设计一个简易的文本编辑器，具有创建、编辑、保存普通文本文件的功能。 

unit U nit1;

interface

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

type
  TForm1 = class(TForm)
    Panel1: TPanel;
    Memo1: TMemo;
    OpenDialog1: TOpenDialog;
    SaveDialog1: TSaveDialog;
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    Button4: TButton;
    Button5: TButton;
    Button6: TButton;
    Button7: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
    procedure Button4Click(Sender: TObject);
    procedure Button5Click(Sender: TObject);
    procedure Button6Click(Sender: TObject);
    procedure Button7Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
var
  f:textfile;
  wfilename:string;
  flag:boolean;
 
implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
begin
  assignfile(f,'newfile.txt');
  form1.Caption:='newfile.txt';
  wfilename:='newfile.txt';
  rewrite(f);
  memo1.Enabled:=true;
  button1.Enabled:=false;
  button2.Enabled:=false;
  button3.Enabled:=false;
  button4.Enabled:=true;
  button5.Enabled:=true;
  button6.Enabled:=true;
  button7.Enabled:=true;
  closefile(f); 
end;

procedure TForm1.Button2Click(Sender: TObject);
var
  line:string;
begin
  if opendialog1.Execute then
    begin
      assignfile(f,opendialog1.FileName);
      reset(f);
      form1.Caption:=opendialog1.FileName;
      memo1.Enabled:=false;
      flag:=true;
      while not eof(f) do
        begin
          readln(f,line);
          memo1.Lines.Add(line);
        end;
      button1.Enabled:=false;
      button2.Enabled:=false;
      button3.Enabled:=false;
      button4.Enabled:=false;
      button5.Enabled:=false;
      button6.Enabled:=true;
      button7.Enabled:=true;
      closefile(f);
    end;
end;

procedure TForm1.Button3Click(Sender: TObject);
var
  line:string;
begin
  if opendialog1.Execute then
    begin
      wfilename:=opendialog1.FileName;
      assignfile(f,wfilename);
      form1.Caption:=wfilename;
      reset(f);
      memo1.Enabled:=true;
      while not eof(f) do
        begin
          readln(f,line);
          memo1.Lines.Add(line);
        end;
      button1.Enabled:=false;
      button2.Enabled:=false;
      button3.Enabled:=false;
      button4.Enabled:=true;
      button5.Enabled:=true;
      button6.Enabled:=true;
      button7.Enabled:=true;
      closefile(f);
    end;
end;

procedure TForm1.Button4Click(Sender: TObject);
var
  i,lastline:integer;
begin
  lastline:=memo1.Lines.Add('')-1;
  assignfile(f,wfilename);
  rewrite(f);
  for i:=0 to lastline do
    begin
      write(f,memo1.lines[i]);
    end;
  closefile(f);
end;

procedure TForm1.Button5Click(Sender: TObject);
var
  i,lastline:integer;
  writefile:textfile;
begin
  if savedialog1.Execute then
    begin
      wfilename:=savedialog1.FileName;
      assignfile(writefile,wfilename);
      rewrite(writefile);
      form1.Caption:=wfilename;
      lastline:=memo1.Lines.Add('')-1;
      for i:=0 to lastline do
        begin
          writeln(writefile,memo1.lines[i]);
        end;
      closefile(writefile);
    end;
end;

procedure TForm1.Button6Click(Sender: TObject);
var
  i:integer;
begin
   if not flag then
     i:=messagedlg('save file ?',mtConfirmation,mbYesNoCancel,0);
   if i <> 2 then
     begin
       if i=6 then
         Button4Click(sender);
       memo1.Clear;
       form1.Caption:='';
       memo1.Enabled:=false;
       button1.Enabled:=true;
       button2.Enabled:=true;
       button3.Enabled:=true;
       button4.Enabled:=false;
       button5.Enabled:=false;
       button6.Enabled:=false;
       button7.Enabled:=true;
     end;
   flag:=false;
end;

procedure TForm1.Button7Click(Sender: TObject);
begin
  close;
end;

end.