Distance Learning Center

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Distance Learning Center

• Lecture 9
• Introduction to Visual Basic
• Programming
• Melissa Lin, IT Consultant
• HenEm, Inc. Parkville, Missouri
• linm_at_ipfw.edu
• http//www.etcs.ipfw.edu/linm

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Lecture 9

• Input Validation
• Calling procedures
• Hands-On Example
• Debugging

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Input Validation

• The validation is to verify that appropriate
  values have been entered before beginning
  calculations, including checking for numeric
  number, specific values, a range of values
  (reasonableness), or for a required field (not
  blank)
• Performing Multiple Validations
• Using Try/Catch blocks
• Use nested If statement to validate multiple
  values on a form (Examine example on Page 156)
• Using Nested IF statement for performing multiple
  validation
• Using Case structure to validate multiple values

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Input Validation

• Example
• If Integer.Parse(HoursTextBox.Text) gt 10 - to
  check a range of the input
• If nameTextBox.Text ltgt Then to check empty
  field
• If IsNumberic (expression) to check if the data
  is numeric
• If IsNumeric(inputTextBox.Text) True Then
• MessageBox.Show("Good Job of Entering
  Numerical Input")
• Else
• MessageBox.Show ("Whoops, try again")
• End If

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Sharing Event

• Add events to the Handles clause at the top of an
  event procedure
• Allows the procedure to respond to events of
  other controls.
• Key to using a shared event procedure is the
  sender argumentthat is passed to the CheckChanged
  event procedure, such as radio button.
• Cast (convert) sender to a specific object type
  using the CType function.

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Calling Event

• You can call another subroutine from within a
  subroutine
• When you call an event procedure, the entire
  procedure is executed.
• General Form
• Call ProcedureName ( )
• Keyword Call is optional and rarely used
• Example
• Private Sub calculateButton_Click()
• If sevenInteger ltgt 7 Then
• Call exitButton_Click() call the exit event
• EndIf
• Continue with calculations

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Calling Event (continued)

• Call newOrderButton_Click(sender, e)
• OR
• newOrderButton_Click(sender, e)
• Example
• Private Sub summaryButton_Click(ByVal
• sender As System.Object, ByVal e As
  System.EventArgs) Handles summaryButton.Click
• newOrderButton_Click(sender, e)
• Continue with calculations

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Hands-On Programming

• Coffee Sales project - to accumulate individual
  items for one customer. Clearing the entire order
  for the next customer when the customer s order
  is completed, and having a summary
• Adding a Takeout Check Box
• Adding Coffee Selection Radio Buttons
• Five buttons Calculate, Clear, New Order,
  Summary, and Exit
• The steps to write the project
• Define the GUI
• Set the properties of each object as you have
  planned
• Write the code working from the pseudocode, and
  each event procedure
• When completed, to ensure the tab order is set
  correctly
• Save the form
• Save the project
• Run the program

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Planning GUI Design
Coffee Selection
GroupBox1
Quantity
Cappuccino
Takeout
Espresso
latteRadioButton
Calculate
Calculate Selection
Clear for Next Item
Latte
Iced Latte
Iced Cappuccino
GroupBox2
Item Amount
subTotalLabel
Sub Total
Tax (If Takeout)
Total Due
newOrderButton
exitButton
New Order
Exit
Summary
summaryButton
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Place Control on the Form

• Select True at
• Checked for
• Cappuccino

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Plan the Event Procedures

• Procedure Actions
• calculateButton_Click Validate for blank or
  nonnumeric amount
• Find price of drink selection
• Multiply price by quantity
• Add amount to subtotal
• Calculate tax if needed
• Calculate total subtotal tax
• Formal and display the values
• Disable the Takeout check box
• Enable the Clear button
• clearButton_Click Clear the coffee selection
• Clear the quantity and the item price
• Set the focus to the quantity
• Disable the Clear button

