Advanced GIS: functions,Procedures, Arrays and Collections

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Advanced GISfunctions,Procedures, Arrays and
Collections

• Fall 2003

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Functions and subprocedures

• Functions - consist of code that does something
  specific and then return a value to the part of
  the program that called it. For example, the
  Sin() function.
• Subprocedures - dont return results, eg. the
  Unload method. So far, the code we wrote are
  for event subprocedures. When a command button
  named Command1 is pressed, Visual Basic runs
  the Command1_Click() event subprocedure.
  Subprocedure usually does something, like
  changing the display, but it doesnt tend to pass
  anything back to Visual Basic

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Creating a sub procedure

• Two ways to add sub procedure
• 1) Use the Add Procedure dialog box or
• Open the Code Editor window and go to Tools gt Add
  Procedure. Type in Name of the procedure and
  make sure Private scope is checked and click OK
  to continue
• 2) Directly define a procedure in the Code
  Editor window - type in code for a procedure and
  end with End Sub

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Call Procedure

• Using Call Procedure_Name to call procedure.
  You may directly use Procedure without calling
  procedures, but its not recommended.
• Private Sub cmdCalculate_Click()
• intMyNumber InputBox (Input your number)
• Call SquareNumber
• End Sub
• Private Sub mnuToolsCalculate_Click()
• SquareNumber
• End Sub
• Private Sub SquareNumber()
• lblAnswer.Caption intMyNumber intMyNumber
• End Sub

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Passing Arguments to procedures

• Private Sub SquareNumber(intNum As Double)
• lblAnswer.Caption intNum intNum
• End Sub
• Private Sub cmdCalculate_Click()
• intMyNumber InputBox (Input your number)
• Call SquareNumber(intMyNumber)
• End Sub
• Exercise create a sub procedure with two
  arguments for calculating area of a rectangle
• Private Sub Area(x as single, y as single)
• lblAnswer.Caption x y
• End Sub
• Private Sub cmdCalculate_Click() need to
  declare width/height
• width Inputbox (Input width of a square)
• height inputbox (Input height of a square)
• Call Area(width, height)
• End Sub

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Lets create a window menu using Menu Editor

• Add a new form (Project gt Add Form)
• Go to Tools gt Menu Editor and create a two-layer
  menu as shown on right

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Common Dialogs

• Insert Common Dialogs from Project gt Component gt
  Microsoft Common Dialog
• The following are the functions available
• Open file- ShowOpen
• Save File - ShowSave
• Color - ShowColor
• Font - ShowFont
• Print - ShowPrinter
• Help - ShowHelp
• Name this common dialog as dlgFile

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Connect FilegtSave with Common Dialog

• In Code Editor, type in the following code
  associated with mnuFileSave_Click()
• dlgFile.ShowSave

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Exercise

• Add Two menus to your SlideShow(HW8) program
  File and Tools
• Add Save As, and Exit on File menu and SlideShow
  on Tools menu. (mnuFile, mnuFileSaveAs - CtrlS,
  mnuFileExit, mnuTools, mnuToolsSlideShow)
• Add Microsoft Common Dialog Control 6.0 and name
  it as dlgMain (under munFileSaveAs_Click() )
• dlgMain.FileName lstSlides.Text
• dlgMain.ShowSave
• If dlgMain.FileName ltgt Then
• SavePicture imgPicture, dlgMain.FileName
• End If
• SavePicture requires two arguments, first-the
  picture or image control from which the graphic
  file is to be created. The second is the full
  path to the location where the picture file is to
  be saved.

