the general form in pseudocode is: Select one: Condition 1 is true; implement alternative 1 Condition 2 is true: implement alternative 2 Condition 3 is true; implement alternative 3 End Selection. 24

25 Built in Function Many built-in functions are offered by Visual Basic fall under various categories. These functions are procedures that return a value. Basic Categories: o Date and Time Functions o Format Function o String Function 1 25

26 Built in Function 26

27 Procedure and sub functions 1 27

28 Procedure and sub functions 1 28

29 Procedure and sub functions 1 29

30 Important Questions: What is loops? Difference between determinate and indeterminate loop Explain about the If condition statement with example. What is switch case Explain detail about the functions and procedure in vb. Define built in functions 1 30

31 UNIT III : Syllabus Lists Arrays Sorting and Searching Records Control Arrays Combo Boxes Grid Control Projects with Multiple forms Do Events and Sub Main Error Trapping. 1 31

32 Lists In VB.Net applications both lists and dictionaries are used to store collections of data. List (Collection ) is simply a set of items and Dictionary(Dictionary) is a set of key-value pairs. The essential difference therefore is in how the containers are indexed data in your VB.Net application. List is a generic implementation of ArrayList. List can store only one type of objects, that type supplied as its generic parameter. List class is a collection and defined in the System. Collection, Generic namespace and it provides the methods and properties like other Collection classes such as add, insert, remove, search etc. 1 32

33 Arrays An array is a consecutive group of memory locations that all have the same name and the same type. To refer to a particular location or element in the array, we specify the array name and the array element position number. The Individual elements of an array are identified using an index. Arrays have upper and lower bounds and the elements have to lie within those bounds. Each index number in an array is allocated individual memory space and therefore users must be declaring arrays of larger size than required. 1 33

34 Arrays Declaration of Array Arrays occupy space in memory. The programmer specifies the array type and the number of elements required by the array so that the compiler may reserve the appropriate amount of memory. Types of Array Fixed Array The size of array always remains the same-size doesn't change during the program execution. Dynamic Array The size of the array can be changed at the run time- size changes during the program execution 1 34

35 Sorting A sorting operation orders the elements of a sequence based on one or more attributes.... The following illustration shows the results of an alphabetical sort operation on a sequence of characters. The standard query operator methods that sort data are listed in the following section. Bubble Sort Selection sort Insertion sort Shell sort Heap sort Quick sort 1 35

36 Searching A searching operation search the element from the list. Binary search Linear search Records A table is an object that holds that information of database. 1 36

37 Control Array 1. A control array is group of the same type control which is assigned a single name. 2. The individual controls are identified by the control array name and an index value. 3. The Case decision structure can be useful in working with a control array. 4. To create a control array, just enter the same name for more than one control and reply yes to the query. 5. The order in which the controls are entered determines the index values for the controls in the control array. Example Simple calculator 1 37

38 Combo box The ComboBox is called that because it's a combination of a ListBox and a TextBox. It has the advantage over the ListBox of not taking up space until it is actually used which means that it makes it easier to position on the Form. But the combo has the disadvantage, sort of, that the user can enter his own information, in addition to what is in the list. This may make data validation harder because the choices are not limited. When you want to force the user to make a choice only among the specified items, use a ListBox, even if it is a bit more awkward. If the user is allowed to override the choices, uses a ComboBox. 1 38

39 Combo box As in the ListBox, use the Text property to get the information input. Label3.Caption = cbo_position.text 1 39

40 Grid Control The DataGrid control in Visual Basic 6.0 is replaced by the Windows Forms DataGridView control in Visual Basic The names of some properties, methods, events, and constants are different, and in some cases there are differences in behavior. Private Sub DataGrid1_Click() DataGrid1.SelStart = 1 DataGrid1.SelLength = DataGrid1.Text MsgBox("The selected text is " & DataGrid1.SelText) End Sub Data display mode in the window form Datagrid control Bound, Un bound, Virtual 1 40

41 Projects with Multiple form 1 41

42 Sub Main 1 42

43 Sub Main and DoEvents 1 43

44 Error Handling Error handling is essential to all professional applications. Any number of run-time errors can occur, and if your program does not trap them, the VB default action is to report the error and then terminate the program (often resulting in the end user calling you and complaining, "Your program kicked me out!"). The following statements are error handling: On Error GoTo label This form of the On Error statement redirects program execution to the line label specified. On Error Resume Next This form of the On Error statement tells VB to continue with the line of code following the line where the error occurred. With this type of error trap, you would normally test for an error at selected points in the program code where you anticipate that an error may occur. 1 44

45 Important Questions: What is Grid control?explain with example. Detail about the control array with example Define sub main and Do events procedure Difference between list box and combo box What is array? 1 45

46 UNIT IV : Syllabus VB Objects Dialog Boxes Common Controls Menus MDI forms Testing Debugging and optimization Working with graphics 1 46

47 VB Objects Visual Basic is object based language. Goto View Object Browser Press F2 and use tool bar short cut Object Browser gives complete access to the classes and objects and their methods and property. An object library contains the information that VB needs to build instances of its object. 1 47

