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Visual basic asp.net programming introduction

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After starting the project and generating the code behind file, we learn a little on
OOP (Object Oriented Programming)
Class and what a Class may contain
Inheritance
Namespace
Access Levels
Variables: valid and invalid variable naming
Data types: Integer, String, Boolean, Decimal
Decision making using IF … ElseIf … Else … End If

Published in: Education
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Visual basic asp.net programming introduction

  1. 1. ASP.NET Visual Basic Web Form Introduction 1
  2. 2. What we will cover ● After starting the project and generating the code behind file, we learn a little on OOP (Object Oriented Programming) ○ Class and what a Class may contain ○ Inheritance ○ Namespace ○ Access Levels ● The very first subroutine - Page_Load, which execute every time the page is loaded. ● After that we move to Button_Click subroutine, which execute when button is clicked
  3. 3. What we will cover ● Variables: valid and invalid variable naming ● Data types: Integer, String, Boolean, Decimal ● Decision making using IF … ElseIf … Else … End If
  4. 4. Tool: Visual Studio 2012 or 2013 ● Download a FREE Visual Studio Express https://www.visualstudio.com/en-us/products/visual-studio-express-vs.aspx ● Launch Visual Studio and click on “New Project””.
  5. 5. DateAndTimeApp
  6. 6. New Web Form: PageLoad
  7. 7. New Web Form: PageLoad
  8. 8. Go to Code behind page ● Click anywhere outside the Div box to go to the “Code Behind”file:
  9. 9. PageLoad.aspx.vb Name of the auto-generated code behind file always same as the Web Form (PageLoad. aspx) and add “.vb” extension
  10. 10. Class and End Class Every Web Form is an Object. To define an object use “Class” and “End Class”
  11. 11. What does a Class contain? Eg: Label Class
  12. 12. What is Constructor When Label icon on the ToolBox is double click => to create a Label object on the page
  13. 13. What are Properties
  14. 14. What are Events
  15. 15. What are Methods Group of processing that we could ask the object to do
  16. 16. Inherits from parent class What do you get? You get for free “all” the parent’s constructor, properties, events and methods. So you just need to add new stuff.
  17. 17. Namespace (x.y.z) to prevent conflict Instead of just call it “Page”, Microsoft calls its Page class as “System.Web.UI.Page”. Someone else may provide another “Page” class but call theirs “Someone.Else.Page”. It is similar to a fullname of a person so as not to be mistaken.
  18. 18. Public, Protected, Private ● Public => anyone can use it ● Protected => Only those in the same Class can use it + children Class can use it too ● Private => Only those in the same Class can use it These are called Access levels..
  19. 19. Page_Load Subroutine Our Program to be added here. Will be executed every time the web form Page is Loaded!
  20. 20. Our first App When the application is run 1. a input will ask the users to key in their name. 2. another input will ask for their designation (Mr, Mrs, Ms, Miss). 3. Output a message: “Your name is xxxx, your designation is xx.”
  21. 21. Use libraries provided by Microsoft Before you reinvent the wheel and start to type code straight away, look for a suitable method from the libraries provided:
  22. 22. Variables ● A variable is a letter (eg x, y, z) or name (score, highScore, health) that can store a value. ● When you create computer programs, you can use variables to store numbers, such as the height of a building, or words, such as a person's name.
  23. 23. There are three steps to using a variable 1. Declare the variable: Tell the program the name and kind of variable you want to use. 2. Assign the variable: Give the variable a value to hold. 3. Use the variable: Retrieve the value held in the variable and use it in your program.
  24. 24. Declare ● When you declare a variable, you have to decide what to name it and what data type to assign to it. ● You can name the variable anything that you want, as long as the name starts with a letter or an underscore. The 2nd and subsequent characters may be letters or underscores or numbers,
  25. 25. Declare ● When you use a name that describes what the variable is holding, your code is easier to read. ● For example, a variable that tracks the number of pieces of candy in a jar could be named totalCandy.
