ArcObjects

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ArcObjects

• Sara Alspaugh
• EVSC 468
• 27 March 2007

2

• What? Why? How?
• Where? When? What? Why? What?

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What

• ArcObjects is the development platform for the
  ArcGIS family of applications such as ArcMap,
  ArcCatalog, and ArcScene. The ArcObjects software
  components expose the full range of functionality
  available in ArcInfo and ArcView to software
  developers.
• ArcObjects is a framework that lets you create
  domain-specific components from other components.
  The ArcObjects components collaborate to serve
  every data management and map presentation
  function common to most GIS applications.
  ArcObjects provides an infrastructure for
  application customization that lets you
  concentrate on serving the specific needs of your
  clients.
• ESRIs ArcObjects Online help system
• Built using Microsofts Component Object Model
  (COM) technology.

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What?
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Hmmlets start with just Objects

• Look at it like this
• What do we use computers to do?
• Store data
• Perform functions
• So they came up with this new way to think
  about and design software
• Objects!
• Encapsulate data and functions
• Just like objects in the real worldcan be any
  sort of object
• For instance, imagine a list. No,a List.
• Its an object
• We want to use it to store various pieces of
  information, likethe length of the list (a
  number), the items in the list (other objects
  maybe?)
• Also we want it to perform certain functionslike
  clear() itself, insert(anItem), and tell us its
  length().

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You may be thinking

• Wow thats pretty obvious.
• What did they do before?
• Answer
• Functional programming

• Instead of objects containing data and
  procedures, just have procedures, that take as
  input other procedures and output other
  procedures and have rules for evaluating those
  procedures and blah blah blah blah
• Like algebra. Kind of.
• Much harder (!) to write programs this way.

Yucky!
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Anywayan Example Object

• Say we need some way to write a program that
  keeps the time
• We can make a Clock object!
• How create a type of that object that generally
  specifies how all clocks are to work, then create
  an instancean actual individual objectof that
  type

Class (or Interfce) Clock Data Integer
hours Integer minutes Integer
seconds String meridiem Functions makeClock(
) makeCopy(aClock) getTime() resetTime(newHo
ur, new Minute, new Second)
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So back to ArcObjects
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What about the rest of the definition?

• Component Object Model (COM) a platform for the
  realization of Object-Oriented Development and
  Deployment
• Microsoft lackey who wrote the Wikipedia article
  on Component Object Model

• A protocol or standard
• More than a technology
• A methodology
• A client-server architecture

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(cont.)

• A way to produce reliable, reusable,
  language-independent codeat the binary level
• Essentially, the server is this binary file that
  contains this code needed to create classes of
  objects and run their methods or procedures
• The objects are the building blocks of any
  software system, and the COM specifies the model
  and requirements for creating them that allows
  them to do what they do

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How?

• RPC remote procedure call technology
• IDL interface description language
• GUID globally unique identifier
• Type Library
• ClassFactories

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Remote Procedure Call technology

• Allows a computer program to cause a procedure to
  execute in another address space
• A.k.a. in another computer
• A.k.a. the program makes something happen on
  another computer
• In other words, it is the paradigm for
  implementing this client-server architecture we
  talked about
• A remote procedure call starts by the client
  (you, or the developeractually your computer)
  sending a request message to a known server
  (ArcObjects!) in order to execute some procedure
  you want to execute using parameters you supply.
  The server then gives a response to the client
  and the client continues along with what it was
  doing.

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Hey! I want to do this one thing. Here, use
these parameters or whatever.
parameters
Ok...go ahead. Heres how to do it, I guess.
There, its done.
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Interface Description Language

• The client and server may not be speaking the
  same language. They may not even be operating on
  the same system. How do they get around that?
• A computer language to describe software
  components interface (the specification thing
  that says what they are supposed to look like and
  do) in a language-neutral way
• Thereby enabling communication between software
  components that are written in different
  languages!
• Interface Description Language files are used to
  generate the code to interface between the client
  and the server.

