Chapter 7 Lists, Loops, and Printing

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Chapter 7Lists, Loops, and Printing

• Programming In
• Visual Basic.NET

2
ListBoxes ComboBoxes

• Provide a list for the user to select from
• Various styles, choose based on
• Amount of data to be displayed
• Space available
• User's ability to add to the list

3
Types of List Controls

• ListBox tool
• 1st prefix
• Simple List Box with/without scroll bars
• ComboBox tool
• cbo prefix
• List may allow for user to add new items
• List may "drop down" to display items in list

CheckedListBox not covered in this text
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List Controls Visually
Dropdown Combo Box
Simple Combo Box
List Boxes
Dropdown List Box
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Choosing List Type

• Many items, little space
• Dropdown Combo Box
• Dropdown List
• Few items
• List Box
• User allowed to add to the list
• Simple Combo Box
• Dropdown Combo Box

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Name and Text Properties

• ListBoxes
• Name displayed at Design Time
• Text accessible only at Run Time
• ComboBoxes
• Text displayed and accessible at Design Time
• Text also accessible at Run Time
• If user enters new data in ComboBox then VB
  stores it temporarily in the Text property

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DropDownStyle Property

• Used to indicate the type of ComboBox
• Dropdown Combo DropDown
• Simple Combo Simple
• Dropdown List DropDownList

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Items Collection

• List of items in a ListBox or ComboBox is a
  collection
• Collections are objects that have properties and
  methods that allow you to
• Add items
• Remove items
• Refer to individual items
• Count items
• Clear the collection

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Index Property

• Zero based value used to reference individual
  items in the collection
• Position of an item in the list
• 1st item Index 0 (1-10)
• 2nd item Index 1 (2-11)
• 3rd item Index 2 (3-12)
• So we can say that . . .
• nth item Index n-1

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SelectedIndex Property

• Use to identify currently selected item in the
  list
• If no item is selected ListIndex -1
• Use to select an item in the list

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Items.Count Property

• Use to determine number of items in the list

Remember Items.Count is the actual number of
items in the list BUT the SelectedIndex property
and Index will be 1 less. For example, it there
are 20 items in the list Items.Count20 BUT Inde
x 19 for the last item in list
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Using the Items Collection

• Use the index of the item to reference a specific
  item in the collection
• Remember that the index is zero based so the 1st
  item in the list is index position zero

lstSchools.Items(5) "USC" ' Next line
references the currently selected
item strSelectedFlavor lstFlavor.Items(lstFlavor
.SelectedIndex)
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Filling a List

• Design time in properties window
• Items property
• Click on ellipses to open String Collection
  Editor
• Separate items with ENTER key
• Run time methods
• Items.Add
• OR
• Items.Insert

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Filling List - Design Time
Click ellipses button to open
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Items.Add Method

• Use to add new items to the list at run time
• General Form
• Examples

Object.Items.Add(ItemValue)
lstNames.Items.Add("Brandon") lstDeptNums.Items.Ad
d(100) cboMajors.Items.Add(txtMajors.Text) 'Next
line adds new item user typed in to
combo cboGrade.Items.Add(cboGrade.Text)
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Items.Insert Method

• Use to add new items to the list at run time at a
  specific location(index) in the collection
• General Form
• Examples

Object.Items.Insert(IndexPosition, ItemValue)
lstDeptNums.Items.Insert(1, 100) cboGrade.Items.in
sert(0, "Freshman") cboMajors.Items.Insert(11,
txtMajors.Text)
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Items.RemoveAt Method

• Use to specific remove items from the list at run
  time by specifying the index of the item
• General Form
• Examples

Object.Items.RemoveAt(IndexPosition)
lstDeptNums.Items.RemoveAt(1) ' Next line
removes the currently selected item cboGrade.Items
.RemoveAt(cboGrade.SelectedIndex)
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Items.Remove Method

• Use to specific remove items from the list at run
  time by specifying the Text of the item
• General Form
• Examples

Object.Items.Remove(TextString)
lstDeptNums.Items.Remove("USC") ' Next line
removes the currently selected item cboGrade.Items
.Remove(cboGrade.Text)
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Clear Method

• Empty the entire list from list box or combo box,
  remove all the items
• General Form
• Examples

Object.Items.Clear( )
lstDeptNums.Items.Clear( ) cboGrade.Items.Clear( )
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ListBox and ComboBox Events

• TextChanged Event
• Occurs when user types text into Combo
• ListBox does not have TextChanged Event
• SelectedIndexChanged Event
• Enter Event (receive focus)
• Leave Event (lose focus)

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Loops

• Repeating a series of instructions
• Each repetition is called an iteration
• Types of Loops
• Do
• Use when the number of iterations is unknown
• For Next
• Use when the number of iterations known

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Do Loops

• Ends based on a condition you specify, either
• Loop While a condition is True
• Loop Until a condition becomes True
• Condition can be located at
• Top of Loop, Pretest
• Bottom of Loop, Posttest

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Do Loop General Form

• Do While Until condition
• Statements to execute
• Loop
• OR
• Do
• Statements to execute
• Loop While Until condition

Top of Loop Condition, Pretest
Bottom of Loop Condition, Posttest
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Do's - When Evaluated

• Top Evaluation, not guaranteed to run once since
  evaluated BEFORE running
• Do While Loop
• Do Until Loop
• Bottom Evaluation, will always run at least one
  time
• Do Loop While
• Do Loop Until

