Property Get problem

[Ken Elvehjem]

Hi,

I'm trying my hand at COM programming. The examples seem to work fine, but I'm having a little trouble with Property Get statements in the real world.

I am trying to open (and see some properties of) an ESRI ShapeFile using the OCX provided by the OpenSource MapWindow project. The COM browser looked it over, liked it, and generated a .INC file for the OCX.

The following is an excerpt from the .INC file:

    INTERFACE IShapefile $IID_MapWinGIS_IShapefile
    INHERIT IDISPATCH

    PROPERTY GET NumShapes <1> () AS LONG
    PROPERTY GET NumFields <2> () AS LONG
    PROPERTY GET Extents <3> () AS IExtents
    PROPERTY GET ShapefileType <4> () AS LONG
    PROPERTY GET Shape <5> (BYVAL ShapeIndex AS LONG) AS IShape
    PROPERTY GET EditingShapes <6> () AS INTEGER
    PROPERTY GET LastErrorCode <7> () AS LONG
    PROPERTY GET CdlgFilter <8> () AS STRING
    PROPERTY GET GlobalCallback <9> () AS ICallback
    PROPERTY SET GlobalCallback <9> (BYVAL pVal AS ICallback)
    PROPERTY GET Key <10> () AS STRING
    PROPERTY SET Key <10> (BYVAL pVal AS STRING)
    METHOD OPEN <11> (BYVAL ShapefileName AS STRING, OPT BYVAL cBack AS ICallback) AS INTEGER
    METHOD CreateNew <12> (BYVAL ShapefileName AS STRING, BYVAL ShapefileType AS LONG) AS INTEGER
    METHOD SaveAs <13> (BYVAL ShapefileName AS STRING, OPT BYVAL cBack AS ICallback) AS INTEGER
    METHOD CLOSE <14> () AS INTEGER

I was overjoyed when the "OPEN" method worked in my little piece of code that follows. Then, I wanted to view one of the properties of the shapefile. I must have missed something because the "ShapeCount =" line near the end of the code below returns an error at the .ShapeCount item saying that a method or property is expected.

#COMPILE EXE
#DIM ALL
#INCLUDE "MapWinInc.inc"

GLOBAL ShapeName AS STRING

DECLARE FUNCTION OpenShp() AS INTEGER

FUNCTION PBMAIN () AS LONG

    'MSGBOX "Got Here"
     IF COMMAND$ = "" THEN
         shapename = "c:\newmaps\B-L Little 08 Harvest.shp"
     ELSE
         ShapeName = COMMAND$
     END IF

    openshape

END FUNCTION

FUNCTION OpenShape() AS INTEGER

    LOCAL DispVar AS DISPATCH
    LOCAL ShapeCount AS LONG
    
    LOCAL mShapeCallBack AS ICallBack

    LET DispVar = NEWCOM "IShapefile"

    OBJECT CALL DispVar.open(ShapeName, mShapeCallBack)

    ShapeCount = DispVar.ShapeCount              'Error shows up in this line

    FUNCTION = 1

END FUNCTION

I'm sure I am missing something, but at this point, I can't figure out what it might be...

Some helpful comments would sure be appreciated!

Ken

[Steve Rossell]

Hi Ken,

Try using the direct v-table methods or use OBJECT GET.

Function PBMain () As Long
  Local O As IShapefile
  Local ShapeCount As Long
  Local mShapeCallBack As ICallBack

  o = NewCom $PROGID ' or use CLSID
  o.Open(ShapeName, mSShapeCallback)

  ShapeCount = o.ShapeCount

  Function = 1
End Function

[José Roca]

You're mixing apples with oranges, i.e. you have generated an interface definition for direct interface calls use and then you are using OBJECT CALL for the Open method, and then a direct interface call for the ShapeCount property but with a variable dimmed as DISPATCH instead of an interface.

Try the following:

LOCAL DispVar AS IShapeFile
LOCAL ShapeCount AS LONG

DispVar = NEWCOM "IShapefile"
DispVar.open(UCODE$(ShapeName), NOTHING)
ShapeCount = DispVar.ShapeCount

[Ken Elvehjem]

Property Get problem

Steve & José,

Thank you for your responses.

I can see that I *should* have attached my BAS and INC files....

Both of your proposed solutions seem to give an error.

