Demo pour Reinhard

Ma super demo

Drag And Drop from Windows Explorer

This article presents the required code to handle drag& drop of images from Windows Explorer to your Delphi application. The demo code shows how to drop images on a TListView and to drag & drop from TListView to a TImage.

The code is fairly basic and made so that it can be clearly understood and applied to other types of controls.

Drag & Drop from windows Explorer is handled by an application by registering a window handle along with an instance of an IDropTarget interface.

To make to code easy to reuse, I encapsulated the IDropTarget implementation into a class named TDropTarget and expose the features the Delphi way: using event.

To allow Drag & Drop from Windows Explorer to one of your form, you have to create an instance of TDropTarget and call his Register method passing the form’s handle. Of course you have to assign the events to handler in your form. The events handle all drag and drop operation:

DropAllowed event is called once when the dragged files are entering the area of the registered window. The event handler must set the “Allowed” var argument to TRUE if dropping the file(s) is allowed at the given point.

DragOver event is called as mouse move above the registered window. The event handler must set the “Allowed” var argument to TRUE if dropping the file(s) is allowed at the given point.

Drop event is called when the user drops the files.

DragLeave event is called when the dragged files leave the registered window area.

I could have made a component of TDropTarget but I didn’t. It is a simple object deriving from Object. As it implements an interface IDroptarget, beside the methods of this interface, the object also has to handle _AddRef, _Release and QueryInterface methods which exist in all interfaces. Here we use TObject life cycle, so those methods are simply do-nothing methods.

The code required in your form include creating the object in the form’s contructor (or FormCreate event), assign the event handlers and call register. And of course free the object instance in the destructor:

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constructor TDragDropMainForm.Create(AOwner: TComponent); begin     inherited Create(AOwner);     FDropTarget               := TDropTarget.Create;     FDropTarget.OnDropAllowed := ImageDropAllowedHandler;     FDropTarget.OnDrop        := ImageDropHandler;     FDropTarget.OnDragOver    := ImageDragOverHandler;     FDropTarget.Register(Handle); end;   destructor TDragDropMainForm.Destroy; begin     FreeandNil(FDropTarget);     inherited; end;

The demo application uses a TListView in vsList view mode and a TImage. The ListView accept the dropped images from Windows Explorer while TImage accepte images dropped from TListView. It is a good exercise for you to make TImage accept image also from Windows Explorer.

The demo application doesn’t show image in real size in TListView. Rather, it creates a thumbnail which is displayed in the list view. The thumbnails are stored on disk in the same folder as the original image and are only created if it doesn’t exist yet, or if the original image has been modified. Storing the thumbnail on disk could be a problem in some application because it requires write permission. In my application (Well the application I extracted this code from), it is an advantage because the images are very large and it takes time to create the thumbnails. Keeping the thumbnails on disk improve performance.

Thumbnails are created using GDI+ (See my other blog article about it: http://francois-piette.blogspot.be/2013/05/opensource-gdi-library.html). The code is really easy:

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Image := TGPImage.Create(AFileName);    Thumbnail := Image.GetThumbnailImage(ThWidth, ThHeight, nil, nil);    Quality := 50;    Params := TGPEncoderParameters.Create;    Params.Add(EncoderQuality, Quality);    Thumbnail.Save(AThumbFileName, TGPImageFormat.Jpeg, Params);

A last note about the demo application: I used custom draw of the ListView items so that it looks exactly how I require it. All list view items are represented by a class named TImageListViewItem. I have selected this representation because in the real application this demo is extracted from, there is a lot of information about each image. The class is really handy to hold the information and the processing related to it.


Here after is the complete source code. There are mainly two files: DropHanlder.pas and DragDropMain.pas. You can also download a zip file with the complete project. See my website at: http://www.overbyte.be/frame_index.html?redirTo=/blog_source_code.html

