Visual Basic: Data

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Lecture 10

• Visual Basic Data

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This Lecture

• Data access.
• Getting Maps and Layers
• Getting Attributes
• Selecting Features
• More GUIs Forms
• Help

3
Data Access

• The ArcMap Object model
• Application
• Document / MxDocument type Object
• Display / AppDisplay type Object
• Document
• Maps, FocusMap, ActiveView, StyleGallery
• Well look at
• Getting the Maps, Layers, Features.
• Getting Attribute data.
• Selecting and getting selected Features.

4
Getting data

• Various levels

Map
AttributeTable
Layer
Feature
234
Values
5
Getting a Map

• A Map contains all the data and features in the
  Data View or each Layout View Frame.
• Dim pDoc As IMxDocument
• Set pDoc ThisDocument
• Dim pMap As IMap
• Set pMap pDoc.FocusMap
• FocusMap is the one visible in data view or
  selected in layout view.

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Getting all Maps

• You can also get an Object containing all the
  Maps.
• Dim pDoc As IMxDocument
• Set pDoc ThisDocument
• Dim pMaps As IMaps
• Set pMaps pDoc.Maps
• The Maps object is exposed by the IMxDocument
  Interface.
• It returns an IMaps Interface type Object

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IMaps

• You can loop through all the IMap Interface
  objects in an IMaps Interface object using its
  .count and .item Methods.
• Dim pMap As IMap
• For i 0 To pMaps.count -1
• Set pMap pMaps.item(i)
• Do stuff to pMap
• Next
• Other IMaps Methods include
• Add, Create, Remove(IMap), RemoveAt(index), Reset
  Remove all.

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Getting data

• Its rare we want to get data out of a Map. Its
  more usual to get data from a Layer (a
  Coverage, FeatureDataset, Image etc.).

Map
AttributeTable
Layer
Feature
234
Values
9
Getting Layers

• If you know what the type of the Layers are, you
  can get them thus
• Dim pMxDocument As IMxDocument
• Set pMxDocument Application.Document
• Dim pMap As IMap
• Set pMap pMxDocument.FocusMap
• Dim pLayer As ILayer
• For i 0 To pMap.LayerCount - 1
• Set pLayer pMap.Layer(i)
• Do something
• Next

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Types of Layer

• Remember however that we can add many things as
  Layers (images, data, etc.).
• If we dont know the data type we need to filter
  our Layers before we try to do some job.
• We do this by knowing the number by which the
  system refers to the Layer Classes as.
• This is quite painful.

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Types of Layer

• IDataLayer
• 6CA416B1-E160-11D2-9F4E-00C04F6BC78E
• IGeoFeatureLayer
• E156D7E5-22AF-11D3-9F99-00C04F6BC78E
• IGraphicsLayer
• 34B2EF81-F4AC-11D1-A245-080009B6F22B
• IFDOGraphicsLayer
• 34B2EF85-F4AC-11D1-A245-080009B6F22B
• ICoverageAnnotationLayer
• 0C22A4C7-DAFD-11D2-9F46-00C04F6BC78E
• IGroupLayer
• EDAD6644-1810-11D1-86AE-0000F8751720
• Layers that implement IDataLayer include
  FeatureLayers, FDOGraphicsLayers (Annotation),
  TinLayer, RasterLayer, and CoverageAnnotationLayer
  .

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Enumerations

• Objects containing lists of other objects. Like a
  1D array.
• Arc uses them to return arrays of data to you.
• Have a next Method to get the next Object.
• Also a reset Method to return to the start.
• Arc Object types have different Enumerations.
• IEnumFeature is the Interface for a set of Map
  IFeatures.

