Author: Tomas Rutkauskas

Does anyone have an example of using CopyFileEx with a CopyProgressRoutine? I have 
created a function that takes the same parameters as the CopyProgressRoutine, but 
when I pass it using @ or Addr() I get a Variable Required error message.

Answer:

Let's assume you call CopyFileEx and want the callback to update a progress bar. 
The callback cannot be an objects method but you can use the lpData parameter of 
CopyFileEx to pass any kind of data to the callback, e.g. a form reference. So, if 
you want to serve a progress form in the callback that would look like this 
(untested !):
1   
2   type
3     TProgressForm = class(TForm)
4       AbortButton: TButton;
5       ProgressBar: TProgressBar;
6       procedure AbortButtonClick(Sender: TObject);
7     private
8       { Private declarations }
9     public
10      { Public declarations }
11      FCancel: BOOL;
12    end;
13    {form has fsStayOnTop formstyle!}
14  
15  implementation
16  
17  {$R *.DFM}
18  
19  procedure TProgressForm.AbortButtonClick(Sender: TObject);
20  begin
21    FCancel := True;
22  end;
23  
24  {Note: could use int64 instead of COMP, but that would make this D4 specific}
25  
26  function CopyCallback(TotalFileSize, TotalBytesTransferred, StreamSize,
27    StreamBytesTransferred: COMP; dwStreamNumber, dwCallbackReason: DWORD;
28    hSourceFile, hDestinationFile: THandle; progressform: TProgressForm): DWORD; 
29  stdcall;
30  var
31    newpos: Integer;
32  begin
33    Result := PROCESS_CONTINUE;
34    if dwCallbackReason = CALLBACK_CHUNK_FINISHED then
35    begin
36      newpos := Round(TotalBytesTransferred / TotalFileSize * 100);
37      with progressform.Progressbar do
38        if newpos <> Position then
39          Position := newpos;
40      Application.ProcessMessages;
41    end;
42  end;
43  
44  function DoFilecopy(const source, target: string): Boolean;
45  var
46    progressform: TProgressForm;
47  begin
48    progressform := TProgressform.Create;
49    try
50      progressform.Show;
51      Application.ProcessMessages;
52      Result := CopyFileEx(PChar(source), PChar(target), @CopyCallback,
53  		 Pointer(progressform), @progressform.FCancel, 0);
54    finally
55      progressform.Hide;
56      progressform.free;
57    end;
58  end;