Create multiple tasks without freezing the interface

[DarkDucke 2]

Hello, I need to create a task for each row of a TSgringGrid, this task will take content from a web page, and update the data in a cell.

I tried as follows:

 

procedure TForm1.BitBtn1Click(Sender: TObject);
var
 I, nCount : Integer;
begin
 I := 0;
 nCount := 0;
 
 for I := 1 to StringGrid.RowCount-1 do
   begin

    if StringGrid.Cells[0, I] <> 'done' then
      begin
	    inc(Q);
		if Q > 5 then
		  Break;
		
        Async(
         procedure
          begin
             Memo1.lines.add('I=' + I.ToString() + ' Q=' + Q.ToString());
             GetWebContent(I);
          end
        ).Await(
         procedure
          begin
             Memo1.lines.add('Done I=' + I.ToString() + ' Q=' + Q.ToString());
          end);

      end;
  end;
end;

 

But that doesn't work, the value of I is always the same, I can't get the position of the TStringGrid line.

How can I do this? Create 5 out of 5 tasks until all Grid lines have been queried.

 

This cannot freeze the user interface.

 

Thanks!!

[Lars Fosdal 1793]

 

Is it about the pitfalls of variable captures? The simplest solution to that is to simply divide and conquer.

Also - the queuing code you wrote, will only do five scrapings since you never descrement nCount  when a task completes, nor do you retry the loop until there are no lines not containing 'done'.

procedure TForm1.QueueScraping(I, Q: Integer);  
  Async(
    procedure
    begin
      Memo1.lines.add('I=' + I.ToString() + ' Q=' + Q.ToString());
      GetWebContent(I);
    end
  ).Await(
    procedure
    begin
       Memo1.lines.add('Done I=' + I.ToString() + ' Q=' + Q.ToString());
    end);
end;

procedure TForm1.BitBtn1Click(Sender: TObject);
var
  I, nCount : Integer;
begin
  I := 0;
  nCount := 0;
  for I := 1 to StringGrid.RowCount-1 
  do begin
    if StringGrid.Cells[0, I] <> 'done' 
    then begin
      inc(nCount);
      if nCount > 5 
       then Break;
      QueueScraping(I, nCount)
    end;
  end;
end;

 

[DarkDucke 2]

1 hour ago, Lars Fosdal said:

 

Is it about the pitfalls of variable captures? The simplest solution to that is to simply divide and conquer.

Also - the queuing code you wrote, will only do five scrapings since you never descrement nCount  when a task completes, nor do you retry the loop until there are no lines not containing 'done'.

procedure TForm1.QueueScraping(I, Q: Integer);  
  Async(
    procedure
    begin
      Memo1.lines.add('I=' + I.ToString() + ' Q=' + Q.ToString());
      GetWebContent(I);
    end
  ).Await(
    procedure
    begin
       Memo1.lines.add('Done I=' + I.ToString() + ' Q=' + Q.ToString());
    end);
end;

procedure TForm1.BitBtn1Click(Sender: TObject);
var
  I, nCount : Integer;
begin
  I := 0;
  nCount := 0;
  for I := 1 to StringGrid.RowCount-1 
  do begin
    if StringGrid.Cells[0, I] <> 'done' 
    then begin
      inc(nCount);
      if nCount > 5 
       then Break;
      QueueScraping(I, nCount)
    end;
  end;
end;

 

In fact, I forgot to report, this code is in a button, but stored in a timer that checks again every 5s

[Lars Fosdal 1793]

Did the refactor solve your "always same I" problem?

[DarkDucke 2]

It worked perfectly, thanks for the help!