  26. 26. Declare You declare a variable using the Dim and As keywords, as shown here. Dim aNumber As Integer Variable Type
  27. 27. Assign aNumber = 42
  28. 28. Declare and Assign Dim aNumber As Integer = 42
  29. 29. Avoid Keywords Avoid using keywords as variable Eg Dim, As, Integer, String, etc http://alturl.com/ix85i
  30. 30. Cannot include Space Variable name cannot contain SPACES or special characters such as !@#&-+.... Dim favourite fruit As String Use one of the following conventions for readability: favouriteFruit or favourite_fruit Cannot have space
  31. 31. Valid & Invalid variable names Valid i x _special_power a1 alien1 Invalid special power special-power 1alien reg#
  32. 32. Data Types http://alturl.com/6vg9j ● Boolean for true and false ● Decimal ● Integer ● String ● Date : :
  33. 33. Modify our app When the application is run 1. a input will ask the users to key in their age. 2. another input will ask for their height (in metre). 3. Output a message: “yy is your age and zz in metre is your height.”
  34. 34. Exercise: Try to do it on your own! When the application is run 1. a input will ask the users to key in their favourite fruit. 2. another input will ask for their weight (in kg). 3. yet another input to ask for their contact numbers. 4. Output a message: “Your favourite fruit is apple, your weight is 75kg and 9765235 is your contact number.”
  35. 35. Variables and Strings Summary
  36. 36. Names for variable Variable name cannot contain SPACES or special characters such as !@#&-+.... Dim favourite fruit As String Use one of the following conventions for readability: favouriteFruit or favourite_fruit Cannot have space
  37. 37. Valid & Invalid variable names Valid i x _special_power a1 alien1 Invalid special power special-power 1alien reg#
  38. 38. Declaration of Variables Dim fruit As String Dim weight As String Dim contact As String Dim output As String Instead of defining 4 string variables in separate lines, combine them into one by separating the variables with comma Dim fruit,weight,contact,output As String VS2012 will auto add space after comma!
  39. 39. Strings “This is a string” - anything from the start quotation to the end quotation is one string. Use & to combine two strings into one longer string: “An apple a day” & “keep doc away!” => “An apple a daykeep doc away!” How to have a space?
  40. 40. “An apple a day” & “ keep doc away!” => “An apple a day keep doc away!” “An apple a day ” & “keep doc away!” => “An apple a day keep doc away!” Add a space before k Add a space after y
  41. 41. “An ” & “apple a day ” & “keep doc away!” will combine the three strings into one longer string: “An apple a day keep doc away!”
  42. 42. Variables and Strings fruit = “apple” weight = “75” “I like ” & fruit & “ and my wt in kg is ” & weight
  43. 43. “I like ” & fruit & “ and my wt in kg is ” & weight will combine 4 strings into one longer string “I like apple and my wt in kg is 75”
  44. 44. output = “I like ” & fruit & “ and my wt in kg is ” & weight “I like apple and my wt in kg is 75” The combine string is assigned to output Step 1 Step 2
  45. 45. ASP.NET Visual Basic Web Form Introduction 2
  46. 46. Get Started Launch VS2012 New Project: DateAndTimeApp2 Add new item > Web Form: LoadPage2 Double click anywhere outside the “Div” box, to generate the *.vb code file.
  47. 47. First attempt When the application is run 1. Output a message: “Time now is xx:xx:xx AM”
  48. 48. Libraries provided by Microsoft Before you reinvent the wheel and start to type straight away, look for a suitable one from the libraries provided:
  49. 49. output = “Time now is ” & TimeOfDay “Time now is 09:15:36 AM” The combine string is assigned to output Step 1 Step 2
  50. 50. Modify App When the application is run 1. Ask user to key in a month from 1 to 12. Eg 1. 2. Output a message: “The month is January.” The month displayed will depends on the input of the user.
  51. 51. Parameters
  52. 52. Exercise: Try to do on your own! When the application is run 1. Ask user to key in a month from 1 to 12. Eg 5. 2. Output a message: “You have key in 5 and the month is May.” The number and month displayed will depends on the input of the user.
  53. 53. ASP.NET Visual Basic Web Form Introduction 3
  54. 54. Get Started Launch VS2012 New Project: GuessNumber Add new item > Web Form: BtnClick
  55. 55. Switch the web form to “Design View”. Then drag the various control from the Toolbox window. finally set their properties using the Properties Window.