DropHandler.pas

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unit DropHandler;   interface   uses     Windows, Types, Classes, SysUtils, ShellAPI, ActiveX;   type     TStringArray      = array of String;       TDropAllowedEvent = procedure (Sender            : TObject;                                    const FileNames   : array of String;                                    const grfKeyState : Longint;                                    const pt          : TPoint;                                    var   Allowed     : Boolean)                                  of object;     TDragOverEvent    = procedure (Sender            : TObject;                                    const grfKeyState : Longint;                                    const pt          : TPoint;                                    var   Allowed     : Boolean)                                  of object;     TDropEvent        =  procedure (Sender           : TObject;                                     const DropPoint  : TPoint;                                     const FileNames  : array of String)                                  of object;       TDropTarget = class(TObject, IDropTarget)     private         FRegisteredHandle : HWND;         FDropAllowed      : Boolean;         FOnDropAllowed    : TDropAllowedEvent;         FOnDrop           : TDropEvent;         FOnDragOver       : TDragOverEvent;         FOnDragLeave      : TNotifyEvent;         procedure GetFileNames(const dataObj : IDataObject;                                var FileNames : TStringArray);         function  DragEnter(const dataObj : IDataObject;                             grfKeyState   : Integer;                             pt            : TPoint;                             var dwEffect  : Integer): HResult; stdcall;         function  DragOver(grfKeyState  : Longint;                            pt           : TPoint;                            var dwEffect : Longint): HResult; stdcall;         function  DragLeave: HResult; stdcall;         function  Drop(const dataObj : IDataObject;                        grfKeyState   : Longint;                        pt            : TPoint;                        var dwEffect  : Longint): HResult; stdcall;         function _AddRef: Integer; stdcall;         function _Release: Integer;  stdcall;         function QueryInterface(const IID: TGUID; out Obj): HResult;  stdcall;     public         destructor  Destroy; override;         // Call Register() with a window handle so that that window starts         // accepting dropped files. Events will then be generated.         function    Register(AHandle : HWnd) : HResult;         // Stop accepting files dropped on the registered window.         procedure   Revoke;         // DropAllowed event is called once when the dragged files are         // entering the area of the registered window.         // The event handler must set the Allowed var argument to TRUE if         // dropping the file(s) is allowed at the given point         property OnDropAllowed : TDropAllowedEvent read  FOnDropAllowed                                                    write FOnDropAllowed;         // DragOver event is called as mouse move above the registered window         // The event handler must set the Allowed var argument to TRUE if         // dropping the file(s) is allowed at the given point         property OnDragOver    : TDragOverEvent    read  FOnDragOver                                                    write FOnDragOver;         // Drop event is called when the user drops the files.         property OnDrop        : TDropEvent        read  FOnDrop                                                    write FOnDrop;         // DragLeave event is called when the dragged files leave the         // registered window area.         property OnDragLeave   : TNotifyEvent      read  FOnDragLeave                                                    write FOnDragLeave;     end;   implementation     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} function TDropTarget.Register(AHandle: HWnd): HResult; begin     if FRegisteredHandle = AHandle then begin         Result := S_OK;         Exit;     end;     if FRegisteredHandle <> 0 then         Revoke;     FRegisteredHandle := AHandle;     Result  := ActiveX.RegisterDragDrop(FRegisteredHandle, Self); end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} procedure TDropTarget.Revoke; begin     if FRegisteredHandle <> 0 then begin         ActiveX.RevokeDragDrop(FRegisteredHandle);         FRegisteredHandle := 0;     end; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} destructor TDropTarget.Destroy; begin     Revoke;     inherited Destroy; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} procedure TDropTarget.GetFileNames(     const dataObj : IDataObject;     var FileNames : TStringArray); var     I           : Integer;     FormatetcIn : TFormatEtc;     Medium      : TStgMedium;     DropHandle  : HDROP; begin     FileNames            := nil;     FormatetcIn.cfFormat := CF_HDROP;     FormatetcIn.ptd      := nil;     FormatetcIn.dwAspect := DVASPECT_CONTENT;     FormatetcIn.lindex   := -1;     FormatetcIn.tymed    := TYMED_HGLOBAL;     if dataObj.GetData(FormatetcIn, Medium) = S_OK then begin         DropHandle := HDROP(Medium.hGlobal);         SetLength(FileNames, DragQueryFile(DropHandle, $FFFFFFFF, nil, 0));         for I := 0 to high(FileNames) do begin             SetLength(FileNames[I], DragQueryFile(DropHandle, I, nil, 0));             DragQueryFile(DropHandle, I, @FileNames[I][1],                           Length(FileNames[I]) + 1);         end;     end; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} function TDropTarget.DragEnter(     const dataObj : IDataObject;     grfKeyState   : Integer;     pt            : TPoint;     var dwEffect  : Integer): HResult; var     FileNames: TStringArray; begin     Result := S_OK;     try         GetFileNames(dataObj, FileNames);         if (Length(FileNames) > 0) and Assigned(FOnDropAllowed) then begin             FDropAllowed := FALSE;             FOnDropAllowed(Self, FileNames, grfKeyState, pt, FDropAllowed);         end;         if FDropAllowed then             dwEffect := DROPEFFECT_COPY         else             dwEffect := DROPEFFECT_NONE;     except         Result := E_UNEXPECTED;     end; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} function TDropTarget.DragLeave: HResult; begin     if Assigned(FOnDragLeave) then         FOnDragLeave(Self);     Result := S_OK; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} function TDropTarget.DragOver(     grfKeyState  : Integer;     pt           : TPoint;     var dwEffect : Integer): HResult; begin     Result := S_OK;     try         if Assigned(FOnDragOver) then             FOnDragOver(Self, grfKeyState, pt, FDropAllowed);         if FDropAllowed then             dwEffect := DROPEFFECT_COPY         else             dwEffect := DROPEFFECT_NONE;     except         Result := E_UNEXPECTED;     end; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} function TDropTarget.Drop(     const dataObj : IDataObject;     grfKeyState   : Integer;     pt            : TPoint;     var dwEffect  : Integer): HResult; var     FileNames: TStringArray; begin     Result := S_OK;     try         GetFileNames(dataObj, FileNames);         if (Length(FileNames) > 0) and Assigned(FOnDrop) then             FOnDrop(Self, Pt, FileNames);     except         // Silently ignore any exception bacsue if required, they should         // be handled in OnDrop event handler.     end; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} function TDropTarget.QueryInterface(const IID: TGUID; out Obj): HResult; begin     if GetInterface(IID, Obj) then         Result := 0     else         Result := E_NOINTERFACE; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} function TDropTarget._AddRef: Integer; begin     // We don't use reference counting in this object     // We need _AddRef because RegisterDragDrop API call it     Result := 1; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} function TDropTarget._Release: Integer; begin     // We don't use reference counting in this object     // We need _Release because RevokeDragDrop API call it     Result := 1; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *}   end.