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Hei! Ik wil dit een ding doen. Gebruik hier deze
parameters of wat dan ook.
parameters
Ok ... ??????????????,???????,????
The language-neutral IDL file
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Ok

• COM provides an IDL file
• This allows developers to define their objects in
  a language-independent manner
• P.S
• COM is a run-time framework
• What does that mean?
• Means the types of objects must be identifiable
  at run-time
• Oh ok.

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GUID

• How can we ever possibly identify ever single
  different type of object there is?
• Globally Unique IDever object has one.
• Amounts to a 128-bit number guaranteed to be
  unique in the world.
• An example number
• E6BDAA76-4D35-11D0-98BE-00805F7CED21
• 1110 0110 1011 1101 1010 1010 0111 0110 0100 1101
  0011 0101 0001 0001 1101 0000 1001 1000 1011 1110
  0000 0000 1000 0000 0101 1111 0111 1100 1110 1101
  0010 0001
• Interesting fact It is possible to generate 10
  million GUIDs per second until the year 5770 A.D.
  and each one would be unique.

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One other thing

• COM provides a Type Library
• Compiled from the IDL definition provided by the
  developer
• Once this library is compiled the language
  compiler must read and appropriately interpret it
  to produce the code necessary for the developer
  to produce the binary code which can be deemed by
  COM part of the COM interface

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How do we start making (COM)/(Arc) objects?

• Need two things
• GUID
• ClassFactory
• This is itself a COM object that is contained
  within the servers executable code that creates
  other objects given their unique ID
• Each object type has its own ClassFactory
• Waitif you need a ClassFactory to produce an
  object but a ClassFactory is itself an object?
• DLLdynamic link libraries
• EXEexecutables
• Basically there are two different ways to expose
  class factories but we wont get into that

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My Graphical Overview
Framework
CoRegisterClassObject()
Components
DllGetClassObject()
SimpleDisplay
SimpleMarkerSymbol
GUID
ClassFactory
Tool
IndexGrid
GUID
GUID
GUID
PolygonElement
GUID
SimpleRenderer
Type Library
My Application
GUID
GUID
Client
Server
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Common Approaches

• Customize ArcGIS Desktop applications through
  Visual Basic for Applications (VBA) which is
  embedded in ArcMap and ArcCatalog
• Building targeted applications that bypass the
  application framework of ArcMap and ArcCatalog

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Some of the many topics I didnt cover involving
some of what you might need to know to start
developing using Visual Basic (first approach)

• User-interface standardsVariable
  declarationSuggested naming standardsParentheses
  Order of conditional determinationIndentationDe
  fault propertiesIntermodule referencingMultiple
  property operationsArraysBitwise operatorsType
  suffixesAmbiguous type matchingSimple image
  displayError handlingEvent functions

• While Wend constructsThe Visual Basic Virtual
  MachineInteracting with the IUnknown
  InterfaceAccessing ArcObjectsWorking With
  HRESULTsWorking with propertiesWorking with
  methodsWorking with eventsPointers to valid
  objects as parametersPassing data between
  modulesUsing the TypeOf keywordUsing the Is
  operatorIterating through a collection

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Some of the many topics I didnt cover involving
some of what you might need to do it the second
way

• CODING STANDARDSGENERAL CODING TIPS AND
  RESOURCES   Class diagrams   Object
  browsers   Component help   Code
  wizards   Indexing of collections   Accessing
  collection elements   Enumerator use   Error
  handling   Notification interfaces   Client
  side storage   Property By Value and By
  Reference   Initializing Outbound Interfaces

• DATABASE CONSIDERATIONS   Edit sessions   Edit
  operations   Recycling and nonrecycling
  cursors   Fetching properties using query
  filters   Marking changed objects   Update and
  insert cursors   Shape and ShapeCopy geometry
  propertyUSING A TYPE LIBRARYCOM DATA
  TYPESUSING COMPONENT CATEGORIESWHICH
  DEVELOPMENT ENVIRONMENT

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Programming in VB.NET--a simple walkthrough

• Create a new class library
• Reference the ESRI object libraries
• Create a zoom-in command
• Add Imports statements
• Implement the ICommand interface
• Adding code to the members of ICommand
• Returning the ICommandBitmap property
• Expose the ZoomIn class to COM
• Adding COM category registration functions
• Compiling the project
• Use the command in ArcMap
• Stepping through the command with the debugger

