Visual basic bt0082
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The document discusses various concepts in Visual Basic such as extracting and drawing images using image list controls, inheritance, the Exit Try statement, SQL select statements, record navigation in datasets, and jagged arrays. It provides examples to explain each concept. For image list controls, it shows how to extract individual images and assign them to other controls, as well as how to draw images. For inheritance, it discusses the "is a" relationship between classes. The Exit Try statement example breaks out of a Try/Catch block. SQL select statements are demonstrated by selecting all records or specific columns. Record navigation in a dataset involves moving between records using previous/next buttons or going to the first/last record. Finally, jagged arrays
![Drawing Images
List Image objects support the Draw method, which has the following syntax:
Draw hDC, [x],[y],[Style]
Where hDC is the handle of a device context(typically the value returned by
the hDC property of a form, a PictureBox control, or the Printer object) and x
and y are the coordinates in pixel where the image should be displayed in the
target object. Style is one of the following values: 0-imlNormal(default, draw
the image without any change), 1-imlTransparent (use the Maskcolor property
to account for transparent areas), 2-imlSelected (draw the image diethered
with the system highlight color), or 3-imlFocus (as imlSelected, but create a
hatched effect to indicate that the image has the focus):
‘Show an image in the upper left corner of a PictureBox control.
ImageList1.ListImage(“Cut”).Draw Picture1.hDC,0,0
2. Explain the concept of inheritance in VB.Net.
Answer: Inheritanceis a powerful tool that saves you a lot of work if you use it
correctly. ”Correctly” means that you should not use inheritance if it is not
absolutely clear that the “is a” relationship holds:
Class A should inherit from a class B only when it is absolutely clear that,
now and forever, you can always use an A object in place of B object
without getting yourself into a trouble.
You may see this fundamental rule in a more abstract form. This kind of
abstraction is necessary when you try to express the rule in a code oriented way:
An instance of a child class A that inherits from a parent class B must be
usable in every piece of code that would take an instance of its parent
type as a parameter. In other words if you have a function whose
header is
Uselt(b Thing As B)](https://image.slidesharecdn.com/visualbasic-bt0082-160912171548/85/Visual-basic-bt0082-2-320.jpg)
Visual basic bt0082
- 1. Subject Code and Name: BT0082 and Visual Basic Roll No: 1408005884 1. Explain the process of extracting and drawing images using image list control. Answer: Extracting Individual Images A picture property can be exposed by each list image object. This makes you to extract the image and assign it to other control object, which can be a Picture Box or an Image control: Set Picture1.Picture = ImageList1.ListImage(“Cut”).Picture Picture property of a List Image Object can be used anywhere required. The example shows how a Picture property of a Picture Box is used: ‘Save an Image to a disk file. Save Picture ImageList1.ListImages(“Cut”).Picture,”C:cut.bmp” ‘Display an image on the current form, zooming it by a factor ‘of 4 along the X-axis, and 8 along the Y-axis With ImageList1 PaintPicture.ListImages(“Cut”).Picture,0,0,ScaleX(.Imagewidth,vbPixels)*4, _ScaleY(.ImageHeight,vbPixels) List Imageobjects also exposean Extraction method, which creates an icon out of the image and returns it to the earlier. You can therefore use this method whenever an icon is expected, as in this code: Form1.MouseIcon = ImageList1.ListImages(“Pointer”).Extraction
- 2. Drawing Images List Image objects support the Draw method, which has the following syntax: Draw hDC, [x],[y],[Style] Where hDC is the handle of a device context(typically the value returned by the hDC property of a form, a PictureBox control, or the Printer object) and x and y are the coordinates in pixel where the image should be displayed in the target object. Style is one of the following values: 0-imlNormal(default, draw the image without any change), 1-imlTransparent (use the Maskcolor property to account for transparent areas), 2-imlSelected (draw the image diethered with the system highlight color), or 3-imlFocus (as imlSelected, but create a hatched effect to indicate that the image has the focus): ‘Show an image in the upper left corner of a PictureBox control. ImageList1.ListImage(“Cut”).Draw Picture1.hDC,0,0 2. Explain the concept of inheritance in VB.Net. Answer: Inheritanceis a powerful tool that saves you a lot of work if you use it correctly. ”Correctly” means that you should not use inheritance if it is not absolutely clear that the “is a” relationship holds: Class A should inherit from a class B only when it is absolutely clear that, now and forever, you can always use an A object in place of B object without getting yourself into a trouble. You may see this fundamental rule in a more abstract form. This kind of abstraction is necessary when you try to express the rule in a code oriented way: An instance of a child class A that inherits from a parent class B must be usable in every piece of code that would take an instance of its parent type as a parameter. In other words if you have a function whose header is Uselt(b Thing As B)
