need help with listview items with images

[mia]

hi i created project to add items to listview with image and exchange items every thing working fine but sadly sometimes while exchange items image object gets nil any idea what iam doing wrong

here is my full project source

to test compile the project then run it and add string first then add item then add string again the click on exchange and see whats happend

[mia]

5 downloads no single answer

[mrmarman]

Hi mia.

I have a look at your code.
If you check any object "if exists" by "If Assigned" keyword you must "nil" them after "free" command.

You must make object UnAssigned after free by equaling to NIL.

Kod: Tümünü seç

    listms.Free;
    listms := Nil;

[mia]

i freed the memory stream and sit it to nil byt still my image object gets nil after exchange to be more specific

this parameter gets nil after exchange some times look at doUpdateVisual and UpdateVisual parameter comments

Kod: Tümünü seç

procedure TURLDownload.DoUpdateVisual;
begin
  if Assigned(FOnUpdateVisual) then
    FOnUpdateVisual(Self, FUserData// this one is nil, FGif// is nil);
end;


procedure TForm1.UpdateVisual(Sender: TObject; AUserData: Pointer;// this one is nil var AImage: TGifImage // this one is nil );
var
 Item: TListItem;
i : integer;
begin
 Item := TListItem(AUserData);

  if ListView1.Items.IndexOf(Item) = -1 then
    Exit;

  Item.Data := AImage;
  AImage := nil;

if recorder = True then
      begin
       for i := 0 to ListView1.Items.Count-1
     do if ListView1.Items[i].SubItems[3] = IntToStr(UniqueID)
     then
     begin
     ExchangeItems(ListView1, I, 0);
     ListView1.Invalidate;
     end;
   end;
end;  

//download code 

procedure TURLDownload.Execute;
var
  aMs: TMemoryStream;
  hSession     : HINTERNET;
  hService     : HINTERNET;
  lpBuffer     : array[0..1023] of Byte;
  dwBytesRead  : DWORD;
  dwBytesAvail : DWORD;
  dwTimeOut    : DWORD;
begin
  FGif := TGifImage.Create;
  try
  aMs := TMemoryStream.Create;
  hSession := InternetOpen('anyname', INTERNET_OPEN_TYPE_PRECONFIG, nil, nil, 0);
  if not Assigned(hSession) then Exit;
    try
      hService := InternetOpenUrl(hSession, PChar(FUrl), nil, 0, 0, 0);
    if hService = nil then
      Exit;
      try
      dwTimeOut := 60000;
      InternetSetOption(hService, INTERNET_OPTION_RECEIVE_TIMEOUT, @dwTimeOut, SizeOf(dwTimeOut));
      if InternetQueryDataAvailable(hService, dwBytesAvail, 0, 0) then
      repeat
      if not InternetReadFile(hService, @lpBuffer[0], SizeOf(lpBuffer), dwBytesRead) then
      Break;
      if dwBytesRead <> 0 then
      aMs.WriteBuffer(lpBuffer[0], dwBytesRead);
      until dwBytesRead = 0;
      finally
       InternetCloseHandle(hService);
      end;
      aMs.Position := 0;
      FGif.LoadFromStream(aMs);
      FGif.Transparent := True;
    finally
      aMs.Free;
      InternetCloseHandle(hSession);
    end;
    if Assigned(FOnUpdateVisual) then
    begin
      Synchronize(DoUpdateVisual);
    end;
  finally
    FGif.Free;
  end;
end;

[mrmarman]

I only looked for where the code stucked. If you press second time the button it was giving access violation error. That problem was the if block which checks freeed "listms" is assigned.

That object sits the nil but stays assigned. The difference is how to look at this.

If you free an object then you must check "is nil" but must not use "is assigned" until equal to nil.

Some of free command do the object unassigned but tmemorystream needs both free and nil.

Make look for (3) of double slash after lines the code below.

Kod: Tümünü seç

procedure TForm1.AdditemClick(Sender: TObject);
var
I : integer;
Line: string;
strName, strUniqueID, icon : String;
strSelectedUID : String;
Sl : Tstringlist;
begin
  if ListView1.Selected <> nil
      then strSelectedUID := Listview1.Selected.SubItems[3]
      else strSelectedUID := '';
    listview1.Items.BeginUpdate;
    try
    ListView1.Items.Clear;
finally
    listview1.Items.EndUpdate;
  end;
    if Assigned(listms) then
     //SL := TStringList.Create; //removed from here...
    begin
      SL := TStringList.Create; // Moved to here
      try
        Sl.LoadFromStream(listms);
        for I := 0 to SL.Count -1  do
        begin
            Line := SL.Strings[I];
            parselist(Line, strName, strUniqueID, icon);
            boolblink := True;
           Add_Item( strName, ListView1, icon, boolblink, strUniqueID, Status);
        end;
      finally
       Sl.Free
      end;
      listms.Free;
      listms := Nil; // append by ARMAN

    if strSelectedUID <> '' then
      begin
        for i := 0 to ListView1.Items.Count-1
          do if ListView1.Items[i].SubItems[3] = strSelectedUID
            then Listview1.Items[i].Selected := True;
      end;
    end;
end;

The whole code needs to trace more. I will check it out in day time.

[mia]

yes the code is really complicated i spend days to discover what happened still don't found it yet . i will wait when you have time