48 Dialog Box Dialog Box in VB.NET. Dialog boxes are used to interact with the user and retrieve information. In simple terms, a dialog box is a form with its FormBorderStyle Enumeration property set to FixedDialog. You can construct your own custom dialog boxes using the Windows Forms Designer 1 48

49 Common controls The Common Dialog control provides a standard set of dialog boxes for operations such as opening, saving, and printing files, as well as selecting colors and fonts and displaying help. Goto Project Components Microsoft Common Dialog Box 6.0. Any six of the different dialog boxes can be displayed with just one Common Dialog control. ShowOpen, ShowSave, ShowPrinter, ShowColor, ShowFont, or ShowHelp 1 49

50 Common controls Image List Control List view Control Slider Control Status Bar Control Tab Strip Control Toolbar Control Tree View Control / 15

51 Menus Designing the right kind of menus will make our applications much more user-friendly. VB lets to build up to six levels of menus. Menus that kind submenus are usually called hierarchical menus. 1 51

52 Menu Editor To build the menu described above, perform the following steps. 1. Start a new VB project and invoke the Menu Editor using either method shown above (click the Menu Editor toolbar icon or select the Menu Editor option from the Tools menu). The Menu Editor screen appears, as shown below: 1 52

53 MDI Form MDI stands for multiple Document Interface. Here one window, usually called MDI container or MDI parent form.this contains many other windows, usually called Child Forms. 1 53

54 MDI Form - example In the below program, each time user clicks New from the file menu, a new child window is created and displayed. The following code is entered in the mnnew_click() procedure of the MDIForm1. Private Sub MnNew_click() Dim NewForm as new Form1 End sub. The following code is entered in mntile_click() procedure of the MDI form. Private Sub MnNew_click() Dim NewForm as new Form1 End sub. The following code is entered in mntile_click() procedure of the MDI form. 1 54

55 MDI Form - example Private submntile_click() MDIForm1.Arrange vbtilehorizontal End sub. The following code is entered in mncascade_click() procedure of the MDI form. Private sub mncascade_click() MDIForm1.Arrange vbcascade End sub. 1 55

56 Testing After writing programs it is necessary to test it for bugs.if we find errors in testing we need to eradicate them. Testing program: The first step in debugging is testing. One way of testing is to run the program few times to see what happens each time using slightly different input. This holds good for short program but it is not convincing for long program. Testing programs is an art, not a science. Since errors are often caused by bugs, error trapping can help to isolate portion of a procedure caused that caused the bug. Having an active error trap(on Error Goto) can prevent our test from doing their job. To temporarily disable any active error traps before starting the testing process we need to set Break on All Errors to on. 1 56

57 Stub programming In this type of programming we substitute constants whenever necessary, to find results. Define sub, Function or property that will eventually need, fill them with constants instead of having them do anything. In simple terms it is just skeletons where appropriate function, sub procedure can be added. Bugs: Bugs are generally errors. BUGS GRAMMATICAL LOGICAL 1 57

58 Debugging and optimization Choose View Toolbars Debug The debugging tools are used when the program is temporarily suspended( in break mode). The below diagram represents debugging tools in the order in which they appear on the tool bar. 1 58

59 Graphics Various controls and methods are used in Visual Basic to draw points, lines, boxes, circles and other shapes and their location and appearance on a Form can be changed. All visual basic movements, sizing and graphical drawing statements use a limit of one twip A twip is a unit that specifies the dimensions and locations of the graphics objects. There are 1440 twips in one inch. These measurements designate the object s size when printed. The RGB() function enables to specify colors. RGB stands for Red, Green and Blue.The maximum value of each argument is 255 and minimum is

60 Important Questions What is MDI? Explain in detail. Define menu editor. What is stub programming. Explain common controls in VB. Explain common dialog box. 1 60

61 UNIT IV : Syllabus Monitoring Mouse activity File Handling File System Controls File System Objects COM/OLE automation DLL Servers OLE Drag and Drop 1 61

62 Monitoring mouse activity Context-sensitive pop-up menus Tool tip pop up when the user holds the mouse over the control- using the ToolTip Property of the control. If a mouse button is pressed and held while the mouse pointer is inside a control or form that object captures the mouse Mouse Move That is no other Visual Basic object can react to mouse events until the user releases the mouse button, regardless of where the user moves the mouse Mouse control program - Example Mouse UP MOUSE EVENTS Mouse Down 1 62

63 File Handling File Commands Rename files Change the Logged Drive Switch Directories Copy files MkDir NewDir add a subdirectory called New Dir to the current Directory MkDir C:\NewDir add the subdirectory to the root directory of the C Drive ChDrive Changes the logged drive for the underlying operating system ChDir Changes the default directory MkDir Makes a new Directory RmDir Removes a directory Name Changes the name of the file or moves a file from one directory to another on the same drive Kill Deletes a file from a disk 1 63