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Standard use of Enumerations

• Dim pEnumSomething As IEnumSomething
• Set pEnumSomething someEnumGettingMethod
• pEnumSomething.Reset
• Dim variable As Something
• Set variable pEnumSomething.Next
• Do While Not variable Is Nothing
• Do stuff with Layer
• Set variable pEnumSomething.Next
• Loop

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How to filter Layers
Dim pMxDoc As IMxDocument Dim pMap As IMap Set
pMxDoc Application.Document Set pMap
pMxDoc.FocusMap

• Get an Enumeration of Layers
• Dim pUID As IUID
• Set pUID New UID
• pUID "E156D7E5-22AF-11D3-9F99-00C04F6BC78E
• Dim pEnumLayer As IEnumLayer
• Set pEnumLayer pMap.Layers(pUID, True)
• pEnumLayer.Reset
• Dim pGeoFeatureLayer As IGeoFeatureLayer
• Set pGeoFeatureLayer pEnumLayer.Next
• Do While Not pGeoFeatureLayer Is Nothing
• Do stuff with Layer
• Set pGeoFeatureLayer pEnumLayer.Next
• Loop

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The TypeOf Keyword

• You can check whether an Object implements an
  Interface using VBs TypeOf keyword.
• For example, if the users selected something in
  ArcMap's tree of contents, you can test whether
  its a GeoFeatureLayer, thus
• Dim pUnk As IUnknown
• Set pUnk pEnumLayer.Next
• If TypeOf pUnk Is IGeoFeatureLayer Then
• Set pFeatLayer pUnk
• 'Do something with pFeatLayer
• End If

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Getting data

• Once we have our Layer, we want to get data from
  it.

Map
AttributeTable
Layer
Feature
234
Values
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Getting Features from Layers

• Assign your Layer to an appropriate Interface.
• IGeoFeatureLayer Treat as Geographical data
• IFeatureLayer Treat as a general Layer
• IAttributeTable Treat as an Attribute table
• Search the Layer, or get the Attribute Table.

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Getting the Attribute Table

• Assuming we have a Layer Enumeration, we set the
  Layer to an IAttributeTable.
• Dim pAttributeTable As IAttributeTable
• Set pAttributeTable pEnumLayer.Next
• Dim pTable As ITable
• Set pTable pAttributeTable.AttributeTable
• Dim pRow As IRow
• For i 0 To pTable.RowCount(Nothing) - 1
• Set pRow pTable.GetRow(i)
• Dim index As Long
• index pTable.FindField("School")
• Debug.Print pRow.Value(index)
• Next i

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Getting the Attribute Table

• Assuming we have an Enumeration of Layers
• Dim pAttributeTable As IAttributeTable
• Set pAttributeTable pEnumLayer.Next
• Dim pTable As ITable
• Set pTable pAttributeTable.AttributeTable
• Dim pRow As IRow
• For i 0 To pTable.RowCount(Nothing) - 1
• Set pRow pTable.GetRow(i)
• Dim index As Long
• index pTable.FindField("School")
• Debug.Print pRow.Value(index)
• Next i

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Getting data

• Alternative is to get data from a Feature.

Map
AttributeTable
Layer
Feature
234
Values
First though, we need to get only the features we
are interested in. We can search for these.
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Searching

• You need to get a reference to the data and a
  search cursor (ICursor / IFeatureCursor).
• The search cursor jumps between records in a
  dataset that match some search criteria.
• The cursor marks the row in the dataset that
  youre currently interested in.
• They have a nextFeature Method which gets a
  Feature object appropriate to the Dataset.

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Search Methods

• IFeatureLayer / IGeoFeatureLayer
• Set pCursor pFeatureLayer.Search(Q, False)
• ITable from an IAttributeTable
• Set pCursor pTable.Search (Q, False)
• Where pCursor is an IFeatureCursor Object
• Q is an IQueryFilter Object
• True / False determines how the records are
  allocated to the Cursor set to False.

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IQueryFilter Objects

• You can get everything by setting these to
  Nothing.
• Set pC pFeatureLayer.Search(Nothing, False)
• IQueryFilter Objects store fields you want
  returned and query strings.
• pQueryFilter.SubFields SCHOOL,LEA
• pQueryFilter.AddField (POSTCODE)
• pQueryFilter.WhereClause LEA Leeds
• By default the fields are set to i.e. all
  fields, so if you use just AddFields youll have
  to set SubFields to first.

