Visual Basic Controls

Working with Visual Basic Controls:

Visual Basic offers a set of controls which are placed in the toolbox.  The additional set of components is provided in the component list. 

The property and the methods of these classes can be access through the object using dot operator

E.g Command1.caption=”Hello”

1. Text Box:The text box control is the most commonly used to get the input from the user.  The text property of the textbox can be used to access the content of the textbox control

Text Box

Properties of Text Box:

·    Enabled: Set whether the user is allowed to access the control or not.  If set to false the textbox is disabled.

 

·    Locked: If we set to true that text box will not allow the user to get the content of the text box.  Unlike the enable property if will allow to copy and paste the control of the textbox.

 

·    Maxlength:  Set the maximum length of the characters that can be entered.

 

·    Multiline:  When the text exceeds the boundaries of the control the text will be wrapping to the next line if the multiline property is set to true.

 

·    Passwordchar:  The character to be displayed should be entered here to hide the text from the user.

 

·  Text: The text entered in the textbox limited to 2048 characters.  If the multiline property is set to true then it is 32 KB.

 

·   Visible: Set whether the control is hidden or visible. Setting if false hides the control.

2. Command Button: Command button is a three dimensional rectangular button, when the user clicks the button at run time VB invokes the code given in the click event.

Most visual basic applications have command buttons that allow the user to simply click them to perform action.

Properties of Command Button:

    ·      Backcolor: Set the background color only if the style property is set to graphics (1)

 

    ·     Caption:  Set the text display on the button.

 

    ·    Cancel:  When this property is set to true then the button can be click using escape             key.

    ·    Picture:  Set the picture is display on the button if the style property of the button is set      to graphics

3. List Box:  List box control display the list of items from which the user can select one or more. If the number of item exceeds the number that can be displayed, scroll bar is automatically added to list box control.  By default the choices are displayed in the vertical columns although multiple columns can be set.

List Box

Adding Items: You can add items in two ways that is design time and runtime.

 

Design Time: At a design time by setting the list property of the property window of the list box control.

 

Run Time:  You can add the item in the list box at runtime by using following code

 

Private command1_click()

List1.Additem ”Wardha”

End Sub

 

Removing Items:

 

List1.RemoveItem 0

Remove item has one argument, index, which specifies the item to remove

 

To remove the currently selected item from the list

Privates of command1_Click()

List1.RemoveItem Lis1.ListIndex

End Sub

 Clear method

 To remove all the items from the listbox the clear method is used.

 List1. Clear

 

  Listcount property:

  List count property returns the number of item in the list box

  Privates of command1_Click()

  msgbox(“The number of Items in the List1”& List1.ListCount)

End Sub

 4. Combo Box:  A combo box control combines the features of 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.

 

Combo box presents a list of choices to the user. If the number of items exceeds what can be displayed in the combo box, the scrollbar will automatically appear on the control. The user can then scroll up and down or left to right through the list.

Combo Box

Unlike list box control, the user can select only one item at a time from the combo box.

The properties and methods of the combo box control is very much similar to list box.

 Combo Box control Vs List Box control

Although both the combo box and list box control offers the list of options there are few differences between them.

1.    In combo box control the user can type text while the text cannot be typed into the list box control

2.    User can select only one option at a time from the list of available option,  while in case of the list box control the user can select the multiple options at a time

     3.    The list of items are displayed only in single column in the combo box control,  while the items can be displayed in multiple columns in list box control.

5. Picture box: The picture box control is used to display the graphics, to act as a container for the other control, and text using print method

Picture box control is similar to image control; each can be used to display graphics in your application. Each supports the same graphics format.

 

Picture property: Picture property of the picture box control can be used to set the picture in the picture box control. The picture property of the picture box control can be set at design time as well as run time

 

Loadpicture() method : The Loadpicture()can be used to display the picture into the picture box control at the runtime.

 

The path of the image to be loaded is passed as an argument to the Loadpicture() method

Picture Box

Private Sub Command1_Click()

Picture1.Picture= Loadpicture(“C:\ uranus.jpg”)

End Sub 

Graphics methods: Picture boxes, like forms, can be used to receive the output of the graphics method such a Circle, Line and Point.

 

 To draw a line in the picture box control, the line method is used.