DragDropMain.pas

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unit DragDropMain;   interface   uses     Windows, Messages, Types, SysUtils, Variants, Classes, Graphics,     StdCtrls, ExtCtrls, Controls, ComCtrls, CommCtrl, Forms, Dialogs,     Jpeg, ImgList,     GdiPlus,     DropHandler;   const     AtEndOfPipe      = -1;     AtTopOfPipe      = -2;     THUMBNAIL_SIZE   = 64;     THUMBNAIL_MARGIN = 8;     // List of accepted image file extensions     Exts     : array [0..3] of String = ('.jpg', '.png', '.bmp', '.tif');   type     TImageListViewItem = class     public         FileName          : String;         Bitmap            : TBitmap;         Data              : TObject;         ThumbnailFileName : String;         constructor Create(const AFileName          : String;                            const AThumbnailFileName : String;                            const AItem              : TListItem;                            const AWidth             : Integer;                            const AHeight            : Integer);         destructor  Destroy; override;     end;       TDragDropMainForm = class(TForm)         ListView1: TListView;         Splitter1: TSplitter;         Image1: TImage;         procedure ListView1CustomDrawItem(Sender          : TCustomListView;                                           Item            : TListItem;                                           State           : TCustomDrawState;                                           var DefaultDraw : Boolean);         procedure ListView1Deletion(Sender : TObject;                                     Item   : TListItem);         procedure ListView1MouseDown(Sender : TObject;                                      Button : TMouseButton;                                      Shift  : TShiftState;                                      X, Y   : Integer);         procedure ListView1MouseMove(Sender: TObject;                                      Shift : TShiftState;                                      X, Y  : Integer);         procedure ListView1MouseUp(Sender : TObject;                                    Button : TMouseButton;                                    Shift  : TShiftState;                                    X, Y   : Integer);     private         FDropTarget              : TDropTarget;         FMouseDownPt             : TPoint;         FMouseMovePt             : TPoint;         FMouseDownFlag           : Boolean;         FDraggingImage           : Boolean;         procedure ImageDragOverHandler(Sender            : TObject;                                        const grfKeyState : Longint;                                        const pt          : TPoint;                                        var   Allowed     : Boolean);         procedure ImageDropAllowedHandler(Sender            : TObject;                                           const FileNames   : array of string;                                           const GrfKeyState : Integer;                                           const Pt          : TPoint;                                           var   Allowed     : Boolean);         procedure ImageDropHandler(Sender          : TObject;                                    const DropPoint : TPoint;                                    const FileNames : array of string);         function  DropImage(const AFileName : String;                             XScreen         : Integer;                             YScreen         : Integer): Boolean;         procedure CreateThumbnail(const AFileName      : String;                                      var   AThumbFileName : String);         function  KnownExtension(const FileName : String): Boolean; overload;         function  KnownExtension(const FileNames: array of string): Boolean; overload;     public         constructor Create(AOwner : TComponent); override;         destructor  Destroy; override;         procedure AddImage(const FileName : String;                            BeforeIndex    : Integer);         procedure MoveImage(IFrom, ITo: Integer);         procedure RemoveImage(Index: Integer); overload;         function  FindImage(const FileName: String): Integer;         function  AppendImage(const FileName: String): Integer;     end;   function ReplaceThumb(const FileName : String) : String; function ListViewMouseToItem(     Pt           : TPoint;     LV           : TListView;     var ColIndex : Integer): TListItem;   var   DragDropMainForm: TDragDropMainForm;   implementation   {$R *.dfm}   {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *}   { TDragDropMainForm }   {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} constructor TDragDropMainForm.Create(AOwner: TComponent); begin     inherited Create(AOwner);     FDropTarget               := TDropTarget.Create;     FDropTarget.OnDropAllowed := ImageDropAllowedHandler;     FDropTarget.OnDrop        := ImageDropHandler;     FDropTarget.OnDragOver    := ImageDragOverHandler;     FDropTarget.Register(Handle);       // To have TListView work correctly in vsList view mode, we must have     // at least one group, one column and a SmallImages image list.     