我正在StartDrag上创建自定义DragObject的实例:
procedure TForm1.GridStartDrag(Sender: TObject;
var DragObject: TDragObject);
begin
DragObject := TMyDragControlObject.Create(Sender as TcxGridSite);
end;
最近在DragOver上的另一个网格上:
procedure TForm1.SecondGridDragOver(Sender, Source: TObject; X,
Y: Integer; State: TDragState; var Accept: Boolean);
begin
Accept := False;
if Source is TMyDragControlObject then
with TMyDragControlObject(Source) do
// using TcxGrid
if (Control is TcxGridSite) or (Control is TcxGrid) then begin
Accept := True
// checking the record value on grid
// the label of drag cursor will be different
// getting the record value works fine!
if RecordOnGrid.Value > 5 then
DragOverPaint(FImageList, 'You can drop here!');
else begin
Accept := false;
DragOverPaint(FImageList, 'You can''t drop here!');
end
end;
end;
我的DragOverPaint程序:
procedure TForm1.DragOverPaint(ImageList: TImageList; AValue: string);
var ABmp: TBitmap;
begin
if not Assigned(ImageList) then Exit;
ABmp := TBitmap.Create();
try
with ABmp.Canvas do begin
ABmp.Width := TextWidth(AValue);
ABmp.Height := TextHeight(AValue);
TextOut(0, 0, AValue);
end;
ImageList.BeginUpdate;
ImageList.Clear;
ImageList.Width := ABmp.Width;
ImageList.Height := ABmp.Height;
ImageList.AddMasked(ABmp, clNone);
ImageList.EndUpdate;
finally
ABmp.Free();
end;
Repaint;
end;
我希望它根据网格记录值重新绘制DragImageList,但图像列表在已经绘制时不会刷新。
答案 0 :(得分:6)
ImageList开始拖动后,您无法通过更改ImageList来更改拖动图像,因为Windows会创建另一个专门用于拖动的临时混合ImageList。因此,您必须再次结束,更改并启动ImageList拖动(这不等于结束并启动完整的VCL拖动操作,只是WinAPI ImageList)。结果/缺点是图像转换时略微颤动。
更改图像的时刻是“已接受”更改(在此特定情况下)。可以在OnDragOver中处理这个问题,但既然你已经创建了一个自己的DragObject,你也可以覆盖它为TDragObject设计的方法:
type
TControlAccess = class(TControl);
TMyDragControlObject = class(TDragControlObjectEx)
private
FDragImages: TDragImageList;
FPrevAccepted: Boolean;
protected
function GetDragCursor(Accepted: Boolean; X, Y: Integer): TCursor; override;
function GetDragImages: TDragImageList; override;
public
destructor Destroy; override;
end;
{ TMyDragControlObject }
destructor TMyDragControlObject.Destroy;
begin
FDragImages.Free;
inherited Destroy;
end;
function TMyDragControlObject.GetDragCursor(Accepted: Boolean; X,
Y: Integer): TCursor;
begin
if FPrevAccepted <> Accepted then
with FDragImages do
begin
EndDrag;
SetDragImage(Ord(Accepted), 0, 0);
BeginDrag(GetDesktopWindow, X, Y);
end;
FPrevAccepted := Accepted;
Result := inherited GetDragCursor(Accepted, X, Y);
end;
function TMyDragControlObject.GetDragImages: TDragImageList;
const
SNoDrop = 'You can''t drop here!!';
SDrop = 'You can drop here.';
Margin = 20;
var
Bmp: TBitmap;
begin
if FDragImages = nil then
begin
FDragImages := TDragImageList.Create(nil);
Bmp := TBitmap.Create;
try
Bmp.Canvas.Font.Assign(TControlAccess(Control).Font);
Bmp.Width := Bmp.Canvas.TextWidth(SNoDrop) + Margin;
Bmp.Height := Bmp.Canvas.TextHeight(SNoDrop);
Bmp.Canvas.TextOut(Margin, 0, SNoDrop);
FDragImages.Width := Bmp.Width;
FDragImages.Height := Bmp.Height;
FDragImages.Add(Bmp, nil);
Bmp.Canvas.FillRect(Rect(0, 0, Bmp.Width, Bmp.Height));
Bmp.Canvas.TextOut(Margin, 0, SDrop);
FDragImages.Add(Bmp, nil);
FDragImages.SetDragImage(0, 0, 0);
finally
Bmp.Free;
end;
end;
Result := FDragImages;
end;
{ TForm1 }
procedure TForm1.FormCreate(Sender: TObject);
begin
Grid1.ControlStyle := Grid1.ControlStyle + [csDisplayDragImage];
Grid2.ControlStyle := Grid2.ControlStyle + [csDisplayDragImage];
end;
procedure TForm1.Grid1StartDrag(Sender: TObject; var DragObject: TDragObject);
begin
DragObject := TMyDragControlObject.Create(Sender as TStringGrid);
end;
procedure TForm1.Grid2DragOver(Sender, Source: TObject; X, Y: Integer;
State: TDragState; var Accept: Boolean);
begin
Accept := False;
if IsDragObject(Source) then
with TMyDragControlObject(Source) do
if Control is TGrid then
{ Just some condition for testing }
if Y > Control.Height div 2 then
Accept := True;
end;
答案 1 :(得分:5)
作为NGLN pointed out,更改未生效的原因是Windows在拖动时创建临时图像列表。作为稍微不同的解决方案,您可以直接更改此临时列表中的图像。
以下是相应的修改后的DragOverPaint
。请注意,您仍然应该使用某种标志,以便在每次鼠标移动时不重新填充列表,如NGLN的答案。
procedure TForm1.DragOverPaint(ImageList: TImageList; AValue: string);
var
ABmp: TBitmap;
ImgList: HIMAGELIST; // <- will get the temporary image list
begin
if not Assigned(ImageList) then Exit;
ABmp := TBitmap.Create();
try
with ABmp.Canvas do begin
ABmp.Width := TextWidth(AValue);
ABmp.Height := TextHeight(AValue);
TextOut(0, 0, AValue);
end;
// ImageList.BeginUpdate; // do not fiddle with the image list,
// ImageList.Clear; // it's not used while dragging
// ImageList.Width := ABmp.Width;
// ImageList.Height := ABmp.Height;
// ImageList.AddMasked(ABmp, clNone);
// ImageList.EndUpdate;
// get the temporary image list
ImgList := ImageList_GetDragImage(nil, nil);
// set the dimensions for images and empty the list
ImageList_SetIconSize(ImgList, ABmp.Width, ABmp.Height);
// add the text as the first image
ImageList_AddMasked(ImgList, ABmp.Handle, ColorToRGB(clWhite));
finally
ABmp.Free();
end;
// Repaint; // <- No need to repaint the form
end;