- 3. And a Thing is an instance of the child class A, then the following code must make sense: Uselt(a Thing) 3. Explain the concept of Exit Try statement in VB.Net with an example. Answer: The Exit Try statement break out of the Try or Catch block and continue at the Finally block. Example: Private Function GetAverage5 (items As Integer, iTotal as Integer) As Single ‘Code that might throw an exception is wrapped in a Try block. Try Dim sngAverage = CSng(I Total/Items) ‘This only executes if the line above generated no error. MessageBox.Show(“Calculation successful”) Return sngAverage Cactch excDivideByZero As DivideByZeroException ‘You will gwt here with an DivideByzeroException in the Try block. If items = 0Then Return 0 Exit Try Else MessagezBox.Show(“Error not caused by items”) End If
- 4. Throw excDivideByZero MessageBox.Show(“More logic after the thrown – never executed”) Catch excGeneric As Exception ‘You,ll get here when any exception is thrown and not caught in ‘ a previous Catch block. MessageBox.Show (“Calculation failed – generic exception caught”) Throw excGeneric Finally ‘Code in the Finally block will always run, even if ‘an exception was thrown in a Catch block. MessageBox.Show(“You always get here, with or without an error”) End Try End Sub In your first Catch block, you have inserted an If block so that you can exit the block given a certain condition. The Exit Try goes immediately to the Finally block and completes the processing there: If items=0 Then Return 0 Exit Try Else MessagerBox.Show(“Error not caused by items”) End If
- 5. 4. Define SQL. Explain the select statement of SQL with examples. Answer: SQL (Structured Query Language) is a language is used to access, delete, update and create databases. This is easy and simple to learn. To view all the data in a table, following query has to be written: SELECT*FROM Table Name; The language is not case sensitive. The abovestatement can also be written as: Select*from Table Name; The suggested protocol is to use UPPERCASE for the keywords. The above whole line reads: “SELECT all the records FROM the table called Table Name” Always it is not necessary to select all the records using ”*". If the table has two column fields first name and surname, you can specify the query statement: SELECT tblContacts.FirstName, tblContacts.SurName FROM tblContacts When this query is executed, the FirstName and SurName columns will be returned. If you are using the free 2005 Express edition, you might see DataSet with a wiggly line under it. This is because you need to set a reference to something called System.Xml.dll. To do that, click Project>Add Reference from the menu bar.
- 6. 5. Describe the concept of record navigation in VB.Net. Answer: Record Navigation: (i) Move Back One Record at a Time To scroll backwards through the dataset, we need to reduce the value of inc by 1. That is to go by one record we have to decrement inc by 1 from whatever the currentvalue it has. Oncethe code is finished, run the program. A message box should display when you click on the Previous button. This will happen even though no records have been loaded in text boxes. This happens due to the inc value is -1 when the form loads. When Next button is clicked, the value gets assigned to zero. If inc>0 Then Inc = inc-1 Navigate Records() ElseIf inc= -1 Then MsgBox(“No Records Yet”) ElseIf inc = 0 Then MsgBox(“First Record”) End If Now inc is checked whether it is equal to -1 using the new if statement. If it is not then displays a message. A message box with a message “”First Record ” is displayed. (ii) Moving to the Last Record in the DataSet To navigate to the last record of the DataSet, you should know the count of the records loaded into DataSet i.e., the MaxRows variable in the code. If inc<>MaxRows-1 Then
- 7. ` inc=MaxRows-1 NavigateRecords() End If Within the if statement , inc is set to MaxRows-1. Then NavigateRecords() subroutine is executed. (iii) Moving to the First Record in the DataSet We have to assign a value 0 to the inc counter. If inc<>0 Then Inc=0 NavigateRecords() EndIf This code is to be added to the btnFirst. 6. Describe the concept of jagged arrays in visual basic with an example. Answer: A consecutive group of memory locations having same name and type is said to be an array. The elements in the array are put within name and type is said to be an array. An array of which each element is itself an array is called array of arrays or a jagged array. Having array as elements is not the same thing as a multidimensional array, which has more than one index on a single array. Sometimes the data structure in your application is two-dimensional but not rectangular. For example, you might have an array of months, each element5s of which is an array of days. Since different months have different numbers of days, the elements do not forma rectangular two-dimensional array. In such a case, you can use a jagged array instead of a multidimensional array.
- 8. Example: The following example declares an array variable to hold an array of arrays with elements of the Double Data Type. Each element of the array sales is itself an array that represents a month. Each month array holds values for each day in that month. Dim sales()() As Double = New Double(11)(){} Dim month As Integer Dim days As Integer For month = 0 To 11 Days = DateTime.DaysInmonth(Year(Now), month +1) sales(month) = New Double(days-1){} Next month The New clause in the declaration of sales sets the array variable ro a 12- element array, each element of which is of type Double(), an array of Double elements. The For loop then determines how many days are in each month this year (Year(New)),and sets the corresponding element of sales to a Double array of the appropriate size. The jagged array saves seven elements as compared to a two dimensional array. When you initialize a jagged array variable, you van specify the dimension lengths only for the top-level array.