Question

任何人都可以建议我应该如何在DataGridView中实现列拖放（使用自动滚动）功能。我知道我可以使用controll的AllowUserToDragDrop选项。但是，由于我的datagridview控件具有相对较多的列，我需要一个自动滚动功能，该功能遵循当前的拖放位置，以便用户可以在删除之前查看目标列。我已经实现了自定义拖放功能，但我仍然遇到启用自动滚动选项的问题。

Answer 1

我使用以下类自动滚动TTreeView。 TScroller在它所在的框架的创建中创建，传递TreeView。它在框架的毁灭中被摧毁。在TreeView的OnDragOver中，我只需调用MyDragScroller.Scroll（State）;

type
  TScroller = class(TObject)
  private
    MyTimer: TTimer;
    FControl: TWinControl;
    FSensitiveSize: Integer;
  protected
    procedure HandleTimer(Sender: TObject);
  public
    constructor Create(aControl: TWinControl);
    destructor Destroy; override;

    procedure Scroll(const aState: TDragState);
  end;

implementation

{ TScroller }

constructor TScroller.Create(aControl: TWinControl);
begin
  inherited Create;
  MyTimer := TTimer.Create(nil);
  MyTimer.Enabled := False;
  MyTimer.Interval := 20; // Not too short, otherwise scrolling flashes by.
  MyTimer.OnTimer := HandleTimer;

  FControl := aControl;
  // Width/Height from edge of FControl within which the mouse has to be for
  // automatic scrolling to occur. By default it is the width of a vertical scrollbar.
  FSensitiveSize := GetSystemMetrics(SM_CXVSCROLL);
end;

destructor TScroller.Destroy;
begin
  FreeAndNil(MyTimer);
  FControl := nil;
  inherited;
end;

procedure TScroller.HandleTimer(Sender: TObject);
var
  MousePos: TPoint;
  MouseX: Integer;
  MouseY: Integer;

  function _MouseInSensitiveSize: Boolean;
  begin

    MousePos := FControl.ScreenToClient(Mouse.CursorPos);
    MouseY := MousePos.Y;
    MouseX := MousePos.X;

    Result :=
         ((MouseY >= 0) and (MouseY < FSensitiveSize))
      or ((MouseY > FControl.ClientHeight - FSensitiveSize) and (MouseY <= FControl.ClientHeight))
      or ((MouseX >= 0) and (MouseX < FSensitiveSize))
      or ((MouseX > FControl.ClientWidth - FSensitiveSize) and (MouseX <= FControl.ClientWidth))
    ;

  end;
begin
  if Mouse.IsDragging and _MouseInSensitiveSize then begin
    if MouseY < FSensitiveSize then begin
      FControl.Perform(WM_VSCROLL, SB_LINEUP, 0);
    end else if MouseY > FControl.ClientHeight - FSensitiveSize then begin
      FControl.Perform(WM_VSCROLL, SB_LINEDOWN, 0);
    end;

    if MouseX < FSensitiveSize then begin
      FControl.Perform(WM_HSCROLL, SB_LINELEFT, 0);
    end else if MouseX > FControl.ClientWidth - FSensitiveSize then begin
      FControl.Perform(WM_HSCROLL, SB_LINERIGHT, 0);
    end;
  end else begin
    MyTimer.Enabled := False;
  end;
end;

procedure TScroller.Scroll(const aState: TDragState);
begin
  if not Mouse.IsDragging then Exit;  // Only scroll while dragging.
  if not (aState in [dsDragMove]) then Exit; // No use scrolling on a dsDragLeave and not nice to do so on a dsDragEnter.

  MyTimer.Enabled := True;
end;

注意：如果您有更多需要自动滚动的控件，则需要为每个控件创建一个TScroller。在这种情况下，使用某种观察者/观察到的机制在所有滚动控件之间共享计时器可能会对你的应用程序的性能有很大帮助。

Answer 2

您可以处理OnMouseMove，并以编程方式相应地滚动。

DataGridView使用自动水平滚动拖放列

2 个答案: