How to Use Polylines at Runtime

VCL TMS VCL WebGMaps
1

I am getting the error message below when exiting my program if I have more than one Polyline on the map.



"Project utilmarker.exe raised exception class EInvalidPointer with message 'Invalid pointer operation'.



I went back to the basics from your sample code and came up with this to show my problem using only 2 Polylines...



procedure TMainForm.AddPolylinesToMap;

var

Icons: TSymbols;

pi: TPathItem;

aPath: TPath;



begin

Icons := TSymbols.Create;

aPath := TPath.Create;



pi := aPath.add;

pi.Latitude := 39.58108;

pi.Longitude := -105.63535;



pi := aPath.add;

pi.Latitude := 40.315939;

pi.Longitude := -105.440630;



pi := aPath.add;

pi.Latitude := 43.785890;

pi.Longitude := -101.90175;



MyMap.Polylines.Add(True, False, False, Icons, aPath, clBlue, 100, 10, True, 0);



aPath.Clear;



pi := aPath.add;

pi.Latitude := 49.58108;

pi.Longitude := -115.63535;



pi := aPath.add;

pi.Latitude := 50.315939;

pi.Longitude := -115.440630;



pi := aPath.add;

pi.Latitude := 53.785890;

pi.Longitude := -111.90175;



MyMap.Polylines.Add(True, False, False, Icons, aPath, clBlue, 100, 10, True, 0);

end;



For testing purposes trying to find what is causing my problem I have did these tests



1) call MyMap.Polylines.Clear before adding the second Polyline, when I exit I do not get the error (has something to do with reusing the variables icons or apath?)



2) create a second set of variables (Icons2, pi2 and aPath2). Substitute those variables for the second Polyline and I do not get the error.

Second Polyline would be

MyMap.Polylines.Add(True, False, False, Icons2, aPath2, clBlue, 100, 10, True, 0); (no error on exit)



3) if I re-use either Icons or aPath variables in the second Polyline I get the error:

MyMap.Polylines.Add(True, False, False, Icons, aPath2, clBlue, 100, 10, True, 0); (error on exit)

or

MyMap.Polylines.Add(True, False, False, Icons2, aPath, clBlue, 100, 10, True, 0); (error on exit)



What am I doing wrong to programmatically add multiple Polylines at runtime?

2

Hi,


Can you please try to do a create instead of a clear on the Path and Icons?

Example:
procedure TMainForm.AddPolylinesToMap; 
var 
Icons: TSymbols; 
pi: TPathItem; 
aPath: TPath; 

begin 
Icons := TSymbols.Create; 
aPath := TPath.Create; 

pi := aPath.add; 
pi.Latitude := 39.58108; 
pi.Longitude := -105.63535; 

pi := aPath.add; 
pi.Latitude := 40.315939; 
pi.Longitude := -105.440630; 

pi := aPath.add; 
pi.Latitude := 43.785890; 
pi.Longitude := -101.90175; 

MyMap.Polylines.Add(True, False, False, Icons, aPath, clBlue, 100, 10, True, 0); 

//aPath.Clear; 
aPath := TPath.Create;
Icons := TSymbols.Create; 

pi := aPath.add; 
pi.Latitude := 49.58108; 
pi.Longitude := -115.63535; 

pi := aPath.add; 
pi.Latitude := 50.315939; 
pi.Longitude := -115.440630; 

pi := aPath.add; 
pi.Latitude := 53.785890; 
pi.Longitude := -111.90175; 

MyMap.Polylines.Add(True, False, False, Icons, aPath, clBlue, 100, 10, True, 0); 
end; 
3

That solved my problem! I had previously tried doing creates on them for each Polyline iteration in my original code but apparently I had mistakenly placed them in the wrong place in my loop. Thanks!!!