Przenoszenie obrazów podczas przeciągania i upuszczania

Question

Mam obraz na TPanel i inne (puste) TPanels. Chcę przeciągnąć obraz z pierwszego do drugiego panelu za pomocą przeciągania i upuszczania.

Rzeczywiście chcę zobaczyć obraz, gdy przechodzi on z jednego panelu do innego (półprzezroczysty) .

Myślę, że powinienem użyć TDragObject.GetDragImages, ale nie mogę wymyślić, jak skonstruować całą magię.

procedure TForm1.Image1MouseDown(Sender: TObject; Button: TMouseButton; 
    Shift: TShiftState; X, Y: Integer); 
begin 
    Image1.ControlStyle := Image1.ControlStyle + [csDisplayDragImage]; // ??? 
    TImage(Sender).BeginDrag(False); 
end; 

procedure TForm1.Image1StartDrag(Sender: TObject; var DragObject: TDragObject); 
begin 
    // ??? 
end; 

procedure TForm1.Panel1DragOver(Sender, Source: TObject; X, Y: Integer; 
    State: TDragState; var Accept: Boolean); 
begin 
    if (Source is TImage) then 
    Accept := TImage(Source).Parent <> Sender; 
end; 

procedure TForm1.Panel1DragDrop(Sender, Source: TObject; X, Y: Integer); 
begin 
    if (Source is TImage) then 
    begin 
    TImage(Source).Parent := TPanel(Sender); 
    TImage(Source).Align := alClient; 
    end; 
end; 

---

Update - Znalazłem przydatnych artykuł: Implementing Professional Drag & Drop In VCL/CLX Applications

Answer 1

unit Unit3; 

interface 
// 2012 Thomas Wassermann - demo 
uses 
    Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, 
    Dialogs, ExtCtrls; 

type 


    TMyDragObject = class(TDragControlObject) 
    private 
    FImageList:TImageList; 
    FDragSource:TControl; 
    protected 
    function GetDragImages: TDragImageList; override; 
    public 
    Procedure StartDrag(G:TGraphic;p:TPoint;DragSource:TControl); 
    Constructor Create(AControl: TControl); override; 
    Destructor Destroy;override; 
    Property DragSource:TControl read FDragSource; 
    end; 



    TForm3 = class(TForm) 
    Panel1: TPanel; 
    Panel2: TPanel; 
    Image1: TImage; 
    procedure Image1StartDrag(Sender: TObject; var DragObject: TDragObject); 
    procedure FormCreate(Sender: TObject); 
    procedure Panel1DragOver(Sender, Source: TObject; X, Y: Integer; State: TDragState; var Accept: Boolean); 
    procedure FormDestroy(Sender: TObject); 
    procedure Panel1DragDrop(Sender, Source: TObject; X, Y: Integer); 
    private 
    { Private-Deklarationen } 
    FDragObject:TMyDragObject; 
    public 
    { Public-Deklarationen } 
    end; 

var 
    Form3: TForm3; 

implementation 

constructor TMyDragObject.Create(AControl: TControl); 
begin 
    inherited; 
    FImageList:=TImageList.Create(nil); 
end; 

destructor TMyDragObject.Destroy; 
begin 
    FImageList.Free; 
    inherited; 
end; 

function TMyDragObject.GetDragImages: TDragImageList; 
begin 
    Result := FImageList; 
end; 

{$R *.dfm} 

procedure TMyDragObject.StartDrag(G: TGraphic;p:TPoint;DragSource:TControl); 
var 
bmp:TBitMap; 
begin 
    FDragSource := DragSource; 
    bmp:=TBitMap.Create; 
    try 
    FImageList.Width := g.Width; 
    FImageList.Height := g.Height; 
    bmp.Width := g.Width; 
    bmp.Height := g.Height; 
    bmp.Canvas.Draw(0,0,g); 
    FImageList.Add(bmp,nil); 
    finally 
    bmp.Free; 
    end; 
    FImageList.SetDragImage(0,p.x,p.y) 
end; 

procedure TForm3.FormCreate(Sender: TObject); 
var 
i:Integer; 
begin 
    ControlStyle := ControlStyle + [csDisplayDragImage]; 
    for I := 0 to ControlCount -1 do 
     if Controls[i] is TPanel then 
     TPanel(Controls[i]).ControlStyle := TPanel(Controls[i]).ControlStyle + [csDisplayDragImage]; 
    ReportMemoryLeaksOnShutDown := True; 
end; 

procedure TForm3.FormDestroy(Sender: TObject); 
begin 
    if Assigned(FDragObject) then FDragObject.Free; 
end; 

procedure TForm3.Image1StartDrag(Sender: TObject; var DragObject: TDragObject); 
var 
p:TPoint; 

begin 
    p:=TImage(Sender).ScreenToClient(mouse.cursorpos); 
    if Assigned(FDragObject) then FDragObject.Free; 
    FDragObject := TMyDragObject.Create(TImage(Sender)); 
    FDragObject.StartDrag(TImage(Sender).Picture.Graphic,p,TImage(Sender)); 
    DragObject := FDragObject; 
end; 

procedure TForm3.Panel1DragDrop(Sender, Source: TObject; X, Y: Integer); 
begin 
    if FDragObject.DragSource is TImage then 
    TImage(FDragObject.DragSource).Parent := TPanel(Sender); 
end; 

procedure TForm3.Panel1DragOver(Sender, Source: TObject; X, Y: Integer; State: TDragState; var Accept: Boolean); 
begin 
    Accept := Source is TMyDragObject; 
end; 

end.