Title: Drag and Drop Thread
Question: This demo shows how to perform a drag drop wich does not block the user interface during the copying of large files.
Answer:
{ Drag & Drop Thread
Copyright (c) 2000, 2001 by E.J.Molendijk
This class is a part of:
"Drag and Drop Component Suite" (http://www.melander.dk).
Explained:
When you create the thread, it will copy the filenames of the specified
DropFileSource. These filenames will be used by thread to perform a
drag&drop operation. The calling thread continues uninterupted.
Usage is very simple:
TDragDropThread.Create(DropFileSource1);
Drag&Drop Thread info Q139408:
http://support.microsoft.com/support/kb/articles/Q139/4/08.asp
}
unit DragDropThread;
interface
uses
Classes, DropSource, ActiveX, Windows;
type
TDragDropThread = class(TThread)
private
{ Private declarations }
FFiles : String;
protected
procedure Execute; override;
public
constructor Create(DropFileSource : TDropFileSource);
end;
implementation
{ TDragDropThread }
constructor TDragDropThread.Create(DropFileSource : TDropFileSource);
begin
// Thread will start immediately after creation
inherited Create(False);
// Copy filenames from supplied DropFileSource
FFiles := DropFileSource.Files.Text;
// This thread disappeard when it finishes
FreeOnTerminate := True;
end;
procedure TDragDropThread.Execute;
var
DropFileSource : TDropFileSource;
pt : TPoint;
hwndAttach : HWND;
dwAttachThreadID, dwCurrentThreadID : DWORD;
begin
// Get handle of window under mouse-cursor
GetCursorPos(pt);
hwndAttach := WindowFromPoint(pt);
Assert(hwndAttach 0, 'Unable to find window with drag-object');
// Get thread ID's
dwAttachThreadID := GetWindowThreadProcessId(hwndAttach, nil);
dwCurrentThreadID := GetCurrentThreadId();
// Attach input queues if necessary
if (dwAttachThreadID dwCurrentThreadID) then
AttachThreadInput(dwAttachThreadID, dwCurrentThreadID, True);
// Initialize Ole for this thread
OleInitialize(nil);
try
// create dropsource
DropFileSource := TDropFileSource.Create(nil);
try
DropFileSource.Files.Text := FFiles;
// start drag&drop
DropFileSource.Execute;
finally
// cleanup dropsource
DropFilesource.Free;
end;
finally
// cleanup Ole
OleUninitialize;
end;
// Restore input queues settings
if (dwAttachThreadID dwCurrentThreadID) then
AttachThreadInput(dwAttachThreadID, dwCurrentThreadID, False);
end;
end.