 

Picture1.Line(x1,y1)-(x2, y2)

 

Where x1, y1 are the coordinates of the starting point of the line and x2, y2 are the coordinates of the end point of the line.

Syntax for circle method:

 

Circle(x,y),r

 

Private Sub-Command1_Click()

Picture1.Line(10,10)-(1000, 1000)

Circle( 1200,1000),750

End Sub

6. Image Control:The image control can be used to display the images on the form. It supports the same picture format as that of picture box control.

Picture property:  The picture property of the image control is used to load the pictures at design time

Private Sub Command1_click()

Image1.Picture= Loadpicture(“C:\apple.jpg”)

End Sub 

    Stretch property: The stretch property determine whether the picture is stretch when               loaded, to the size of the image control at the design time.

    Stretching the picture can be produced the loss of the image quality 

7.   Option Button: An option button control displays an option that can be turned on or off. 

Option buttons are also called as a radio button since you can tune into only one channel at a time. Usually option button controls are used in an option group to display options from which the user can select only one.

Option button control can be grouped by drawing them inside a container such as frame control.

The value property of the option button control can be used to identify whether the option button is currently selected or not.  If the option button is currently selected then its value property is true otherwise it is false.

Option Button

Private Sub Command1_click()

If Option1.value= True then 

Msgbox “Male”

Else

Msgbox “Female”

End If 

End Sub 

8. Checkbox:  The checkbox control officer list of choices from which the user can select as many options as required.  Checkbox control displays checkmarks when it is selected.  It is commonly used to present Yes/No or True/ False selection to the user.

Value property:  The value property of the checkbox control indicates whether the checkbox is checked or unchecked.

When the checkbox is selected the value is set to 1 otherwise it is 0.

Private Sub Command1_click()

If Check1. Value=1 Then

Text1.FontBold= True

ElseIf Check1.Value=0 Then

Text1.FontBold= False

End If 

 

If Check2. Value=1 Then

Text1.FontItalic= True

ElseIf Check2.Value=0 Then

Text1.FontItalic= False

End If 

 

If Check3. Value=1 Then

Text1.FontUnderline= True

ElseIf Check3.Value=0 Then

Text1.FontUnderline= False

End If 

End Sub 

Check Box 

9. Scrollbar: Scrollbar control is a visual basic control containing a thumb, you can move the scrollbar by dragging it, clicking the mouse to either side of the scrollbar, are using the keyboard.

Scrollbar control are useful when you want to select a discrete value or for a set of only creative values in a range.

When become of the scrollbar is moved, the current value of the scrollbar is changed.

There are two type of scroll bar available in toolbox:

1. Horizontal scroll bar
2.  Vertical scroll bar

 Properties:

 

1. Max Property:  Set the maximum value of the thumb of the scrollbar reaches its extreme right
2. Min property : Set the minimum value Hindi thumb of the scrollbar reaches its extreme left
3. Smallchange property:  Set the amount of increase or decrease in the value if the user Clicks on the arrow pointing to the left or right
4. Value property:  It is the value corresponding to the position of the scroll box in the scroll bar
5. Change event:  The change event of the scrollbar is executed as the current value of the scrollbar is changed.  The scrollbar value is changed when the scroll bar thumb is more either left or right.

HScroll & VScroll

Private Sub Hscroll1_Change()

Text1.text= Hscroll1.Value

End Sub

Private Sub Vscroll1_Change()

Text2.text= Vscroll1.Value

End Sub

Array of controls:

An array is defined as a group of elements of similar type. Similarly to an array of integers, single, string an array of control can be created.

All the control in the control array will share the same name

The individual element in the control array can be referred using an index which begins with 0.

To create an array

1. Place the control on the form
2. Copy the control
3. Past control

For example to create an Array of command buttons, place a command button on the form, copy and paste it.

The first button is now referred as a command1 (0), second one as command1 (1) and so on.

The code in the click event can be specified as,

Private Sub Command1_Click (index as integer) 

End Sub

The index of the button click is passed as an argument to the procedure.

 

Setting the background color of the form using three scroll bars

 

Place a horizontal scrollbar on the form, right click on the scroll bar and select copy and click on the paste.

