firemonkey threading on android show a black page

Question

i used a httpd to request some data from internet

function requestToServer(lParamList: TStringList) : string;
var
  userDataString : string;
  lHTTP: TIdHTTP;
  serverResponce : string;
  aobj: ISuperObject;
begin
application.ProcessMessages;
  TThread.CreateAnonymousThread(
    procedure
    begin
        lHTTP := TIdHTTP.Create(nil);
        try
          serverResponce := lHTTP.Post('http://domain.com/mjson.php', lParamList);
          application.ProcessMessages;
          aobj:= SO(serverResponce);
          try
             X := aobj['dta'].AsArray;
          Except
            form2.Memo1.Lines.Add('errr');
          end;
            if aobj['result'].AsString = 'lr_102' then
            begin
             form2.Label3.Text:='Saved token expired.';
             form2.Rectangle2.Visible:=true;
            end
            else if aobj['result'].AsString = 'lr_103' then
            begin
             form2.Label3.Text:='Auto login.';
             //load device data
             form2.allDeviceListData := X;
             form2.Hide;
             form1.show;
            end;
           // globalReachedServer:=true;
        finally
          lHTTP.Free;
          lParamList.Free;
        end;

      TThread.Synchronize(nil,
        procedure
        begin

        end);
    end
  ).Start();
end;

but after reach this function the application show a black page and dont do anything until manually close

how can i do a web request at the background and with out hanging on fire-monkey !? what a bout using REST is it better to access web service's?

Answer 1

Your code is not thread-safe. Your thread is directly accessing UI controls without synchronizing with the main UI thread. That alone can cause problems.

Also, all of the variables declared in the var section of requestToServer() should be moved into the var section of the anonymous procedure instead, since requestToServer() does not use them, so they can be completely local to the thread instead. The only thing the anonymous procedure should be capturing is the lParamList content.

Try something more like this:

function requestToServer(lParamList: TStringList) : string;
var
  Params: TStringList;
  Thread: TThread;
begin
  Params := TStringList.Create;
  try
    Params.Assign(lParamList);
  except
    Params.Free;
    raise;
  end;
  TThread.CreateAnonymousThread(
    procedure
    var
      lHTTP: TIdHTTP;
      serverResponce : string;
      aObj: ISuperObject;
    begin
      try
        try
          lHTTP := TIdHTTP.Create(nil);
          try
            serverResponce := lHTTP.Post('http://domain.com/mjson.php', lParamList);
            aObj := SO(serverResponce);
            if aObj['result'].AsString = 'lr_102' then
            begin
              TThread.Queue(nil,
                procedure
                begin
                  form2.Label3.Text := 'Saved token expired.';
                  form2.Rectangle2.Visible := true;
                end
              );
            end
            else if aObj['result'].AsString = 'lr_103' then
            begin
              X := aObj['dta'].AsArray;
              TThread.Queue(nil,
                procedure
                begin
                  form2.Label3.Text := 'Auto login.';
                  //load device data
                  form2.allDeviceListData := X;
                  form2.Hide;
                  form1.show;
                end
              );
            end;
            // globalReachedServer := true;
          finally
            lHTTP.Free;
          end;
        finally
          Params.Free;
        end;
      except
        TThread.Queue(nil,
          procedure
          begin
            form2.Memo1.Lines.Add('errr');
          end
        );
      end;
    end
  ).Start;
end;