DataGridView列拖放使用自动滚动

Question

任何人都可以建议我如何在DataGridView中实现列拖放（带有自动滚动）功能。我知道我可以使用该控制器的允许词汇选项。但是，由于我的DataGridView控件具有相对较大的列，因此我需要一个自动滚动功能，该功能遵循当前的拖放位置，以便用户在掉落之前可以看到目标列。我已经实现了自定义拖放功能，但仍然有问题以启用自动滚动选项。

Answer 1

我正在使用以下类来自动浏览ttreeview。 TSCroller是在其坐在的框架的创建中创建的，并通过TreeView中的。它在框架的销毁中被摧毁。在TreeView的on Dragover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，则需要每个控件创建一个TSCroller。在这种情况下，使用某种类型的观察者/观测机制可以在所有滚动控件之间共享一个计时器。

Answer 2

您可以处理onmousemove，并相应地滚动。