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• Public Class ZoomIn
•     Implements ICommand
•    
•     Private m_app As IApplication
•     Private m_enabled As Boolean
•     Private m_bitmap As System.Drawing.Bitmap
•     Private m_hBitmap As IntPtr    
•     Region "COM GUIDs"    ...
• Public Sub OnCreate(ByVal hook As Object)
  Implements ICommand.OnCreate
•      If Not (hook Is Nothing) Then
•         If TypeOf (hook) Is IMxApplication Then
•            m_app CType(hook, IApplication)
•            m_enabled True
•         End If
•      End If
•    End Sub
•  

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• Public Sub OnClick() Implements ICommand.OnClick
•      Dim mxDoc As IMxDocument
  CType(m_app.Document, IMxDocument)
•      Dim activeView As IActiveView
  mxDoc.ActiveView
•  
•      Dim currExtent As IEnvelope
  activeView.Extent
•      currExtent.Expand(0.5D, 0.5D, True)
•      activeView.Extent currExtent
•      activeView.Refresh()
•    End Sub
• Public ReadOnly Property Caption() As String
  Implements ICommand.Caption
•      Get
•         Return "Zoom In x 0.5 VB.NET"
•      End Get
•    End Property
•  
•    Public ReadOnly Property Category() As String
  Implements ICommand.Category
•      Get
•         Return "Developer Samples"
•      End Get

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• Public ReadOnly Property Enabled() As Boolean
  Implements ICommand.Enabled
•      Get
•         Return m_enabled
•      End Get
•    End Property
•  
•    Public ReadOnly Property HelpContextID() As
  Integer Implements ICommand.HelpContextID
•      Get
•         Return 0
•      End Get
•    End Property
•  
•    Public ReadOnly Property HelpFile() As String
  Implements ICommand.HelpFile
•      Get
•        
•      End Get
•    End Property
•  
•    Public ReadOnly Property Message() As String
  Implements ICommand.Message

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Programming in C--a simple walkthrough

• Create a new class library
• Reference the ESRI object libraries
• Create a zoom-in command
• Add a using directive
• Adding code to the members of ICommand
• Returning the ICommandBitmap property
• Expose the ZoomIn class to COM
• Adding COM category registration functions
• Compiling the project
• Use the command in ArcMap
• Stepping through the command with the debugger

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• public class ZoomIn ICommand   private
  IApplication m_app private bool m_enabled
  private System.Drawing.Bitmap m_bitmap private
  IntPtr m_hBitmap
•    public void OnCreate(object hook)
•   
•      if (hook ! null)
•     
•         if (hook is IMxApplication)
•        
•            m_app (IApplication) hook
•            m_enabled true
•        
•     
•   

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• public void OnClick()
•   
•      IMxDocument mxDoc (IMxDocument)
  m_app.Document
•      IActiveView activeView mxDoc.ActiveView
•     
•      IEnvelope currExtent (IEnvelope)
  activeView.Extent
•      currExtent.Expand(0.5D, 0.5D, true)
•      activeView.Extent currExtent
•      activeView.Refresh()  
•   
• public string Caption
•    get
•   
•        return "Zoom In x 0.5 C"
•    
• public string Category

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• public bool Checked
•   
•      get
•     
•         return false
•     
•   
•    public bool Enabled
•   
•      get
•     
•         return m_enabled
•     
•   
•    public string Message
•   
•      get
•     
•         return "Zooms the display to half the
  current extent."

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Review!

• What is/are ArcObjects?
• A framework
• A collection of component objects
• Fairly useful depending on who you are
• All of the above
• What does COM stand for?
• Corruption of Microsoft
• Communicatiemiddel Oot Maandag
• Component Object Model
• Computer Operating Machinery

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References

• http//edndoc.esri.com/arcobjects/8.3/
• http//en.wikipedia.org/wiki/Component_Object_Mode
  l
• http//en.wikipedia.org/wiki/Remote_procedure_call
  
• http//www.songwriting-software.com/images/iMac20
  computer.jpg
• http//i.cnn.net/cnn/2003/TECH/05/26/your.tech.del
  l/story.dellcomputer.jpg