  56. 56. Page Title Method 1: 1. Switch to source view. 2. Edit <title></title>. Method 2: In Properties window: 1. Select “DOCUMENT” from dropdown. 2. Add/modify “Title” property.
  57. 57. This App need to generate a random number for user to guess when the web page is loaded. The same number should remain till the game is over.
  58. 58. Get content from Web Control guess = txtAnswer.Text txtAnswer.Text property
  59. 59. Set content to Web Control lblResults.text = “Guess correctly.” lblResults.Text property Display updated
  60. 60. Decision making and Branching Guess is correct? Yes No “Guess Correctly.” “The hidden number is 8”
  61. 61. If … Then … Else … End If If (Guess is correct?) Then output “Guess Correctly.” Else output “The hidden number is 8” End If Flowchart Pseudocode
  62. 62. Condition If (Guess is correct?) Then output “Guess Correctly.” Else output “The hidden number is 8” End If
  63. 63. Condition Guess is correct? is guess same as hiddenNumber? guess = hiddenNumber Pseudocode Pseudocode VB code
  64. 64. VB Code If … Then … Else … End If If guess = hiddenNumber Then lblResults.Text = “Guess Correctly.” Else lblResults.Text =“The hidden number is 8” End If
  65. 65. Exercise Modify the App 1. to generate hidden number from 11 to 15 instead of 1 to 10. 2. to clear the txtAnswer.Text after each guess. (Hint: “” => blank)
  66. 66. ASP.NET Visual Basic Web Form Introduction 4
  67. 67. Get Started Launch VS2012 New Project: ControlStatus Add new item > Web Form: BtnClick
  68. 68. 6 Labels Textbox Quick and dirty for proof-of-concept: Use the default names provided - TextBox1, Label1 to Label6, CheckBox1, RadioButton1 to RadioButton2 and Button1
  69. 69. The status of each control to be updated on the label next to it
  70. 70. The status of each control to be updated on the label next to it
  71. 71. Quick and dirty for proof-of- concept: Use the properties from the controls directly without using variables.
  72. 72. ASP.NET Visual Basic Web Form Introduction 5
  73. 73. Get Started Launch VS2012 New Project: ConvertMonth2 Add new item > Web Form: MonthName
  74. 74. Set content: cbPopup.Checked = True OR cbPopup.Checked = False
  75. 75. Exercise: use txtMonthInteger.Text use lblResults.Text HINT:
  76. 76. If … Then … End If is cbPopup Checked? Yes Popup: “Month is January” Only need “YES” branch. No need to use “Else” in VB code.
  77. 77. HINT: If cbPopup.Checked = True Then …. EndIf
  78. 78. Checking for valid input Input is 1? Yes No Process normally Input is 2? Yes No Process normally Flowchart Input is 3? Yes
  79. 79. If ... Then … Else If … Then …. Pseudocode If monthNumber = 1 Then Process normally ElseIf monthNumber = 2 Then Process normally ElseIf monthNumber = 3 Then Process normally : End If
  80. 80. Subroutines for code reuse Variables declaration moved to outside the subroutine, so that they can be access from all the subroutines including btnConvert_Click() and myFunc(). Common codes are moved into a new subroutine - myFunc().
  81. 81. If … ElseIf … Else … EndIf Summary
  82. 82. If … ElseIf … Else … EndIf Type 1 If Condition Then Processing End If Type 2 If Condition Then Processing Else Processing End If
  83. 83. If … ElseIf … Else … EndIf Type 3 If Condition1 Then Processing ElseIf Condition2 Then Processing End If Type 3++ If Condition1 Then Processing ElseIf Condition2 Then Processing ElseIf Condition3 Then Processing End If
  84. 84. If … ElseIf … Else … EndIf Type 4 If Condition1 Then Processing ElseIf Condition2 Then Processing Else Processing End If Type 4++ If Condition1 Then Processing ElseIf Condition2 Then Processing ElseIf Condition3 Then Processing Else Processing End If
  85. 85. This is just an introduction. Happy programming!

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