(SOLVED) Detect kind of file using DragAndDrop

[AsleyCruz]

Hi guys,
My would like my application accept txt files only on drag/drop files on the form.

If the file that is being draging is .txt, I would like to use the cursor "accept-file"
if not, use the cursor "forbidden-file". See attached image.

How can I detect the kind of file?

[lucamar]

The OnDropFiles handler receives a list of the files dropped so all you need to do is to check the extensions or, probably better, whether they are in fact text files:

Code: Pascal  [Select][+][-]

1. procedure TMainForm.FormDropFiles(Sender: TObject;
2.   const FileNames: array of String);
3. var
4.   AFileName: String;
5. begin
6.   for AFileName in FileNames do
7.     if Lowercase(ExtractFileExtension(AFileName)) = '.txt' then begin
8.       {Do whatever}
9.     end;
10.     {Alternatively, using LazFileUtils:
11.     if FileIsText(AFileName) then begin
12.       // Do whatever
13.     end;
14.     }
15. end;

[ASerge]

In Windows, OnDropFiles is triggered only when files are already dropped as a result of processing the WM_DROPFILES message. From MSDN "Avoid using Windows 3.1 targets or the WM_DROPFILES message, if possible".
In your case, it is also better to explicitly use the IDataObject interface to respond dragging files over the form. For the example of how exactly, I have attached a small unit. And an example of its use is as follows:

Code: Pascal  [Select][+][-]

1. type
2.   TForm1 = class(TForm)
3.     Memo1: TMemo;
4.     procedure FormCreate(Sender: TObject);
5.     procedure FormDestroy(Sender: TObject);
6.   private
7.     function AcceptFiles(Files: TStrings): Boolean;
8.     procedure FilesWasDropped(Files: TStrings);
9.   end;
10.  
11. var
12.   Form1: TForm1;
13.  
14. implementation
15.  
16. uses uDropTarget;
17.  
18. {$R *.lfm}
19.  
20. function TForm1.AcceptFiles(Files: TStrings): Boolean;
21. var
22.   FileName: string;
23. begin
24.   Result := False;
25.   for FileName in Files do
26.     Result := Result or SameFileName(ExtractFileExt(FileName), '.txt');
27. end;
28.  
29. procedure TForm1.FilesWasDropped(Files: TStrings);
30. begin
31.   Memo1.Text := Files.Text;
32. end;
33.  
34. procedure TForm1.FormCreate(Sender: TObject);
35. begin
36.   RegisterDropTarget(Handle, @AcceptFiles, @FilesWasDropped);
37. end;
38.  
39. procedure TForm1.FormDestroy(Sender: TObject);
40. begin
41.   UnregisterDropTarget(Handle);
42. end;

[jamie]

Thank you very much for dropping your example here.

I have in the past implemented the IdragDrop handler but found that it has some issues of its own, mainly resource issues..

  I will look at your example to see if there is anything you are doing differently..

 

[AsleyCruz]

In Windows, OnDropFiles is triggered only when files are already dropped as a result of processing the WM_DROPFILES message. From MSDN "Avoid using Windows 3.1 targets or the WM_DROPFILES message, if possible".
In your case, it is also better to explicitly use the IDataObject interface to respond dragging files over the form. For the example of how exactly, I have attached a small unit. And an example of its use is as follows:

Code: Pascal  [Select][+][-]

1.  

Thanks ASerge, works like a charm.
My application only accepts .ico and .exe files. You can see how it works in the gif attached.

Thanks again.