ListView1.Groups.Clear;     ListView1.Groups.Add;     ListView1.Columns.Clear;     ListView1.Columns.Add;     // Height of displayed image is set by height of SmallImages     ListView1.SmallImages        := TImageList.Create(Self);     ListView1.SmallImages.Height := THUMBNAIL_SIZE + 2 * THUMBNAIL_MARGIN;     // Width of displayed image is set by ListView_SetColumnWidth macro with     // column index set to zero.     ListView_SetColumnWidth(ListView1.Handle, 0, THUMBNAIL_SIZE + 2 * THUMBNAIL_MARGIN); end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} destructor TDragDropMainForm.Destroy; begin     FreeandNil(FDropTarget);     inherited; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} procedure TDragDropMainForm.ImageDragOverHandler(     Sender            : TObject;     const grfKeyState : Longint;     const pt          : TPoint;     var   Allowed     : Boolean); begin     Allowed := TRUE;     if not PtInRect(ListView1.BoundsRect, ListView1.ScreenToClient(Pt)) then begin         Allowed := FALSE;         Exit;     end; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} procedure TDragDropMainForm.ImageDropAllowedHandler(     Sender            : TObject;     const FileNames   : array of string;     const GrfKeyState : Integer;     const Pt          : TPoint;     var   Allowed     : Boolean); begin     Allowed := KnownExtension(FileNames); end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} procedure TDragDropMainForm.ImageDropHandler(     Sender          : TObject;     const DropPoint : TPoint;     const FileNames : array of string); var     I : Integer; begin     for I := 0 to High(FileNames) do         DropImage(ReplaceThumb(FileNames[I]), DropPoint.X, DropPoint.Y); end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} function TDragDropMainForm.DropImage(     const AFileName : String;     XScreen         : Integer;     YScreen         : Integer) : Boolean; var     Pt       : TPoint;     Item     : TListItem;     ColIndex : Integer; begin     Result := FALSE;     // First check if the extension is allowed     if not KnownExtension(AFileName) then begin         ShowMessage('Unacceptable file type (' +                     ExtractFileExt(AFileName) + ')');         Exit;     end;       // Check if we already got the image     if FindImage(AFileName) >= 0 then begin         ShowMessage(AFileName + #10 + 'Already in the ListView, ignoring');         Exit;     end;       // Check if the drop point is inside the ListView     Pt := ListView1.ScreenToClient(Point(XScreen, YScreen));     if not PtInRect(ListView1.BoundsRect, Pt) then         Exit;     // Check if dropped on an existing item     Item := ListViewMouseToItem(Pt, ListView1, ColIndex);     if not Assigned(Item) then         AppendImage(AFileName)           // Not on an item, add at the end     else         AddImage(AFileName, Item.Index); // Insert before the item     Result   := TRUE; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} procedure TDragDropMainForm.ListView1CustomDrawItem(     Sender          : TCustomListView;     Item            : TListItem;     State           : TCustomDrawState;     var DefaultDraw : Boolean); var     Bitmap  : TBitMap;     Rc1     : TRect;     Rc2     : TRect;     Rc3     : TRect;     ACanvas : TCanvas;     YOff    : Integer;     XOff    : Integer; begin     ACanvas := Sender.Canvas;     Rc1 := Item.DisplayRect(drBounds);     if Assigned(Item.Data) then begin         Bitmap := TImageListViewItem(Item.Data).Bitmap;         // Center the bitmap         YOff := ((THUMBNAIL_SIZE - BitMap.Height) div 2) + THUMBNAIL_MARGIN;         XOff := ((THUMBNAIL_SIZE - Bitmap.Width) div 2) + THUMBNAIL_MARGIN;         ACanvas.Draw(Rc1.Left + 2 + XOff, Rc1.Top + 2 + YOff, Bitmap);           // Draw a double FrameRect around the image with a color depending         // on the status of the image         Rc2.Left   := Rc1.Left + XOff;         Rc2.Top    := Rc1.Top  + YOff;         Rc2.Right  := Rc1.Left + Bitmap.Width  + 4 + XOff;         Rc2.Bottom := Rc1.Top  + Bitmap.Height + 4 + YOff;         Rc3.Left   := Rc1.Left + 1 + XOff;         Rc3.Top    := Rc1.Top  + 1 + YOff;         Rc3.Right  := Rc1.Left + Bitmap.Width  + 3 + XOff;         Rc3.Bottom := Rc1.Top  + Bitmap.Height + 3 + YOff;           if cdsSelected in State then             ACanvas.Brush.Color := clBlue         else if cdsHot in State then             ACanvas.Brush.Color := clRed         else             ACanvas.Brush.Color := ListView1.Color;           ACanvas.FrameRect(Rc2);         ACanvas.FrameRect(Rc3);           DefaultDraw := FALSE;     end; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} procedure TDragDropMainForm.ListView1Deletion(     Sender : TObject;     Item   : TListItem); begin     if Assigned(Item.Data) then         TObject(Item.Data).Free; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} procedure TDragDropMainForm.ListView1MouseDown(     Sender : TObject;     Button : TMouseButton;     Shift  : TShiftState;     X, Y   : Integer); begin     if ssLeft in Shift then begin         FMouseDownPt := Point(X, Y);         FMouseDownFlag := TRUE;     end; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} procedure TDragDropMainForm.ListView1MouseMove(     Sender : TObject;     Shift  : TShiftState;     X, Y   : Integer); var     Item     : TListItem;     ColIndex : Integer; begin     FMouseMovePt := Point(X, Y);     if not FMouseDownFlag then         Exit;     if not FDraggingImage then begin         Item := ListViewMouseToItem(FMouseDownPt, ListView1, ColIndex);         if Assigned(Item) then begin             FDraggingImage := TRUE;             Screen.Cursor  := crDrag;             SetCaptureControl(ListView1);         end;     end; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} procedure TDragDropMainForm.ListView1MouseUp(     Sender : TObject;     Button : TMouseButton;     Shift  : TShiftState;     X, Y   : Integer); var     Pt       : TPoint;     ItemFrom : TListItem;     ItemTo   : TListItem;     ColIndex : Integer;     LV       : TListView;     IFrom    : Integer;     ITo      : Integer;     FileName : String; begin     FMouseDownFlag := FALSE;     if FDraggingImage then begin         FDraggingImage := FALSE;         Screen.Cursor  := crDefault;         SetCaptureControl(nil);         LV       := Sender as TListView;         ItemFrom := ListViewMouseToItem(FMouseDownPt, LV, ColIndex);         ItemTo   := ListViewMouseToItem(Point(X, Y),  LV, ColIndex);         IFrom    := ItemFrom.Index;         FileName := TImageListViewItem(ItemFrom.Data).FileName;         if not FileExists(FileName) then begin             if Application.MessageBox(                    PChar('File "' + FileName + '" doesn''t exist anymore' +                          #10 + 'Remove from ListView ?'), 'WARNING',                          MB_YESNO + MB_DEFBUTTON2) = IDYES then begin                 RemoveImage(IFrom);                 Exit;             end;         end;           if Assigned(ItemTo) then begin             // Drop inside of the pipe, move items around             if ItemTo <> ItemFrom then begin                 ITo   := ItemTo.Index;                 MoveImage(IFrom, ITo);             end;         end         else begin             if PtInRect(LV.BoundsRect, Point(X, Y)) then begin                 // Drop on the listview but not on an item, just move at the end                 ITo := LV.Items.Count - 1;                 MoveImage(IFrom, ITo);             end             else begin                 // Drop outside of the ListView                 // Check if within Image1                 Pt := ListView1.ClientToScreen(Point(X, Y));                 Pt := Image1.ScreenToClient(Pt);                 if (Pt.X >= 0) and (Pt.X < Image1.Width) and                    (Pt.Y >= 0) and (Pt.Y < Image1.Height) then begin                     Image1.Picture.LoadFromFile(TImageListViewItem(ItemFrom.Data).FileName);                 end;             end;         end;     end; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} procedure TDragDropMainForm.AddImage(     const FileName : String;     BeforeIndex    : Integer);  // Index of the item where to insert (before) var     IFrom : Integer; begin     IFrom := AppendImage(FileName);     if IFrom < 0 then         Exit;            // Not found or already exist, not added     if BeforeIndex = AtTopOfPipe then         MoveImage(IFrom, 0)     else if (BeforeIndex >= 0) and (BeforeIndex < ListView1.Items.Count) then         MoveImage(IFrom, BeforeIndex); end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} // Search if a give file already exists in list. // Return -1 if not found // Return item index if already in the list function TDragDropMainForm.FindImage(const FileName: String): Integer; begin     for Result := 0 to ListView1.Items.Count - 1 do begin         if SameText(FileName,                     TImageListViewItem(ListView1.Items[Result].Data).FileName) then             Exit;     end;     Result := -1; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} procedure TDragDropMainForm.MoveImage(     IFrom : Integer;     ITo   : Integer); var     Data     : Pointer;     Capt     : String;     I        : Integer; begin     if IFrom < ITo then begin         Data := ListView1.Items[IFrom].Data;         Capt := ListView1.Items[IFrom].Caption;         for I := IFrom to ITo - 1 do begin             ListView1.Items[I].Data    := ListView1.Items[I + 1].Data;             ListView1.Items[I].Caption := ListView1.Items[I + 1].Caption;             TImageListViewItem(ListView1.Items[I].Data).Data := ListView1.Items[I];         end;         ListView1.Items[ITo].Data    := Data;         ListView1.Items[ITo].Caption := Capt;         TImageListViewItem(ListView1.Items[ITo].Data).Data := ListView1.Items[ITo];     end     else begin         Data := ListView1.Items[IFrom].Data;         Capt := ListView1.Items[IFrom].Caption;         for I := IFrom downto ITo + 1 do begin             ListView1.Items[I].Data    := ListView1.Items[I - 1].Data;             ListView1.Items[I].Caption := ListView1.Items[I - 1].Caption;             TImageListViewItem(ListView1.Items[I].Data).Data := ListView1.Items[I];         end;         ListView1.Items[ITo].Data    := Data;         ListView1.Items[ITo].Caption := Caption;         TImageListViewItem(ListView1.Items[ITo].Data).Data := ListView1.Items[ITo];     end;     Windows.InvalidateRect(ListView1.Handle, nil, FALSE); end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} function TDragDropMainForm.KnownExtension(     const FileName : String) : Boolean; var     Ext : String;     I   : Integer; begin     Result := FALSE;     Ext := ExtractFileExt(FileName);     for I := Low(Exts) to High(Exts) do begin         if SameText(Ext, Exts[I]) then begin             Result := TRUE;             Exit;         end;     end; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} function TDragDropMainForm.KnownExtension(     const FileNames : array of string) : Boolean; var     I : Integer; begin     Result := FALSE;     for I := Low(FileNames) to High(FileNames) do begin         if KnownExtension(FileNames[I]) then begin             Result := TRUE;             Exit;         end;     end; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} // Given a filename which could be a thumbnail filename, return either the // filename unchanged or the image which is represented by thumbnail function ReplaceThumb(const FileName : String) : String; const     ThSuffix = '.thumb.jpg'; var     S : String;     I : Integer; begin     if not SameText(Copy(FileName, Length(FileName) - Length(ThSuffix) + 1, 200),                     ThSuffix) then begin         Result := FileName;         Exit;     end;       S := Copy(FileName, 1, Length(FileName) - Length(ThSuffix));     for I := Low(Exts) to High(Exts) do begin         Result := S + Exts[I];         if FileExists(Result) then             Exit;     end;     Result := FileName; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} // ColIndex returns the column index, not the SubItem index. function ListViewMouseToItem(     Pt           : TPoint;     LV           : TListView;     var ColIndex : Integer): TListItem; var     Info : TLVHitTestInfo; begin //    Pt := LV.ScreenToClient(Mouse.Cursorpos);     Result := LV.GetItemAt(Pt.X, Pt.Y);     if Assigned(Result) then         ColIndex := 0     else begin         FillChar(Info, SizeOf(Info), 0);         Info.Pt := Pt;         if LV.Perform(LVM_SUBITEMHITTEST, 0, LParam(@Info)) <> -1 then begin             Result   := LV.Items[Info.iItem];             ColIndex := Info.iSubItem;         end;     end; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} function TDragDropMainForm.AppendImage(     const FileName : String) : Integer; var     Item              : TListItem;     ThumbnailFileName : String; begin     Result := -1;     if not FileExists(FileName) then         Exit;     if FindImage(FileName) >= 0 then         Exit;   // Already