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Borland C++ Builder control accept dropped files

Posted on 2001-08-22
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Last Modified: 2007-12-19
Borland C++ Builder control accept dropped files

Q:  How do you make a control accept a file which is dragged over it?
Example:   *.txt file is dropped onto an application and the file is opened by the application.

I would like to have an edit box accept a *.txt file which is dropped onto it.  In addition, I would like an image box accept a *.bmp file which is dropped onto it.

I do not need help with opening these file types.  What I need is how to have the control recognize that a file is being dropped, and how do I get the filename, path, etc.
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Question by:lirtua
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6 Comments
 
LVL 14

Expert Comment

by:AlexVirochovsky
ID: 6414848
To deal file dropping
on a form, you have to do the following:

1) in the header file of the form, initialize the handling of the
WM_DROPFILES message, specifying the handling funtion.
Example:

class TForm1 : public TForm
{
private:
void virtual __fastcall WMDropFiles(TWMDropFiles &message);
public:
__fastcall TForm1(TComponent* Owner);
BEGIN_MESSAGE_MAP
MESSAGE_HANDLER(WM_DROPFILES,TWMDropFiles,WMDropFiles);
END_MESSAGE_MAP (TForm);
};

2) in your source code insert the function which should handle the
file dropping. Example:

void __fastcall TForm1::WMDropFiles (TWMDropFiles &message)
{
...
}
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Author Comment

by:lirtua
ID: 6415030
The code you supplied compiles and the application runs.  However, when dragging a file over the application, the nodrop icon is displayed.

Also, I cannot find information about the struct TWMDropFiles although I see its definition in messages.hpp.

How do I get the filename & path?
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LVL 14

Expert Comment

by:AlexVirochovsky
ID: 6417339
>>How do I get the filename & path?

void __fastcall TForm1::WMDropFiles (TWMDropFiles &message)
 
{
 UINT FileCount = DragQueryFile((HDROP) Msg.Drop, 0xFFFFFFFF, NULL,
 0);
 AnsiString FileName;
 AnsiString FileExtension;
 
 int FileLength;
 for(UINT ii=0; ii < FileCount; ii++)
 {
   FileName.SetLength(MAX_PATH);
 FileLength = DragQueryFile((HDROP)Msg.Drop, ii,
 FileName.c_str(), FileName.Length());
 FileName.SetLength(FileLength);
 ProcessFile(FileLength) // <------ Whatever you want it to be...
 } // end for
 DragFinish((HDROP) Msg.Drop);
 }
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Author Comment

by:lirtua
ID: 6419434
Thank you for the information on this.  The code you have supplied is compiling without error.  I appreciate that.

I think were getting close.  However, the form still will not accept a dropped file.  When dragging a file over the form during runtime, the nodrop icon is displayed.

With this final detail, i believe all will be well in the file dropping realm.
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LVL 14

Accepted Solution

by:
AlexVirochovsky earned 50 total points
ID: 6421357
Sorry, I forget one think(very impotant)
void __fastcall TForm1::FormCreate(TObject *Sender)
{
  DragAcceptFiles(Form1-> Handle, true);
}
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Author Comment

by:lirtua
ID: 6423024
Fantastic Alex - thanks for the help!
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