More Form Controls

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More Form Controls

• CS0004
• Lecture 20
• Chapter 9.1 and 9.2

2
Admin

• Project 4 Due Wednesday
• April 4th, by midnight
• Project 3 Graded
• Hand back after class
• Class Canceled Next Wednesday
• April 11th

3
Review - Sequential Files

• A sequential file consists of data stored in a
  text file on disk.
• May be created using Notepad
• May also be created directly from Visual Basic

4
Sequential File Modes

• CreateText open for output
• OpenText open for input
• AppendText open for append
• A file should not be opened in two different
  modes at the same time.

5
Exception Handling
6
Try-Catch-Finally Block

• Dim taxCredit As Double
• Private Sub btnComputeCredit_Click(...)
• Handles
  btnComputeCredit.Click
• Dim numDependents As Integer, message As String
• Try
• numDependents CInt(InputBox("How many
  dependents?"))
• Catch
• message "You did not answer the question "
  _
• " with an integer value. We will "
  _
• " assume your answer is zero."
• MsgBox(message)
• numDependents 0
• Finally
• taxCredit 1000 numDependents
• End Try
• End Sub

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Exception Handling and File Errors

• Exception handling can also catch file access
  errors.
• File doesn't exist causes an IO.FileNotFoundExcept
  ion
• If an attempt is made to delete an open file,
  IO.IOException is thrown.

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File Formats

• Line Separated Values (LSV)
• Each value appears on its own line
• Comma Separated Values (CSV)
• Records are stored on one line with a comma
  between each field
• Example
• Bryan Mills, 412.327.9999, 1728 My Street
• Joe Smith, 412.327.8323, 999 East Carson

9
Split Function

• Facilitates working with CSV formatted files.
• Split can convert a line containing commas into a
  String array.
• The 0th element contains the text preceding the
  first comma, the 1st element contains the text
  between the first and second commas, ..., and the
  last element contains the text following the last
  comma.

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Split

• Dim line As String _ Bob,412.232.2321,333 E
  Street
• Dim Employees() As String
• employees line.Split(","c)
• sets the size of employees() to 3
• employees(0) Bob
• employees(1) 412.232.2321
• employees(2) 333 E Street

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Split Comments

• Employees line.Split(",c)
• In this example, the character comma is called
  the delimiter for the Split function, and the
  letter c specifies that the comma has data type
  Character instead of String. (If Option Strict is
  Off, the letter c can be omitted.)
• Any character can be used as a delimiter. If no
  character is specified, the Split function will
  use the space character as delimiter.

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Join Function

• The reverse of the Split function is the Join
  function
• Join concatenates the elements of a string array
  into a string containing the elements separated
  by a specified delimiter.
• Dim greatLakes() As String _
• "Huron","Ontario","Michigan","Erie","Superi
  or"
• Dim lakes As String
• lakes Join(greatLakes, ",")
• txtOutput.Text lakes
• OUTPUT
• Huron,Ontario,Michigan,Erie,Superior

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List Box Review

• lstBox.Items.Count
• Number of items in lstBox
• lstBox.Items.Add(string)
• Adds string to lstBox
• lstBox.SelectedIndex
• Gets the item the user has selected
• lstBox.Items(n)
• Gets the nth item in the lstBox

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List Box Review

• lstBox.Items.RemoveAt(n)
• Remove the item at the nth location
• lstBox.Items.Remove(string)
• Remove ONLY the first occurrence of string in the
  lstBox
• lstBox.Items.Clear()
• Removes all items in the lstBox
• lstBox.Text
• Gets the currently selected item

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The Combo Box Control

• A list box combined with a text box
• The user has the option of selecting from a list
  or typing in something
• Essentially same properties, events, and methods
  as list box

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The Combo Box Control

• Three types of combo boxes in the DropDownStyle
  property

DropDown (and DropDownList) combo box
Simple combo box
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Example 2

• Private Sub btnDisplay_Click(...) _
• Handles
  btnDisplay.Click
• txtDisplay.Text cboTitle.Text " "
  txtName.Text
• End Sub

txtName
cboTitle
txtDisplay
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The OpenFileDialog Control

• Implements the standard File Open dialog box
• Found in the Dialogs section of the Toolbox
• When you place the control on the form, it will
  not be visible.
• The icon and default name will appear in the pane
  below the Main area.