exist, do not add     ThumbnailFileName := '';     CreateThumbnail(FileName, ThumbnailFileName);     Item         := ListView1.Items.Add;     // Item.Caption is used as the hint     Item.Caption := FileName;     Item.Data    := TImageListViewItem.Create(FileName,                                           ThumbnailFileName,                                           Item,                                           THUMBNAIL_SIZE,                                           THUMBNAIL_SIZE);     Result := Item.Index; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} procedure TDragDropMainForm.RemoveImage(Index : Integer); var     I : Integer; begin     ListView1.Items.Delete(Index);     for I := Index to ListView1.Items.Count - 1 do         TImageListViewItem(ListView1.Items[I].Data).Data := ListView1.Items[I];     Windows.InvalidateRect(ListView1.Handle, nil, FALSE); end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} procedure TDragDropMainForm.CreateThumbnail(     const AFileName      : String;     var   AThumbFileName : String); var     ThWidth          : Integer;     ThHeight         : Integer;     FTFile           : TDateTime;     FTThumb          : TDateTime;     Image            : IGPImage;     Thumbnail        : IGPImage;     Params           : IGPEncoderParameters;     Quality          : Int32; begin     AThumbFileName := ChangeFileExt(AFileName, '.thumb.jpg');     if FileExists(AThumbFileName) then begin         // Thumbnail file must be dated AFTER original file so that it         // is recreated when the original file is changed.         FileAge(AFileName, FTFile);         FileAge(AThumbFileName, FTThumb);         if FTThumb >= FTFile then             Exit;     end;       Image := TGPImage.Create(AFileName);       // Thumbnail preserve original width/height ratio     if Image.Width > Image.Height then begin         ThWidth  := THUMBNAIL_SIZE;         ThHeight := THUMBNAIL_SIZE * Image.Height div Image.Width;     end     else if Image.Width < Image.Height then begin         ThHeight := THUMBNAIL_SIZE;         ThWidth  := THUMBNAIL_SIZE * Image.Width div Image.Height;     end     else begin         ThWidth  := THUMBNAIL_SIZE;         ThHeight := THUMBNAIL_SIZE;     end;       Thumbnail := Image.GetThumbnailImage(ThWidth, ThHeight, nil, nil);     Quality := 50;     Params := TGPEncoderParameters.Create;     Params.Add(EncoderQuality, Quality);     Thumbnail.Save(AThumbFileName, TGPImageFormat.Jpeg, Params); end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *}   { TImagePipeItem }   {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} constructor TImageListViewItem.Create(     const AFileName          : String;     const AThumbnailFileName : String;     const AItem              : TListItem;     const AWidth             : Integer;     const AHeight            : Integer); var     JpegImg : TJPEGImage;     Ext     : String; begin     inherited Create;     Data               := AItem;     FileName           := AFileName;     ThumbnailFileName  := AThumbnailFileName;     Bitmap             := TBitMap.Create;     if (AThumbnailFileName <> '') and (FileExists(AThumbnailFileName)) then begin         Ext := ExtractFileExt(AThumbnailFileName);         if SameText(Ext, '.jpg') then begin             JpegImg := TJPEGImage.Create;             try                 JpegImg.LoadFromFile(AThumbnailFileName);                 BitMap.Width  := JpegImg.Width;                 BitMap.Height := JpegImg.Height;                 BitMap.Canvas.Draw(0, 0, JpegImg);             finally                 JpegImg.Destroy;             end;         end         else if SameText(Ext, '.bmp') then             Bitmap.LoadFromFile(AThumbnailFileName)     end     else begin         Bitmap.Width       := AWidth - 4;         Bitmap.Height      := AHeight - 4;         Bitmap.PixelFormat := pf24bit;         Bitmap.Canvas.MoveTo(0, 0);         BitMap.Canvas.LineTo(Bitmap.Width, Bitmap.Height);         Bitmap.Canvas.MoveTo(Bitmap.Width, 0);         BitMap.Canvas.LineTo(0, Bitmap.Height);         BitMap.Canvas.LineTo(0, 0);         BitMap.Canvas.LineTo(Bitmap.Width - 1, 0);         BitMap.Canvas.LineTo(Bitmap.Width - 1, Bitmap.Height - 1);         BitMap.Canvas.LineTo(0, Bitmap.Height - 1);         Bitmap.Canvas.TextOut(4, 4, AFileName);     end; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *} destructor TImageListViewItem.Destroy; begin     FreeAndNil(Bitmap);     inherited Destroy; end;     {* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *}   end.