 It creates the control array of the scrollbar on the form.  Again paste one more scrollbar on the form

 

The first scrollbar is identified as Hscroll1(0), Second scroll bar as Hscroll1(1)  while the third as Hscroll1(2).

Array of Control

Private Sub Hscroll1_Change (Index as integer)

Form1.Backcolor= RGB(Hscroll1(0).Value,Hscroll1(1).Value,Hscroll1(2).Value)

End Sub

10. Frame: Frame control can be used to group the control in it. It is commonly used to group the radio button as only one radio button can be selected from the individual group.

 Frame control provides an identifiable grouping of controls. You can also use a frame to subdivide a form functionally- for example separate group option buttons.

 To group controls, first draw the frame control and then draw the controls inside the frame. This enables you to move the frame and the control it contains together.  If you draw the control outside the frame and then try to move It Inside, The control will be on top of the frame and you will have to move the frame and control separately.

Frame

11. File Control:

Driver list box:  Drive list box control enables a user to select a valid disc drive at runtime.  Use this control to display a list of all the valid drivers in the user system

 

Directory list box:  A directory list box control display directories and path at runtime.  Use this control to display the hierarchical list of directories

 

File list box:  If file list box control locates and list file in the directory specified by the path property at runtime.  Use this control to display a list of files selected by file type 

Private Sub Form_Load()

Drive1.Drive=”C:\”

End Sub

Private Sub Drive1_Change()

Dir1.Path=Drive1.Drive

End Sub

Private Sub Dir1_Change()

File1.Path= Dir1.Path

End Sub

Drive List Box

Directory List

File List

Two- Way List & Its Operations

Two Way Lists:

Two way lists is a linear collection of data elements, called nodes, where each node N is divided into three parts:

1. An information field INFO which contains data of node N.
2. A pointer field FORW which contains the location of the next node in the list.
3. A pointer Field BACK which contain the location of the preceding node in the list

The list also requires a pointer variable: FIRST, which points to the first node in the list, and LAST, which points to the last node in the list shown in figure.  Observe that NULL pointer appears in FORW field of the last node in the list and also in BACK field of the first node in the list:

Observe that using the variable FIRST and the pointer field FORW, we can traverse into a list in forward direction.  On the other hand using the variable LAST and pointer variable BACK we can also traverse the list in backward direction 

Suppose LOCA and LOCB are the locations, respectively, of node A and B in a two way list.  Then the way that the pointer FORW and BACK are define given us the following:

Pointer property: FORW [LOCA] = LOCB if and only if BACK [LOCB]:=LOCA

Deleting a node in Two-Way List:

Suppose we are given the location LOC of node N in LIST and suppose you want to delete N from the list. N is deleted from the list by changing the following pair of pointers.

FORW[BACK[LOC]]:= FORW[LOC] and BACK[FORW[LOC]]:=BACK[LOC]

  The deleted N is then returned to AVAIL list by the assignment:

                     FORW [LOC]:=AVAIL             and      AVAIL:=LOC

Algorithm: DELTWL (INFO, FORW, BACK, START, AVAIL, LOC)

1. [Delete node.]

            Set FORW [BACK [LOC]]:= FORW[LOC] and 

                BACK [FORW [LOC]]:=BACK[LOC]

         2.  [Return node to AVAIL list]

            Set FORW[LOC]:=AVAIL and AVAIL:=LOC

     3. Exit

Inserting a node in Two-Way List:

Suppose we are given the location LOCA and LOCB of adjacent nodes A and B in the list, and suppose we want to insert a given ITEM of information between nodes A node B.  As with a one way list, first we remove the first node N from the AVAIL list,  using the variable new to keep track of its location,  and then we copy the data ITEM into the node N,  we set:

 NEW: = AVAIL,         AVAIL: =FORW[AVAIL],      INFO[NEW]:=ITEM

 Now the node N with the content ITEM is inserted into the list by changing the following pair of pointers: 

                FORW[LOCA]:=NEW ,                   FORW[NEW]:=LOCB

                BACK[LOCB]:=NEW ,                  BACK[NEW]:=LOCA

Algorithm: INSTWL (INFO, FORW, BACK, START, AVAIL, LOCA, LOCB, ITEM)

1. [OVERFLOW?] If AVAIL=NULL, then: Write: OVERFLOW, and Exit

2.[Remove the node from list and copy new data into node

        Set NEW:= AVAIL,   AVAIL:=FORW[AVAIL],       INFO[NEW]

3.[Insert node into list]

        Set FORW[LOCA]:=NEW ,             FORW[NEW]:=LOCB

  BACK[LOCB]:=NEW ,              BACK[NEW]:=LOCA 

Header Linked List & Polynomials

Header Linked List:

Header linked list is a linked list which always contains a special node, all the header nodes at the beginning of the list.