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Plan the Event Procedures (continue)
Procedure Actions summaryButton_Click If current
order not added to totals call
newOrderButton_Click Calculate the
average Display the summary totals in a message
box newOrderButton_Click Confirm clearing current
order Clear the current order Accumulate
total sales and count Set subtotal and total due
to 0 Enable Takeout check box Disable the
Clear button exitButton_Click Exit/Terminate the
project
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Write Code Module Level Declaration
Module Level
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Write Code Local Level Declaration
Local Level
NestIf
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Write Code Try/Catch
Try / Catch
Enable
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Write Code MessageBox
messageString "Number of Orders _
customerCountInteger.ToString() _
ControlChars.NewLine ControlChars.NewLine _
"Total Sales "
grandTotalDecimal.ToString("C") _
ControlChars.NewLine ControlChars.NewLine _
"Average Sale " averageDecimal.ToString("C) M
essageBox.Show(messageString, "Coffee Sales
Summary",_ MessageBoxButtons.OK,
MessageBoxIcon.Information)
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Output
Click Calculate
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Output (continued)
After click NewOrder
Click on Clear for Next Item
Click Summary
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Output (continued)
After click Yes
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Debugging
Step Into

• Stop
• Debugging

Step Out
Step Over
Break All
Continue
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Debugging (continue)
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Debugging - Example
Tools -gt Options -gt debugging -gt General -gt In
break

• Break Point

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Debugging Example (continue)

• Message

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Debugging (continue)

• To start debugging / execution
• From the Debug menu, choose Start, Start without
  debugging, Step Into, or Step Over. -or-
• If you choose Start, your application starts up
  and runs until it reaches a breakpoint or an
  exception occurs.
• If you choose to break execution to examine
  values, modify variables, or examine statements
  at your program.
• Place Debug.WriteLine method in your code to
  display the information in the output window.

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Debugging (continue)

• Select Help menu, then select Index

Ex. Type Step Into at Look For Click on Step
Into Command
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Stepping through Code

• The best way to debug a project is to use debug
  stepping tools to trace program execution line by
  line and see the progression of the program as it
  executes through the code.
• Step Into (F11) when the line of code is
  executed each time, the program pauses in break
  time. when the line of code calls to other
  procedures, the first line of code of the other
  procedure displays.
• Step Over (F10) when the line of code calls to
  other procedures, Step Over displays only the
  lines of code in the current procedure being
  analyzed.
• Note the stepping function only works when
  VB.NET is in the Break mode.

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Stepping through Code (continued)

• Step Out when you step through a called
  procedure, the Step Out command continues rapidly
  execution until the called procedure completes,
  and returns to break mode at the statement
  following the call.
• Continuing Program Execution (F5) to continue
  rapid execution and resume the form. Or choose
  the Restart command to restart execution.
• Stopping Execution by selecting Stop Debugging
  to correct the errors and run again

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Hands-On Debugging
Open the Ch04Debug Folder Run it
Enter Quantity 100 with Blue, then click on
Calculate, The Total Blue is 100
Enter Quantity 50 with Blue, then click on
Calculate The Total Blue is 150
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Hands-On Debugging (continue)
Enter Quantity 10 with Red, t hen click on
Calculate The Total Red is 10
Enter Quantity 30 with Red, then click on
Calculate
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Debugging - Set up Break Point Writing to the
Output Window
View the values of properties, variables,
mathematical expressions, and conditions
Click in the gray margin to set a break point at
quantityDecimal
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Debugging (continue)
quantityTextBox 30D
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Writing to the Output Window
Syntax Debug.WriteLine(TextString) Debug.WriteLi
ne(Object) Example If redRadioButton.Checked
Then Debug.WriteLine("Perform
redTotalDecimal") Output Perform redTotalDecimal
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Locals Auto Windows

• Locals Window
• Appears while program is running
• Tab at bottom of VB.NET window
• Autos Window
• Appears while program is running
• Tab at bottom of VB.NET window
• displays variables used in the current statement
  and the previous statement

Autos Window
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Debugging Step by Step
redTotalDecimal 30D quantityDecimal 30D
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An Step by Step Example
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An Step by Step Example
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Correction
redTotalDecimal quantityDecimal
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Re-Run the Program

• Set Option Explicit On and Option Strict On
• Using step into to find errors
• Correct it and Clear all Breakpoints before
  re-running the project

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Output
Before click on Calculate button
After click on Calculate button
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Summary

• Input Validation
• Calling procedures
• Hands-On Example
• Debugging
• Next chapter 5

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Question?

• Answers
• linm_at_ipfw.edu