delphi如何实现查看局域网在线主机

如题，如何看都有那些主机在线，用DELPHI编写

答案：
利用PING命令探测比较方便
以下代码稍微修改即可
在Delphi中使用TidIcmpClient控件可以非常简单的实现图形界面的Ping！
新建一个工程，命名为PingGUI.dpr，窗口命名为“frmPing”，加入如下组件：
    lstReplies: TListBox;
    ICMP: TIdIcmpClient;
    Panel1: TPanel;
    btnPing: TButton;
    edtHost: TEdit;
    spnPing: TSpinEdit;
    Label1: TLabel;
完整源代码如下：
unit Main; 
interface
uses
  Windows, Messages, Graphics, Controls, Forms, Dialogs, StdCtrls, ExtCtrls,
  SysUtils, Classes, IdIcmpClient, IdBaseComponent, IdComponent, IdRawBase, IdRawClient,
  Spin;

type
  TfrmPing = class(TForm)
    lstReplies: TListBox;
    ICMP: TIdIcmpClient;
    Panel1: TPanel;
    btnPing: TButton;
    edtHost: TEdit;
    spnPing: TSpinEdit;
    Label1: TLabel;
    procedure btnPingClick(Sender: TObject);
    procedure ICMPReply(ASender: TComponent; const ReplyStatus: TReplyStatus);
  private
  public
  end;
var
  frmPing: TfrmPing;
implementation
{$R *.DFM}
procedure TfrmPing.btnPingClick(Sender: TObject);
var
  i: integer;
begin
  ICMP.OnReply := ICMPReply;
  ICMP.ReceiveTimeout := 1000;
  btnPing.Enabled := False; try
    ICMP.Host := edtHost.Text;
    for i := 1 to spnPing.Value do begin
      ICMP.Ping;
      Application.ProcessMessages;
    end;
  finally btnPing.Enabled := True; end;
end;
procedure TfrmPing.ICMPReply(ASender: TComponent; const ReplyStatus: TReplyStatus);
var
  sTime: string;
begin
  // TODO: check for error on ping reply (ReplyStatus.MsgType?)
  if (ReplyStatus.MsRoundTripTime = 0) then
    sTime := <1
  else
    sTime := =;
  lstReplies.Items.Add(Format(%d bytes from %s: icmp_seq=%d ttl=%d time%s%d ms,
    [ReplyStatus.BytesReceived,
    ReplyStatus.FromIpAddress,
    ReplyStatus.SequenceId,
    ReplyStatus.TimeToLive,
    sTime,
    ReplyStatus.MsRoundTripTime]));
end;
end.

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