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• use code Unload Me for mnuFileExit (and
  dlgFile.ShowOpen to associate with Open, if Open
  is under File)
• mnuToolsSlideShow_Click() - type a msgbox
  SlidShow has not been implemented yet with
  vbExclaimation
• run this program and save file to different
  location with different file names

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Public or Private

• Public subprocedures are declared like this
• Public Sub ltsubprocedure namegt
• Public Function ltfunction namegt As ltreturn typegt
• A public routine can be accessed throughout the
  program but a private can only called in the same
  Form or Module
• Advantage of using Private
• use less memory, code protected within one
  corner, and names used over and over

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Passing arguments to procedures

• If a procedure requires arguments, they are
  passed to the procedure, when the procedure is
  called. Lets create a Sub called SquareNumber
  with argument and one command button, one text
  box and a label for showing the answer.
• Private Sub SqureNumber (intNum As Double)
• lblAnswer.Caption intNum intNum
• End Sub
• Arguments have to be supplied to run this
  procedure. Lets modify cmdCalculate
• Private Sub cmdCalculate_Click()
• Call SquareNumber (txtNum.text)
• End Sub

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ByRef or ByVal

• Argument s can be passed either by value or by
  reference. Passing by value- a copy of the
  variable is passed to the sub procedure. If the
  variable is changed in the sub procedure, the
  original variable in the calling procedure is not
  affected. If an argument is passed by reference,
  changing the argument in the sub procedure will
  permanently change the argument in the calling
  procedure. ByRef is default, if not specified
• Dim X As Integer
• X 5
• Call aSub(X)
• MsgBox X X
• Private Sub aSub (ByVal Y As Integer)
• Y 6
• End Sub

Try ByRef
Change ByVal to ByRef and see the differences
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Built-in functions

• String, numeric, date and time, financial
  functions.
• Commonly used String functions
• LCase/UCase converts to L/U case
• Len return length of string
• Left/Right/Mid return specified number of cha.
  form left/right/middle side of a string.
• Replace replace one or more occurrence of a
  string inside another
• LTrim/RTrim/Trim removes spaces from the
  beginning (end)(both ends) of a string.
• InStr/InStrRev returns the position of the
  first(last) occurrence of one string within
  another
• Join return a string created by joining a number
  of substrings contained in an array.

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Numeric/Date/Time

• Abs/Sin/Cos/Tan/Atn(arctangent)/Exp/Log/
  Sqr/Sgn(sign of a number)/Rnd (random
  number)/Int,Fix (integer portion of a number)
• Date-current system date
• DateAdd- add specified interval to a date
• DateDiff - differ of two specified dates
• ..
• ..

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Variable Scope
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Static statement - to preserve the values of
procedure-level variables, use Static
VariableName As data type

• used to maintain the values of variables between
  calls of the procedure.
• Try this
• Private Sub Command1_Click()
• Static intNum As Integer
• intNum intNum 1
• MsgBox intNum
• End Sub
• Try to run these code several times, the
  increment of
• intNum can be shown in Static but not Dim

Private Sub Command1_Click() Dim intNum As
Integer intNum intNum 1 MsgBox intNum End Sub
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Option Explicit

• Implicit Declaration - in VB, if no declaration
  for variables. Try the following code
• myVariable 5
• myVariable myVariable 5
• MsgBox myVariable

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Function procedures - return values which
determines data type of functions

• Return a value from a function by assigning it to
  the name of the function itself. Basically, the
  function is treated as though it were a variable.
• In slides 4/5, the SqureNumber sub can only
  change the lblAnswer.Caption. If a function is in
  place such as the follows
• Private Function SqureNumber (intNum As Double)
  As Double
• SquareNumber intNum intNum
• End Function
• Private Sub munToolsCalcualte_Click()
• Dim intMyNumber As Double
• intMyNumber txtNum.Text
• lblAnswer.Caption SqureNumber (intMyNumber)
• End Sub

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Multi-form projects

• Most projects need more than one form. For
  instance, login form, splash form and about form.
  
