判断一个对象是否存在(赋值)的三种办法如下:
if obj <> nil then ...
if Boolean(obj) then ...
if Assigned(obj) then ...
通过下面的测试, 结论是 obj <> nil 最慢; Boolean(obj) 与 Assigned(btn) 相当!
测试图:
测试源码:
if obj <> nil then ...
if Boolean(obj) then ...
if Assigned(obj) then ...
通过下面的测试, 结论是 obj <> nil 最慢; Boolean(obj) 与 Assigned(btn) 相当!
测试图:
测试源码:
unit Unit1; interface uses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls; type TForm1 = class(TForm) Button1: TButton; procedure Button1Click(Sender: TObject); end; var Form1: TForm1; implementation {$R *.dfm} var btn: TButton; n: Cardinal; procedure TForm1.Button1Click(Sender: TObject); var i: Integer; begin n := GetTickCount; for i := 0 to 100000000 do if btn <> nil then ; n := GetTickCount - n; Text := IntToStr(n); n := GetTickCount; for i := 0 to 100000000 do if Boolean(btn) then ; n := GetTickCount - n; Text := Text + ' - ' + IntToStr(n); n := GetTickCount; for i := 0 to 100000000 do if Assigned(btn) then ; n := GetTickCount - n; Text := Text + ' - ' + IntToStr(n); end; end.