Programming for GIS

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Programming for GIS

• Keith T. Weber, GISP
• GIS Director, ISU

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Additional Controls and Objects

• List Boxes, Combo Boxes, and the File-Opening
  Control
• Four Elementary Controls
• MDI

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List Boxes, Combo Boxes, and the OpenFile Control

• The List Box Control
• The Combo Box Control
• The OpenFileDialog Control

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The List Box Control

• Items can be placed into the list at design time
  or run time
• The Sorted property causes items in the list to
  be sorted automatically
• If the Sorted property is set to True, then the
  following will place an item into the list in
  order and assign the index of its position to
  num
• num lstBox.Items.Add(str)

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Useful Properties of the List Box

• For the total number of items in a list box
• lstBox.Items.Count
• Note Each item in lstBox is identified by an
  index number from 0 to lstBox.Items.Count - 1
• For the index number of the currently highlighted
  item
• lstBox.SelectedIndex

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More List Box Properties

• lstBox.Items() is the list of items in the list
  box.
• The value of the item with an index of n is
• lstBox.Items(n)
• The data type of the elements in the
  lstBox.Items() array is Object. To put the first
  element of lstBox.Items in a text box
• txtBox.Text CStr(lstBox.Items(0))

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Currently Highlighted Item in a List Boxes

• The currently highlighted item can be obtained
  as
• lstBox.Items(lstBox.SelectedIndex)
• Or
• lstBox.Text

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Removing Items from a List Box

• To delete an item at a given location
• lstBox.Items.RemoveAt(n)
• To delete the first occurrence of an item
• lstBox.Items.Remove(str)
• To remove everything from a list box
• lstBox.Items.Clear()

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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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The OpenFileDialog Control

• Implements the standard File Open dialog box
• Found in the Dialogs section of the Toolbox
• Note 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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An Example

• 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 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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Four Elementary Controls

• The Group Box Control
• The Check Box Control
• The Radio Button Control
• The Timer Control

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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 2 Form
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Example 2 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 2 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 3 Form
radCandidate1
radCandidate2
txtVote
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Example 3 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 3 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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Multiple Forms

• Visual Basic programs can contain more than one
  form
• To add the new form, select Add Windows Form from
  the Project menu, to invoke the Add New Items
  dialog box.

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Add New Items dialog box
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Add New Items dialog box

• Select Windows Form from the Installed Templates
  pane.
• Optionally type in a name.
• Press the Add button.

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Solution Explorer

• Both forms will be accessible through Solution
  Explorer.

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Variables and Multiple Forms

• Variables declared in the declarations section of
  a form with Public, instead of Dim, will be
  available to all forms in the program.
• When a Public variable is used in another form,
  it is referred to by an expression such as
• secondForm.variableName

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Key Concepts

• There are numerous controls that can be placed on
  your GUI. Each has specific purposes. You
  should understand how to choose the best control
  for your needs.

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Questions?