if not Assigned(Modeless) then
Assigned()什么意思！
最佳答案
assigned 是用来判断某一指针(pointer)或过程引用是否为nil(空)，如果为空则返回假（false）。
用法示例(防止窗体被实例化多次)：
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;
type
TForm1 = class(TForm)
Button1: TButton;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
uses Unit2;
{$R *.dfm}
procedure TForm1.Button1Click(Sender: TObject);
begin
if (Not assigned(form2)) then
begin
form2:=Tform2.Create(Self);
end;
form2.show;
end;
end.
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unit Unit2;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
messages什么意思Dialogs;
type
TForm2 = class(TForm)
procedure FormClose(Sender: TObject; var Action: TCloseAction); private
{ Private declarations }
public
{ Public declarations }
end;
var
Form2: TForm2;
implementation
{$R *.dfm}
procedure TForm2.FormClose(Sender: TObject; var Action: TCloseAction); begin
Action:=caFree;
form2:=nil; //这句比较重要，窗体被释放时，窗体变量并不会自动变空end;
end.

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