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An Open File Dialog Box
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The Filter Property

• Determines what appears in the Files of type
  combo box, and what types of files will be
  displayed. The setting has the general form
• text for combo box.ext
• Example Text Files (.TXT).TXT

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Using the OpenFileDialog control

• To display the control
• OpenFileDialog1.ShowDialog()
• After the Open button has been pressed, the file
  name selected and its complete filespec will be
  contained in the property
• OpenFileDialog1.FileName

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Example 3 Task

• Select a text file and display its contents.
• Note The Filter property of OpenFileDialog1 is
  set to
• Text Files (.TXT).TXT

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Example 3 Code

• Private Sub btnSelect_Click(...) Handles _
• btnSelect.Click
• Dim textFile As String
• OpenFileDialog1.ShowDialog()
• textFile OpenFileDialog1.FileName
• Dim sr As IO.StreamReader _
• IO.File.OpenText(textFile)
• Do While sr.Peek ltgt -1
• lstOutput.Items.Add(sr.ReadLine)
• Loop
• sr.Close()
• End Sub

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9.2 Seven Elementary Controls

• The Group Box Control
• The Check Box Control
• The Radio Button Control
• The Timer Control
• The Picture Box Control
• The Horizontal and Vertical Scroll Bar Controls

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The Group Box Control

• Group boxes are passive objects used to group
  other objects together
• When you drag a group box, the attached controls
  follow as a unit
• To attach a control to a group box, create the
  group box, then drag the control you want to
  attach into the group box

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Group Box Example
Text property of the group box
Three attached controls Button1 Button2 Button3
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The Check Box Control

• Consists of a small square and a caption
• Presents the user with a Yes/No choice
• During run time, clicking on the check box
  toggles the appearance of a check mark.
• Checked property is True when the check box is
  checked and False when it is not
• CheckedChanged event is triggered when the user
  clicks on the check box

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Example 1 Form
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Example 1 Code

• Private Sub Tally(...) Handles chkDrugs.CheckedCha
  nged, _
• chkDental.CheckedChanged, chkVision.CheckedCha
  nged, _
• chkMedical.CheckChanged
• Dim sum As Double 0
• If chkDrugs.Checked Then
• sum 12.51
• End If
• If chkDental.Checked Then
• sum 9.68
• End If
• If chkVision.Checked Then
• sum 1.5
• End If
• If chkMedical.Checked Then
• sum 25.25
• End If
• txtTotal.Text FormatCurrency(sum)
• End Sub

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Example 1 Output
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The Radio Button Control

• Consists of a small circle with a caption (that
  is set by the Text property)
• Normally several radio buttons are attached to a
  group box
• Gives the user a single choice from several
  options
• Clicking on one radio button removes the
  selection from another

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Radio Button Properties

• To determine if the button is on or off
• radButton.Checked
• has value True if button in on.
• To turn a radio button on
• radButton.Checked True

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Example 2 Form
radCandidate1
radCandidate2
txtVote
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Example 2 Code

• Private Sub btnVote_Click(...) Handles
  btnVote.Click
• If radCandidate1.Checked Then
• txtVote.Text "You voted for Kennedy."
• ElseIf radCandidate2.Checked Then
• txtVote.Text "You voted for Nixon."
• Else
• txtVote.Text "You voted for neither."
• End If
• End Sub

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Example 2 Output
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The Timer Control

• Invisible during run time
• Triggers an event after a specified period of
  time
• The Interval property specifies the time period
  measured in milliseconds
• To begin timing, set the Enabled property to True
• To stop timing, set the Enabled property to False
• The event triggered each time Timer1.Interval
  elapses is called Timer1.Tick.

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Example 3 Form
txtSeconds
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Example 3 Code

• Private Sub btnStart_Click(...) Handles
  btnStart.Click
• txtSeconds.Text "0" 'Reset watch
• tmrWatch.Enabled True
• End Sub
• Private Sub btnStop_Click(...) Handles
  btnStop.Click
• tmrWatch.Enabled False
• End Sub
• Private Sub tmrWatch_Tick(...) Handles
  tmrWatch.Tick
• txtSeconds.Text CStr((CDbl(txtSeconds.Text)
  0.1))
• End Sub

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Example 3 Output