Hi list,

(FPC 2.6.0 or trunk)

Been fiddling a bit too long and strongly suspect PEBKAC/PICNIC (and my seemingly perennial refusal to adapt to Object Pascal's way of dealing with object references).

Thanks for your suggestions!

See the ===> marks below

var
  CurrentPage: integer;
  RequestResult: THttpResult;
  CommJSON: TJSONObject;
begin
  result:=INVALIDID;
  CommJSON:=TJSONObject.Create;
  try
    try
// do an HTTP request and get a JSONData back.
//
RequestResult:=HttpRequestWithData(CommJSON,FCGIURL+'document/',rmPost);
      if RequestResult.Code200 then
      begin
//snip error handling
      end
      else
      begin
//===> the line below works - so CommJSON is a valid object, right?
        if Assigned(CommJSON) then
        begin
//====> however, the next line gives a runerror(210): no vmt found
          if (CommJSON.JSONType=jtObject) then
          begin
            if (CommJSON.IndexOfName('documentid',false)>-1) then
              result:=CommJSON.Integers['documentid'];
          end;
        end;
      end;
I'm not confident about
function HttpRequestWithData(AData: TJSONData; const AUrl: string;
  const AMethod: TRequestMethod; const AContentType: string): THttpResult;
...
      FreeAndNil(AData);
      VData.Position := 0;
      VParser := TJSONParser.Create(VData);
      try
        try
          AData := VParser.Parse;
//====> so it destroys the object passed to it and recreates it
//====> but AData.JSONType does seem to be JSONObject...

It is assigned, but not necessarily valid. If you freed CommJSON but did not nil it, it is still'assigned'.

Ehm. This must be

  function HttpRequestWithData(OUT AData: TJSONData; const AUrl: string;
   const AMethod: TRequestMethod; const AContentType: string): THttpResult;

Because you are passing BACK a reference!

Michael.

On 12-3-2013 11:44, Michael Van Canneyt wrote:

Thanks for the help, Michael.

Understood. Then it has a pointer pointing to whatever (probably the object's former memory location).

Sorry. What I hadn't attached is the first part where the request is
built up:
    if Assigned(AData) then
    begin
      VHttp.RequestBody := TMemoryStream.Create;
      VJSON := AData.AsJSON;
      VHttp.RequestBody.Write(Pointer(VJSON)^, Length(VJSON));
      VHttp.RequestBody.Position := 0;
    end;

... changing the parameter to var...

function HttpRequestWithData(var AData: TJSONData; const AUrl: string;
  const AMethod: TRequestMethod; const AContentType: string): THttpResult;

... and changing the calling objects from TJSONObject to TJSONData seemed to do the trick.

Thanks a lot.

Yes, but as per your code: you free and rebuild:

       FreeAndNil(AData);
       VData.Position := 0;

-> so you change the parameter, and thus you need a var/out

Anyway, glad it is fixed.

Michael.