delphi 中 as 和 is 的使用

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;

type
TForm1 = class(TForm)
    Edit1: TEdit;
    Edit2: TEdit;
    Edit3: TEdit;
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
private
    { Private declarations }
public
    { Public declarations }
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var i:Integer;
begin
   for i:= 0 to ControlCount - 1 do
   begin
      if Controls[i] is TEdit then
        if (Controls[i] as TEdit).Text <> ‘‘ then
        begin
            (Controls[i] as TEdit).Text := ‘haha‘;
        end;
   end;
end;

end.

窗体控件

Tedit 1、Tedit 2、Tedit 3、Tbutton