The following are the two kinds of widely used header lists:

1. A grounded header list is a header list where the last node contains null pointer.
2. A circular header list is a header list where last node points back to the header node

Observe that the list pointer start always points to the header node, accordingly LINK[START]=NULL indicates that the grounded release is empty.  And LINK[START]=START  indicates the circular header list is empty.

 Algorithm: (Traversing a circular header list) Let List be circular header list  in memory. This algorithm traverses list, applying an operation process to each node of list.

1. Set PTR:=LINK[START] [Initialize the pointer PTR]
2.  Repeat steps 3 and 4 while PTR!= START
3.  Apply process to INFO[PTR] 
4. Set PTR:=LINK[PTR]  [PTR now point to next node]

        [ End of step 2 loop]

    5. Exit

Polynomials:

Header linked list are frequently used to maintain the polynomials in memory.  The header list plays an important part of this representation. 

Let p(x) denotes the following polynomial in one variable (containing four non zero terms):

                                             p(x)=2x8-5x7-3x2+4

 Then p(x) may be represented by the header linked list shown in figure, where each node corresponds to a non zero term p(x).  Specifically, the information part of the nod is divided into two field representing, respectively, the coefficient and the exponent of the corresponding term, and in node or link according to decreasing degree.

 Observe that the list pointer variable POLY points to the header node, whose exponent field is assign in negative number, in this case - 1.  Here the array representation of the linked list will require three linear arrays, which will call COEF, EXP and LINK.

Deletion a node from One-Way List.

Deletion from a Linked List:

Let list be a linked list with node N between node A and B, shown in figure.  Suppose node N is to be deleted from the linked list.  The schematic diagram of such deletion appears in figure.  The deletion occurs as soon as the next pointer field of node A is changed so that it points to node B( accordingly, when performing deletion, one must keep track of the address of the node which immediately precedes  the node that is to be deleted)

 Suppose our linked list is maintained in memory in the form of

                                    LIST( INFO, LINK, START, AVAIL) 

When node N is deleted from our list, we will immediately return its memory space to the AVAIL list. Specifically, for easier processing, it will be returned to the beginning of the AVAIL list.

1. The next pointer field of node A now points to node B, where node N previously pointed.
2. The next pointer field of N now points to the original of first node in the free pool, where the AVAIL previously pointed.
3.  The AVAIL now points to the deleted node N

Deletion algorithm:

Algorithms which delete nodes from linked list come up with various situations. The first one deletes the node following a given node, and the second one deletes the node with a given item of information.  Our entire algorithm assumes that the linked list is in memory in the form of LIST (INFO, LINK, START, AVAIL).

 All of our deletion algorithm will return the memory space of the deleted node and to the beginning of the AVAIL list. Accordingly,  all of our algorithm will include the following pair of assignment, where LOC is the location of the deleted node N

                                    LINK[LOC]:=AVAIL and AVAIL:=LOC

Deleting a node following a given node

Let LIST be a linked list in memory. Suppose we are given the location LOC of the node N in the list.  Furthermore, suppose we are given the location LOCP of the node preceding N or, when n is the first node, we are given LOCP=NULL 

Algorithm: DEL(INFO, LINK, START, AVAIL, LOC, LOCP)

This algorithm deletes the node N with the location LOC. LOCP is the location of the node which precedes N, or when N is the, LOCP=NULL.

1. If LOCP= NULL, then:

            Set START:=LINK[START]  [Delete first node]

        Else

            Set LINK[LOCP]:=LINK[LOC] [Delete node N]

    [End of If structure]

    2. [Return the deleted node to the AVAIL list]

            Set LINK[LOC]:= AVAIL and AVAIL:=LOC

               3.    Exit.