[fpc-pascal] JSON & me - blind again?

[Michael Van Canneyt]

On Tue, 12 Mar 2013, Reinier Olislagers wrote:

> 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.Code<>200 then
>      begin
> //snip error handling
>      end
>      else
>      begin
> //===> the line below works - so CommJSON is a valid object, right?
>        if Assigned(CommJSON) then

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

>        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;

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.