• To add a new form to a project, choose Add Form
  from the Project menu or right-click in the
  Project Explorer window.
• Form can be referred as Me by procedures within
  the form, and other forms must be referred to by
  their names.
• If a project contains more than one form, a
  startup form must be declared in the Project
  Properties dialog box, accessed from the Project
  menu. (go to ProjectgtProject Properties...)
• If you want the application to start without any
  form initially loaded (e.g., retrieve data
  -gtdisplay one of the form depending on the
  contents of the data file), then create a Sub
  procedure called Main in a standard module and
  select Sub Main as the Startup Object.

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Manage Forms

• Tasks Methods/Statements
• Load/Not Display Load Statement
• LoadDispaly Show method
• Display a loaded form Show method
• Hide/Not unload Hide method
• HidUnload Unload
• Load frmMain or frmMain.Show
• frmMain.Hide or Me.Hide
• Unload frmMain or Unload Me, code portions
  still exist
• Set frmMain Nothing completely terminate the
  form and reclaim memory

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Modal/Modeless Forms

• Most of dialog boxes in VB are modal. Only one
  form can be modal on the screen at one time.
  When a modal form is displayed, the application
  beeps if the user clicks outside the form.
• Modeless form- allows the user to switch to
  another form or dialog box
• With the style argument vbModal or vbModeless,
  the Show method displays a modal or modeless
  form. If you do not specify the style argument,
  the form will be modeless. For example
• Modal form
• frmMain.Show vbModal
• Modeless form, the default
• frmMain.Show vbModeless

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Standard modules

• No GUI, no form, only code.
• Public procedures shared by multiple projects,
  avoid referencing form-specific controls, which
  can be passed as arguments to the general
  procedures of the standard module.
• To call the procedure from outside the standard
  module, directly refer to procedures name, if it
  is unique, otherwise, you need the module name as
  the prefix. To call procedure within own std
  module, simply refer to the procedure name.
• Save the std module with a unique name and .bas
  file extension in the same directory where the
  project file is saved.

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Practice

• Create a new project with form.
• Add standard module from U\4850_5850\ArcObjects\a
  ml_func.bas by checking on ProjectgtAdd Module and
  navigate to this directory.
• Add a command button(cmdParse, CaptionParse),
  textbox (txtInput) and type in code under
  cmdParse_Click()
• Private Sub cmdParse_Click()
• Dim strMyArray() As String
• ParseStringR txtInput.Text, strMyArray
• MsgBox strMyArray(0)
• End Sub

try single quote
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Arrays - used to store a series of elements that
usually contain related information

• Fixed-size array
• Dynamic array
• Multi-dimensional arrays

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1-D fixed array

• Dim My1DFixedArray(4) As String declare array
  with 5 elements
• My1DFixedArray(0) Heart assign value
• My1DFixedArray(1) Club
• My1DFixedArray(2) Spade
• My1DFixedArray(3) Diamond
• My1DFixedArray(4) Club
• MsgBox My1DFixedArray(2) retrieve
• Specify upper/lower bound
• Dim My1DFixedArray(0 to 4) As String
• Dim My1DFixedArray(1 to 4) As String

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Dynamic Arrays - number of elements to be stored
is not known ahead of time
Slide1
Slide2
Slide3
Slide4
....
....
0
1
2
3

• Dim DynArray() As String
• Dim X As Integer
• X InputBox (Enter the number of elements in
  the_ array )
• ReDim DynArray(X-1)

Allow programmer to manage memory more
efficiently than fixed arrays
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ReDim/Preserve/Erase

• The size of array will be specified at run-time
  with keyword ReDim and the memory for the array
  is then allocated. You can change size of
  dynArray anytime with ReDim statements, but the
  original values contained in array are lost once
  encountering ReDim. Use keyword Preserve to
  preserve values.
• ReDim Preserve DynArray (UBound(DynArray) 1)
  this add one element more but preserve previous
  values
• Use Erase to deallocate memory and ReDim to
  reallocate memory. e.g Erase DynArray