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Test Number 2

Author:       François PIETTE @ OverByte
Creation:     Feb 16, 2013
Description:  TCommQueue is a generic class aimed at handling "buffers" in
              an efficient way so that it can be used in high speed systems.
              The idea is to have the minimum number of memory allocation.
              To manage the buffers, the class uses 3 linked lists: Active,
              inactive and acquired buffers.
              When adding a buffer to the queue, the Add method first look at
              the inactive queue to get an inactive buffer and reuse it. If
              no inactive buffer is available, then a new one is allocated.
              When a buffer is not more needed, the remove method actually move
              the buffer to the inactive buffer list.
              The queue offers methods to iterate thru it: first, next, previous
              and last. Each method return a pointer to the buffer.
              The class is multithread safe: it make use of a critical section
              to protect his internal data structures.
              To be completely thread safe according to the producer/consumer
              pattern, there are a pair of additional methods: AcquireItem and
              ReleaseItem. AcquireItem will get a pointer to the oldest buffer
              in the queue and move it to the acquired buffer list. Only a
              single thread is able to get a pointer to a given buffer.
              Once a thread has finished processing the buffer, it must call
              the ReleaseItem method passing the pointer so that the buffer is
              moved to the inactive list for later reuse.
              A last method, FreeAllInactiveItems, can be use to free all
              inactive buffer. This should probably never used unless the
              application is short of memory. Freeing all inactive buffer
              obviously frre memory, but has an impact on performance: new
              buffer must be allocated.
              On my system, allocating one million of buffers having 0.5 kB each
              takes 265 mS the first time. It takes 109 mS to remove all.
              Then it only takes 145 mS to get another one million buffers.
              It goes faster the second (and subsequent times) because no
              memory allocation take place. Only pointers in the linked lists
              are updated.
              Note about multithreading support: All operations on the linked
              lists are protected by a critical section so each list will
              remain coherent even if different threads use the same queue at
              the same time. However, if several thread have to process items
              in the queue (consumers), they MUST use AcquireItem and
              ReleaseItem exclusively. Other methods are for a single consumer
              thread. In all cases, multiple thread can be producers, that is
              add items in the queue.
Version:      1.00
History:

Test number 1

This is a test.

?

1 2 3 4 5 6

function TMyObjct.HelloSyntaxHighlighter(const S : String); begin     WriteLn(S);     if S < '' then         WriteLn('Test'); end;

Please ignore.