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For Next Loops

• Use when you know the number of iterations
• Uses a numeric counter variable, called Loop
  Index, to control number of iterations
• Loop Index is incremented at the bottom of the
  loop on each iteration
• Step value can be included to specify the
  incrementing amount to increment Loop Index, step
  can be a negative number

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For Next Loop General Form

• For LoopIndex InitialValue To TestValue Step
  Increment
• Statements to execute
• Next LoopIndex

Line continuation not shown on this slide
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Do Loops / For Next LoopsDeciding Which To Use
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Manually Exiting For Next Loops

• In some situations you may need to exit the loop
  prematurely
• Use the Exit For statement inside the loop
  structure
• Generally the Exit For is part of an If statement

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Making Entries Appear Selected

• In Windows, when a user tabs into a text box or
  one of the list controls the data in the control
  is usually selected
• Also, when setting the focus in code to a text
  box or list it is customary to select all the
  data, for example on invalid data during
  validation

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Making Entries Appear Selected (cont.)

• TextBox
• Add the SelectAll method to the TextBoxName_Enter
  event
• ListBox or ComboBox
• Set the SelectedIndex property
• Examine the code listing for p 308 which selects
  matching entries from the list as the user types
  characters

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Sending Data to the Printer

• PrintDocument class
• PrintPreviewDialog class
• Consider using a 3rd party software package for
  printing
• Crystal Reports is a utility packaged with the VB
  Professional and Enterprise Editions for creating
  reports from database files

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PrintDocument Control

• Add PrintDocument controlto form
• Appears in the Component Tray, pane at bottom of
  Form Designer where nondisplay controls are shown
• Name using prt prefix
• Execute the Print method to start printing
• Logic for actual printing belongs in the
  PrintDocument's PrintPage event procedure

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The Printing Saga in .NETSetting Up the Print
Output

• PrintPage event is fired once for each page to be
  printed
• BeginPrint and EndPrint are also fired at the
  beginning and end of the printing
• PrintPage event includes the argument e as
  System.Drawing.Printing.PrintPageEventArgs
• Properties of the PrintPageEventArgs are useful
  for handling page margins and sending strings of
  text to the page

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Private Sub btnPrint_Click(ByVal sender As
System.Object, ByVal e As System.EventArgs)
Handles btnPrint.Click prtDocument.Print()
will print only blank a blanck page
Unless there is a prtDocument_PrintPage(
Which is is fired once for each page to be
printed End Sub
argument e as System.Drawing.Printing.PrintPageEv
entArgs useful for handling page margins and
sending strings of text to the page
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Graphics Page
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Graphics Page
X ?
Y ?

• Set up in memory and then send thepage to the
  printer
• Can contain strings of text and graphic elements
• Specify the exact X and Y coordinates, in pixels,
  of each element to be printed on the page
• X horizontal distance from left edge of paper
• Y vertical distance from top edge of paper

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Graphics Page

• Set up in memory and then send thepage to the
  printer
• Can contain strings of text and graphic elements
• Specify the exact X and Y coordinates, in pixels,
  of each element to be printed on the page
• X horizontal distance from left edge of paper
• Y vertical distance from top edge of paper

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DrawString Method

• Used to send a line of text to the graphics page
• Belongs to the Graphics object of the
  PrintPageEventArgs argument, e
• Is an overloaded method so there are several
  forms (signatures) for calling the method
• Set up the Font to be used before executing the
  DrawString method

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DrawString Method

• Used to send a line of text to the graphics page
• Belongs to the Graphics object of the
  PrintPageEventArgs argument, e
• Is an overloaded method so there are several
  forms (signatures) for calling the method
• Set up the Font to be used before executing the
  DrawString method

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DrawString Method (cont.)
General Form
DrawString(StringToPrint, Font, Brush,
Xcoordinate, Ycoordinate)
Examples
e.Graphics.DrawString(strLine, fntFont,
Brushes.Black, sngX, sngY) e.Graphics.DrawStri
ng("My String", fntMyFnt, Brushes.Red, 100.0,
100.0) e.Graphics.DrawString(txtName.Text, New
Font("Arial", 10), Brushes.Black, sngLeftMargin,
sngCurrentLine)
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PrintPageEventArgs Argument Properties

• MarginBounds
• Code as
• e.MarginBounds.Left
• e.MarginBounds.Right
• e.MarginBounds.Top
• e.MarginBounds.Bottom
• PageBounds
• PageSettings

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Aligning Decimal Columns(code example p 313-314)

• It is important to align the decimal points of
  numeric data
• Proportional Fonts make aligning decimal points
  difficult
• Declare an object as a SizeF Structure
• Use MeasureString method of the Graphics class to
  determine to determine the width of a formatted
  string in pixels

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Print Preview

• Add PrintPreviewDialogcontrol to form
• Appears in the Component Tray, pane at bottom of
  Form Designer where nondisplay controls are shown
• Name using ppd prefix
• Assign the same PrintDocument object you are
  using for printing to it in code
• Execute the ShowDialog method of the
  PrintPreviewDialog control

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Printing Multiple Pages

• Recall that the PrintDocument's PrintPage event
  fires once for each page
• Indicate that there are more pages to print by
  setting the HasMorePages property of the
  PrintPageEventArgs to True

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Static Variables

• Local variable that retain their value for the
  life of the project
• Can be useful for
• Running totals
• Running counts
• Boolean switches
• Storing current page number/count when printing
  multiple pages