José, I understand what you mean about the Apples and Oranges, but I somehow keep missing what my mistake *is*.

Please note the attached files.

Sincerely,

Ken

[José Roca]

I don't see any property called ShapeCount in the MapWinInc include file. Probably NumShapes is what you have to use.

[Ken Elvehjem]

Property Get problem

OK, fixed *that*.

Now, when debugging, I get the error that follows when I get to this line:

DispVar.open(UCODE$(ShapeName), NOTHING)

I can't tell why this is a memory access violation...

Ken

Component Files:
----------------
C:\POLYEX~1\PolyExtract.bas
C:\POLYEXTRACT\MAPWININC.INC
==============================
Compile succeeded at 2:24:48 PM on 7/9/2009

Begin Debug at 2:24:48 PM on 7/9/2009
Exception: Memory Access Violation
Program tried to read or write an invalid memory address
End Debug at 2:24:52 PM on 7/9/2009

[José Roca]

Check if DispVar contains a valid reference, e.g.

IF ISNOTHING(DispVar) THEN EXIT FUNCTION   ' Not a valid object

You are using DispVar = NEWCOM "IShapefile" to create the object, yet there is no such a ProgID in the include file (in fact, there is not any ProgID).

Probably you will have to use:

DispVar = NEWCOM CLSID $CLSID_MapWinGIS_Shapefile

[Ken Elvehjem]

José

That last worked just great.

I can now have it returning the rest of the info re: the shapefile.

Thanks once again for the solution to this problem!

Ken

[Ken Elvehjem]

A few days later...

I am trying to use one of the Methods(SelectShapes) to select individual shape items from within the ShapeFile.

I have a Variant variable named Result() dimensioned as a LOCAL, and redimensioned to "some reasonable value". (I used 250)

When I use that variable in the Method call, however, I am told it is "Undeclared" (error 519) on compiling.

    LOCAL Result() AS VARIANT
    LOCAL xxmin, yymin, xxmax, yymax AS DOUBLE
    REDIM Result(250)
.
.
.
    xxMin = -91.85
    yyMin =  42.62
    xxMax = -91.80
    yyMax =  42.63
    Extents1.SetBounds(xxmin, yymin, 0, xxmax, yymax, 0)
    
    DispVar.SelectShapes(extents1, 0.0, %INTERSECTION, Result )

The include file I am using was posted to this thread earlier.

José, I read some of your posts and Michael M's on a previous thread :

http://www.powerbasic.com/support/pbforums/showthread.php?t=40757

I suspect that this is "sort of" the same kind of problem, but I can't see it from here.

Any comments would be greatly appreciated.

Ken

[José Roca]

When I use that variable in the Method call, however, I am told it is "Undeclared" (error 519) on compiling.

Of course. The parameter is a variant and you are trying to pass an array of variants. Just pass a variant.

A different matter is if that variant must hold a reference to an array of something or not, or if the method just wants a variant and will return a safearray int it, or whatever. Hard to say without having documentation and without being able to test.

[Ken Elvehjem]

OK, I understand that...

Fixed it, and it compiles. It crashes when I try to run it.

Used debug to run it...

Then it stops on that line and sez:

Begin Debug at 11:49:26 AM on 7/17/2009
Exception: Memory Access Violation
Program tried to read or write an invalid memory address
End Debug at 11:49:33 AM on 7/17/2009

Here's where that method is explained...

http://www.mapwindow.org/wiki/index.php/MapWinGIS:Shapefile_SelectShapes

I notice that the VB.Net reference shows it as an integer.

Ken

[José Roca]

Your link only shows how to call the method using VB.NET or VB6, but doesn't explain what kind of variant wants. I have no idea of what VB does under the hood.

[José Roca]

Check also if extents1 is a valid object. Are you creating an instance of it? You aren't showing any code.

[Ken Elvehjem]

José,

Sorry 'bout that.

I *did* declare it... see code below. That doesn't mean it's valid...;>)

The theory being that a shapefile containing individual shapes (points, lines, polygons, etc.) in an X,Y,Z format can be queried with the SelectShapes method.

Being still new at this, I find the .INC file a little intimidating. Nevertheless, I have tried to get it to select these shapes for me, based on a bounding rectangle. Part of my problem is that the "extents" shows up as a "class" in the .inc file.