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Multi-dimensional arrays

• Path(0) Date(1) Second(2) Title(3)
• Slide(0) C\temp 1/30/89 5 Slide show
• Slide(1) U\4850 3/19/02 4 Rex
• Slide(2) E\temp 3/20/01 6 Trees

Option Explicit Dim Slide() As String Private Sub
Command1_Click() ReDim Slide(0 to 3, 0 to
1) Assign value Slide(col,row)
value Slide(0,0) C\temp Slide(0,1)
1/30/89 Slide(0,2) 5 Slide(0,3) Slide
Show Slide(1,0) U\4850
Add more data ReDim Preserve Slide(3, UBound
(Slide,2) 1)
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Exercise - work with 2-D dynamic arrays

• Create a new Form(frmGrades, Enter Grades), add
  two labels(lblStudentName, Student Name
  lblLetterGrade, Letter Grade), 2 text
  (txtStudent, txtGrade, ), 1 commandbox
  (cmdApply, Apply Grade, Default True),
  Horizontal Scroll Bar (hscStudent, Max0, Min0)
• The application will store students names and
  grades in any array (dynamic). Because the
  values in the array will need to be used in 2
  different procedures. Variables have to be
  declared at the form level. Dim Score() As String
• Store student names in a 2-D dynamic array
  Declare a Static variable Number As Integer
  (maintain the number of students between
  procedure calls)

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Grade

• Private Sub cmdApply_Click()
• Static Number As Integer
• ReDim Preserve Score(1, Number)
• Score(0, Number) txtStudent.Text
• Score(1, Number) txtGrade.Text
• hscStudent.Max Number
• hscStudent.Value Number
• Number Number 1
• End Sub

2-D Array txtStudent.text stored in Score first
column, and txtGrade in 2nd column
hscStudent.Value indicate where the slider of
the horizontal scroll bar is located and act as
the index for the Score array. When you move the
scroll bar slider, the Value property is changed,
and a different element in the Score array is
retrieved and displayed in txtStudent
Private Sub hscStudent_Change() txtStudent.Text
Score(0, hscStudent.Value) txtGrade.Text
Score(1, hscStudent.Value) End Sub
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Collection -an object that does not have a
graphic component, dynamically grows and shrinks

• Dim MyCollection As New Collection
• You can use four methods Add, Remove, Count, and
  Item (Variant is the data type for storing
  different data type)
• Key

MyCollectioin
Index
1 2 3 4
Hello
3.14159
2/7/02
Slide1
Key
strHello Pi dt2/7/02 slide1
Its safer to use the key strings to identify the
items, why?
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Colleciton - 2

• Add NewItem w/o key at the end of the collection
• MyCollection.Add NewItem
• Add NewItem w/ key myNewItem at the end of the
  col.
• MyCollection.Add NewItem myNewItem
• Remove using Index or Key. Index starts from 1
  not 0.
• MyCollection.Remove 5 Remove the fifth item
• MyCollection.Remove myNewItem remove using
  key
• To Change an item, add new item first before or
  after the old item, then remove the old one. e.g.
  change 2/7/02 to 3/20/02
• MyCollection.Add 3/20/02, dt3/20/02,3
• MyCollection.Remove 4 or Remove dt2/7/02
• Set MyCollection Nothing clear collection

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Looping through Collection

• 1) For Each... Next and 2) For....Next
• Dim Thing As Variant
• For Each Thing In MyCollection for each is
  more efficient than for next.
• lstName.AddItem Thing
• Next
• Set Thing Nothing set variant to nothing will
  recollect memory
• Dim I As Integer
• For I 1 to MyCollection.Count
• lstName.AddItem MyCollection.Item(I)
• Next I

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Homework 9-1 30 points, due on 11/6/03.

• Work on your previous homework, if you dont have
  a good vbp file, copy it from data_center\hw9-data
  folder.
• See demo for the tasks to be completed.
• See link on the webpage to get detailed
  description of the homework