DataGridView列拖放使用自动滚动
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04-10-2019 - |
题
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。
解决方案
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。
其他提示
您可以处理onmousemove,并相应地滚动。
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