如何将 MDI 子窗口拉出主窗体？

Question

我想创建一个带有自己的任务栏的 MDI 应用程序，以便用户可以快速访问他/她想要带到前面的子窗口。然后我想到一个使用两个或多个监视器的用户可以将子窗口从我的应用程序的主窗体内部拖到它的外部，例如，拖到另一个监视器中。

怎么做？

Answer 1

也许这个示例 MDI 客户端表单代码可以提供灵感：

unit Unit3;

interface

uses
  Windows, Messages, Controls, Forms;

type
  TForm3 = class(TForm)
  private
    FSizing: Boolean;
    procedure WMNCMouseLeave(var Message: TMessage);
      message WM_NCMOUSELEAVE;
    procedure WMWindowPosChanged(var Message: TWMWindowPosChanged);
      message WM_WINDOWPOSCHANGED;
  protected
    procedure CreateParams(var Params: TCreateParams); override;
    procedure Resize; override;
  end;

implementation

{$R *.dfm}

{ TForm3 }

var
  FDragging: Boolean = False;

procedure TForm3.CreateParams(var Params: TCreateParams);
begin
  inherited CreateParams(Params);
  if FormStyle = fsNormal then
    Params.ExStyle := Params.ExStyle or WS_EX_APPWINDOW
  else
    Params.ExStyle := Params.ExStyle and not WS_EX_APPWINDOW;
end;

procedure TForm3.Resize;
begin
  inherited Resize;
  FSizing := True;
end;

procedure TForm3.WMNCMouseLeave(var Message: TMessage);
begin
  inherited;
  FDragging := False;
end;

procedure TForm3.WMWindowPosChanged(var Message: TWMWindowPosChanged);
var
  P: TPoint;
  F: TCustomForm;
  R: TRect;
begin
  inherited;
  if not FDragging and not FSizing and not (fsShowing in FormState) and
    (WindowState = wsNormal) then
  begin
    F := Application.MainForm;
    P := F.ScreenToClient(Mouse.CursorPos);
    R := F.ClientRect;
    InflateRect(R, -5, -5);
    if not PtInRect(R, P) and (FormStyle = fsMDIChild) then
    begin
      FDragging := True;
      FormStyle := fsNormal;
      Top := Top + F.Top;
      Left := Left + F.Left;
    end
    else if PtInRect(R, P) and (FormStyle = fsNormal) then
    begin
      FDragging := True;
      FormStyle := fsMDIChild;
    end;
  end;
  FSizing := False;
end;

end.