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Getting Data from a Feature

• Use the cursor to get the next feature
• Dim pFeature As IFeature
• Set pFeature pC.NextFeature
• Do While Not pFeature Is Nothing
• Set pFeature pC.NextFeature
• Do stuff to pFeature
• Loop
• The Feature Method getValue(i) takes in an
  integer number equalling the position of the
  field column.
• If you dont know it, there are lookup methods
  that return integers
• pFeature.Fields.FindField("SCHOOL")

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Setting/Getting Features Selected

• An alternative is to get the selected Features.
• IMaps SelectFeature method takes in an ILayer
  and IFeature.
• Refresh the display using the MxDocuments
  refresh.
• pDoc.ActiveView.Refresh
• To get the Features you need IMaps
  FeatureSelection Method, or an ISelectionSet
  Object see handout for example.

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Getting data

• Various levels

Map
AttributeTable
Layer
Feature
234
Values
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Summary

• Get the Applications Document.
• Get the Maps from it.
• Pick the one you want or loop through them.
• Get a Layer from the Map, or Loop through all of
  them.
• Generate an Attribute table and use Rows / Fields
  to get data.
• Or use the Layers search routine to search for
  Features.

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So far

• Data access.
• Getting Maps and Layers
• Getting Attributes
• Selecting Features
• Now
• More GUIs Forms

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Forms

• Even easier than UIControls. Instead of a Module,
  add a Form.
• Brings up the Form editor drag stuff in.
• Change its properties (which are variables you
  can alter on the fly)
• Double click on Objects to alter Event Methods.

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The Text Box

• One useful item you get with Forms is a TextBox.
• For multiple lines you need to set MultiLine as
  True in its Behaviour properties and give it
  scrollbars.
• You can then set the text in an Event handling
  method, thus
• MyForm.TextBox1.Text Its huge vbCrLf
  Its green

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Running Forms

• Add in a Macro to the document
• Sub startF ()
• MyForm.Show
• End Sub

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So far

• Data access.
• Getting Maps and Layers
• Getting Attributes
• Selecting Features
• More GUIs Forms
• Now
• Help

33
Finding out about Objects

• The Object Browser / Autocompletion lists
• Unfortunately, these dont display methods of
  Class Objects whos default Interface is
  IUnknown. As this is most of the ESRI Objects
  this is not so useful.
• Alternatives
• The ESRI Object Browser
• The Object Help Files / Online Help
• The Object Diagrams

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ESRI Object Browser

• The ESRI Object Browser EOBrowser.exe
• In C\Program Files\ArcGIS\DeveloperKit\tools
• Starts empty of references.

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ESRI Object Browser

• Click whether you want CoClasses, Interfaces etc.
• Search for a term.
• Pick a Class from the list and display it.

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The Object Help Files / Online Help

• The standard VB Editor help files help you with
  VBA but not ArcObjects.
• Two ways to access the ArcObjects help
• Click in a Class or Object and hit the F1 key
  brings up help about that thing.
• Go to the DeveloperKit/help/ directory all the
  help files.
• However, just as easy, and more up to date are
  the online help files at ArcGIS Developer Online
• http//edndoc.esri.com/arcobjects/9.1/

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The Help Files

• ArcGIS Desktop gt Developer Guide
• A good starting point for good practice when
  using ArcObjects naming standards, code to
  avoid etc.
• Object Model / Overview
• Basic descriptions of the branches of the
  Framework and their major classes.
• Library Reference
• Lists of all the Interfaces and Classes for the
  Core bits (Application, ArcMap/Editor, ArcCatalog)

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Help Files

• List Classes / Interfaces and their methods /
  variables

Access
Class List
Click for more info and example uses
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The Object Diagrams

• Notoriously vast pdf UML diagrams. Can get to
  them via the Object Model Diagrams tree in the
  Help or in Arcs DeveloperKit/Diagrams/
  directory.
• Best to open the AllDesktopOMDs.pdf diagram and
  use Ctrl-F to search for an object class.

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Understanding UML

• http//edndoc.esri.com/arcobjects/8.3/
• ArcObjects online gt Object Models Diagrams gt How
  to read

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Summary

• Get the Applications Document.
• Get the Maps from it.
• Pick the one you want or loop through them.
• Get a Layer from the Map, or Loop through all of
  them.
• Generate an Attribute table and use Rows / Fields
  to get data.
• Or use the Layers search routine to search for
  Features.

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Next Lecture

• Editing data, running commands.
• VB.Net, ActiveX/Com and ModelBuilder.
• Practical
• Data manipulation