This means I am not sure that I am specifying those extents correctly.

I am including my code here, and attaching the .inc file.

Ken

#COMPILE EXE
#DIM ALL
#INCLUDE "MapWinInc.inc"

GLOBAL ShapeName AS STRING

DECLARE FUNCTION OpenShp() AS INTEGER

FUNCTION PBMAIN () AS LONG

    LOCAL d$

    'MSGBOX "Got Here"
     IF COMMAND$ = "" THEN
         'shapename = "c:\newmaps\B-L Little 08 Harvest.shp"
         d$ = DIR$("c:\MissProfit\Data\*.shp")
         DO WHILE LEN(d$)
             ShapeName = "c:\MissProfit\Data\" & d$
             OpenShape
             d$ = DIR$
         LOOP
     ELSE
         ShapeName = COMMAND$
         OpenShape
     END IF

'    openshape

END FUNCTION

FUNCTION OpenShape() AS INTEGER

    LOCAL DispVar AS IShapeFile
    LOCAL DBVar AS ITable
    LOCAL CSVName AS STRING
    LOCAL ShapeCount, ShapeType, NumFields AS LONG
    LOCAL NumPoints AS LONG
    LOCAL PointAvx, PointAvy AS DOUBLE
    LOCAL Extents AS IExtents
    LOCAL Extents1 AS IExtents
    
    LOCAL OneShape AS Ishape, OnePoint AS IPoint, OneTable AS ITable

    LOCAL DBF AS STRING, DBFRows AS LONG, DBFFields AS LONG

    LOCAL a, b AS LONG
    LOCAL t AS INTEGER
    LOCAL Zval AS DOUBLE, ZV AS VARIANT, success AS LONG

    LOCAL Result AS VARIANT
    LOCAL xxmin, yymin, xxmax, yymax AS DOUBLE
    
    
    DBF = UCASE$(ShapeName)
    REPLACE ".SHP" WITH ".DBF" IN DBF

    CSVName = UCASE$(ShapeName)
    REPLACE ".SHP" WITH ".CSV" IN CSVName


    'DispVar = NEWCOM "IShapefile"
    DispVar = NEWCOM CLSID $CLSID_MapWinGIS_Shapefile
'    IF ISNOTHING(DispVar) THEN MSGBOX "It's nothing"

    DispVar.open(UCODE$(ShapeName), NOTHING)
'    IF ISNOTHING(DispVar) THEN MSGBOX "It's nothing"

     ShapeCount = DispVar.NumShapes
   ' MSGBOX "Number of Shapes: " & STR$(ShapeCount)
    ShapeType = DispVar.ShapeFileType
   'MSGBOX "Type of Shape: " & STR$(ShapeType)
     NumFields = DispVar.NumFields
    'MSGBOX "Number of Fields: " & STR$(NumFields)
     Extents = DispVar.Extents
    'MSGBOX STR$(Extents.xMin) & "   " & STR$(Extents.xMax) & $CR & $LF &  STR$(Extents.yMin)  & "   " & STR$(Extents.yMax)


'DBF Stuff *=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
    DBVar = NEWCOM CLSID $CLSID_MapWinGIS_Table
    DBVar.open(UCODE$(DBF), NOTHING)
    DBFRows = DBVar.NumRows
    DBFFields = DBVar.NumFields
    'Msgbox str$(DBFRows) & STR$(DBFFields)
'DBF Stuff *=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=


'Select Shapes Stuff *=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
'    METHOD SetBounds <1> (BYVAL xMin AS DOUBLE, BYVAL yMin AS DOUBLE, BYVAL zMin AS DOUBLE, BYVAL xMax AS DOUBLE, BYVAL yMax _
'        AS DOUBLE, BYVAL zMax AS DOUBLE)

'    METHOD SelectShapes <18> (BYVAL BoundBox AS IExtents, OPT BYVAL Tolerance AS DOUBLE, OPT BYVAL SelectMode AS LONG, OPT _
'        BYREF IN result AS VARIANT) AS INTEGER

    xxMin = -91.85
    yyMin =  42.62
    xxMax = -91.80
    yyMax =  42.63
    Extents1.SetBounds(xxmin, yymin, 0, xxmax, yymax, 0)
    
    success = DispVar.SelectShapes(extents1, 0, %INTERSECTION, BYREF Result )
    

