Post on 17-Jul-2015
ASP.NET Visual BasicWeb Form Introduction 1
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
What we will cover
● Variables: valid and invalid variable naming● Data types: Integer, String, Boolean,
Decimal● Decision making using IF … ElseIf … Else
… End If
Tool: Visual Studio 2012 or 2013
● Download a FREE Visual Studio Expresshttps://www.visualstudio.com/en-us/products/visual-studio-express-vs.aspx
● Launch Visual Studio and click on “New Project””.
DateAndTimeApp
New Web Form: PageLoad
New Web Form: PageLoad
Go to Code behind page
● Click anywhere outside the Div box to go to the “Code Behind”file:
PageLoad.aspx.vb
Name of the auto-generated code behind file always same as the Web Form (PageLoad.aspx) and add “.vb” extension
Class and End Class
Every Web Form is an Object.To define an object use “Class” and “End Class”
What does a Class contain?
Eg: Label Class
What is Constructor
When Label icon on the ToolBox is double click => to create a Label object on the page
What are Properties
What are Events
What are Methods
Group of processing that we could ask the object to do
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.
Namespace (x.y.z) to prevent conflictInstead 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.
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..
Page_Load Subroutine Our Program to be added here. Will
be executed every time
the web form Page is Loaded!
Our first App
When the application is run1. 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.”
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:
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.
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.
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,
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.
Declare
You declare a variable using the Dim and As keywords, as shown here.
Dim aNumber As Integer
Variable Type
Assign
aNumber = 42
Declare and Assign
Dim aNumber As Integer = 42
Avoid KeywordsAvoid using keywords as variable Eg Dim, As, Integer, String, etc http://alturl.com/ix85i
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
Valid & Invalid variable names
Validix_special_powera1alien1
Invalidspecial powerspecial-power1alienreg#
Data Types
http://alturl.com/6vg9j
● Boolean for true and false● Decimal● Integer● String● Date::
Modify our app
When the application is run1. 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.”
Exercise: Try to do it on your own!
When the application is run1. 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.”
Variables and Strings
Summary
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
Valid & Invalid variable names
Validix_special_powera1alien1
Invalidspecial powerspecial-power1alienreg#
Declaration of VariablesDim fruit As StringDim weight As StringDim contact As StringDim 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!
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?
“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
“An ” & “apple a day ” & “keep doc away!”
will combine the three strings into one longer string:“An apple a day keep doc away!”
Variables and Strings
fruit = “apple”
weight = “75”
“I like ” & fruit & “ and my wt in kg is ” & weight
“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”
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
ASP.NET Visual BasicWeb Form Introduction 2
Get Started
Launch VS2012New Project: DateAndTimeApp2Add new item > Web Form: LoadPage2
Double click anywhere outside the “Div” box, to generate the *.vb code file.
First attempt
When the application is run1. Output a message: “Time now is xx:xx:xx
AM”
Libraries provided by Microsoft
Before you reinvent the wheel and start to type straight away, look for a suitable one from the libraries provided:
output = “Time now is ” & TimeOfDay
“Time now is 09:15:36 AM”
The combine string is assigned to output
Step 1
Step 2
Modify App
When the application is run1. 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.
Parameters
Exercise: Try to do on your own!
When the application is run1. 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.
ASP.NET Visual BasicWeb Form Introduction 3
Get Started
Launch VS2012New Project: GuessNumberAdd new item > Web Form: BtnClick
Switch the web form to “Design View”. Then drag the various control from the Toolbox window. finally set their properties using the Properties Window.
Page TitleMethod 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.
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.
Get content from Web Control
guess = txtAnswer.Text
txtAnswer.Text property
Set content to Web Control
lblResults.text = “Guess correctly.”
lblResults.Text property
Display updated
Decision making and Branching
Guess is correct?
Yes
No
“Guess Correctly.”“The hidden number is 8”
If … Then … Else … End IfIf (Guess is correct?) Then output “Guess Correctly.”
Else output “The hidden number is 8”
End If
Flowchart Pseudocode
Condition
If (Guess is correct?) Then output “Guess Correctly.”Else output “The hidden number is 8”End If
Condition
Guess is correct?
is guess same as hiddenNumber?
guess = hiddenNumber
Pseudocode
Pseudocode
VB code
VB CodeIf … Then … Else … End If
If guess = hiddenNumber Then lblResults.Text = “Guess Correctly.”
Else lblResults.Text =“The hidden number is 8”
End If
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)
ASP.NET Visual BasicWeb Form Introduction 4
Get Started
Launch VS2012New Project: ControlStatusAdd new item > Web Form: BtnClick
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
The status of each control to be updated on the label next to it
The status of each control to be updated on the label next to it
Quick and dirty for proof-of-concept: Use the properties from the controls directly without using variables.
ASP.NET Visual BasicWeb Form Introduction 5
Get Started
Launch VS2012New Project: ConvertMonth2Add new item > Web Form: MonthName
Set content:cbPopup.Checked = True ORcbPopup.Checked = False
Exercise:
use txtMonthInteger.Text
use lblResults.Text
HINT:
If … Then … End If
is cbPopup Checked?
Yes
Popup: “Month is January”
Only need “YES” branch.
No need to use “Else” in VB code.
HINT: If cbPopup.Checked = True Then …. EndIf
Checking for valid input
Input is 1?
Yes
No
Process normallyInput is 2?
Yes
No
Process normally
Flowchart
Input is 3?
Yes
If ... Then … Else If … Then ….
Pseudocode
If monthNumber = 1 Then Process normallyElseIf monthNumber = 2 Then Process normallyElseIf monthNumber = 3 Then Process normally: End If
Subroutines for code reuseVariables 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().
If … ElseIf … Else … EndIf
Summary
If … ElseIf … Else … EndIf
Type 1If Condition Then Processing End If
Type 2If Condition Then ProcessingElse Processing End If
If … ElseIf … Else … EndIf
Type 3If Condition1 Then ProcessingElseIf Condition2 Then Processing End If
Type 3++If Condition1 Then ProcessingElseIf Condition2 Then ProcessingElseIf Condition3 Then Processing End If
If … ElseIf … Else … EndIfType 4If Condition1 Then ProcessingElseIf Condition2 Then Processing Else Processing End If
Type 4++If Condition1 Then ProcessingElseIf Condition2 Then ProcessingElseIf Condition3 Then ProcessingElse Processing End If
This is just an introduction. Happy programming!