64 Sequential files There may be too much information in the file, or you don t know what limits to use. Here is the way While there s information left in the file Get next piece of Info process it Loop We need a way to test when you are at the end of file. EOF(FileIdentifier) Do Until EOF(FileNum) Reading back character Common use of EOF statement is to read back the information contained in a file, character-by-character. StringvariableName =Input$(NumberOfChars, FileIdentifier) SixChar$ = Input$(6,#2) Pickup six character from file#2 opened for input and assigns them to a string variable named SixChar$ 1 64

65 File Handling Functions FileCopy Function FileDateTime Function The GetAttr Function The SetAttr function Rich textbox You can use some properties of the RichTextBox control to make it easy to send its contents to a file or to display the contents of a file inside of a RichTextBox control. LoadFile Method loads an.rtf file or text file into a RichTextBox control at one gulp. NameOfRichTextBox.LoadFile(Pathname,filetype) SaveFile Method saves the contents of a RichTextBox control to a file in one swoop. NameOfRichTextBox.SaveFile(Pathname,filetype) 1 65

66 File Handling Access Mode Input: open for sequential input; the file will be read sequentially starting at the beginning. Output: open for sequential output; records will be written sequentially starting at the beginning; if the file does not exist, it is created; if it does exist, it is overwritten. Random: open for random read and write; any specific record can be accessed. Append: sequential output to the end of an existing file; if the file does not exist it is created; it does not overwrite the file. Binary: open for binary read and write; access is at byte level. If access mode is not specified in the Open statement, For Random is used by default 1 66

67 File System Control File list boxes Directory list boxes Drive list boxes The file system Controls in VB allow users to select a new drive,see the hierarchical directory structure of a disk, or see the names of the files in a given directory. The file system controls are designed to work together. Code checks what the user has done to the drive list box and passes this information on to the directory list box. The changes in the directory list box are passed on to the file list box. 1 67

68 File System Objects File programming capabilities are supplied with VB6 as the Microsoft Scripting Runtime library of objects, in a file called SCRRUN.DLL. You will always need to add the reference to the scripting library You will always need to make a new FileSystemObject as your first step Once you have a new FileSystemObject, it has a Drives collection that tells you about the individual drives on the user machines The Drives collection can give you a Folders collection that tells you about the Folders on a drive. The Folders collection can have another Folders collection inside of if for its subfolders and a Files collection for the files in the folder You will have many ways of getting at individual drives, folders, or files and of reading off their properties. 1 68

69 OLE Automation Automation was designed with the ease of scripting in mind, so controllers often provide languages such as Visual Basic for Applications to end users, allowing them to control automation objects via scripts. Example to implement an Automation controller in VB6 for MS-Excel. The first thing we need to do after we have identified our objective and created a project is to add a reference to the Excel Object library. To accomplish this select Project References in Visual Basic 6 and check the Microsoft Excel 10.0 Object Library Building COM/OLE DLL Servers The basics of how you can turn a class module into a dynamic link library. DLL can be used the same way as libraries supplied for Excel or by a commercial vendor. New Project choose ActiveXDLL. Project Explorer adds the class module automatically. 1 69

70 Property of DLL Private PublicNotCreatable MultiUse GlobalMultiUse Register ActiveX DLL Projects 1. First compile DLL by choosing File/Compile 2. Then, run a program called regsvr32 to register it on your machine The regsvr32 program can be found in the\tools\regutils directory Dynamic Link Library DLL Stands for "Dynamic Link Library." A DLL (.dll) file contains a library of functions and other information that can be accessed by a Windows program. When a program is launched, links to the necessary.dll files are created. 1 70

71 OLE Drag and Drop One type of drag-and-drop, sometimes referred to as traditional dragand-drop, is limited to dragging between controls in the same application. I covered traditional drag-and-drop. The second type, called OLE (for Object Linking and Embedding) dragand-drop, lets the user drag data between applications as well as within an application. OLE drag-and-drop works only with applications that support it. This is the case with most Microsoft applications and many programs from other vendors as well. If you attempt OLE drag-and-drop with an application that does not support it, the operation simply does not work. 1 71

72 OLE Data object class The DataObject class is at the heart of OLE drag-and-drop. When a drag-and-drop operation is started, the data that is being dragged is packaged in a DataObject object. When the item is dropped, this object is available to the target, which examines the DataObject to determine if the data it contains is in a format that the target can accept. If so, the data is accepted by the target. If you have Microsoft Office installed you can see OLE drag-and-drop in action by starting Word and Excel, selecting some text in Word, and dragging it to Excel. The text appears in the Excel worksheet cell where it was dropped. You can use OLE drag-and-drop with more complex kind of data as well, such as charts and images. Traditionally, the drag-and-drop operation moves the data or, if the Ctrl key is depressed, copies the data 1 72

73 OLE Drag and Drop Only a subset of VB controls support OLE drag-and-drop. Those that can act as a source as well as a target are: ComboBox DirListBox FileListBox Image ListBox PictureBox TextBox How OLE Drag and Drop work in VB 1 73

74 OLE Drag and Drop The following components are limited to serving as a target: CheckBox CommandButton Data Form Frame Label MDIForm OptionButton PropertyPage UserControl UserDocument 1 74

75 Important Question and Answer Define OLE drag and drop What is DLL server Explain about the file handling functions. What is meant by OLE/COM 1 75