'Select Shapes Stuff *=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=

GOTO JumpOut

    t = FREEFILE
    OPEN CSVName FOR OUTPUT AS #t

    FOR a = 0 TO ShapeCount - 1
        OneShape = DispVar.Shape(a)
        NumPoints = OneShape.numpoints
        'if a < 5 then MSGBOX "Vertices in Shape "  & str$(a) & "=" & str$(OneShape.NumPoints)
        PointAVx = 0
        PointAVy = 0
        'print #t, a, NumPoints, " Points"
        FOR b = 0 TO NumPoints - 1
            OnePoint = OneShape.Point(b)
            PointAVx = PointAVx + onepoint.x
            PointAVy = PointAVy + onepoint.y
            'PRINT #t, OnePoint.x, onepoint.y, PointAVx, PointAVy

        NEXT b
        pointAVx = PointAVx / NumPoints
        pointAVy = PointAVy / NumPoints

        ZV = DBVar.CellValue(3, a)
        ZVal = VARIANT#(ZV)
       ' if a < 10 then msgbox str$(ZVal)

        PRINT #t, PointAVx; ","; PointAVy; ","; ZVal   ' "  == Averages"

        'IF a < 5 THEN MSGBOX STR$(OnePoint.x) & "   " & STR$(OnePoint.y)
        'IF a < 5 THEN MSGBOX STR$(PointAVx) & "   " & STR$(PointAVy)


    NEXT a
    CLOSE #t
JumpOut:


    FUNCTION = 1

END FUNCTION

[José Roca]

I *did* declare it... see code below. That doesn't mean it's valid...;>)

I mean if it contains a valid reference. Just declaring it, initializes it with a NULL reference, and calling a method using a null object variable only leads to a crash.

You will have to use:

exents1 = NEWCOM CLSID $CLSID_MapWinGIS_Extents

[José Roca]

Part of my problem is that the "extents" shows up as a "class" in the .inc file.

What class? I see it as an interface:

' Interface Name  : IExtents
' Description     : IExtents Interface
' ClassID         : $CLSID_MapWinGIS_Extents
Interface IExtents $IID_MapWinGIS_IExtents
    Inherit IDispatch

    Method SetBounds <1> (Byval xMin As Double, Byval yMin As Double, Byval zMin As Double, Byval xMax As Double, Byval yMax _
        As Double, Byval zMax As Double)
    Method GetBounds <2> (ByRef xMin As Double, ByRef yMin As Double, ByRef zMin As Double, ByRef xMax As Double, ByRef yMax _
        As Double, ByRef zMax As Double)
    Property Get xMin <3> () As Double
    Property Get xMax <4> () As Double
    Property Get yMin <5> () As Double
    Property Get yMax <6> () As Double
    Property Get zMin <7> () As Double
    Property Get zMax <8> () As Double
    Property Get mMin <9> () As Double
    Property Get mMax <10> () As Double
    Method GetMeasureBounds <11> (ByRef mMin As Double, ByRef mMax As Double)
    Method SetMeasureBounds <12> (Byval mMin As Double, Byval mMax As Double)
End Interface

[Ken Elvehjem]

Worked Great!

So...

for this "extents1" object to be valid, I have to:

declare it: LOCAL Extents1 AS IExtents
load it: Extents1 = NEWCOM CLSID $CLSID_MapWinGIS_Extents
Then use it: Extents1.SetBounds(xxmin, yymin, 0, xxmax, yymax, 0)

Right?

Now,

According to the debug facility, the variable "Result" in the SelectShapes Method returns a "Safe Array" item.

How do I access the elements of that array in my program?

Ken

[José Roca]

Try this:

DIM rgResult(0) AS LONG
rgResult() = Result

If you are lucky, you will get an array of long values.

[Ken Elvehjem]

José

That did the trick. I can now select the appropriate polygons from a group of 25,000 polygons in about zero seconds!

I tried to do similar stuff before that OCX was available, and almost had a nervous breakdown. In fact, I wore out keyboards entering line after line of glue and support code.

Now, in 30 - 40 lines of code, it's all practically done for me.

As Little Orphan Annie said, "I really think I'm gonna like it here!"

Thanks for all your help!

Ken