判断网络连接状态的有关问题(掉线、已连接)

判断网络连接状态的问题(掉线、已连接)
做个小程序想随时高效的判断网络是否 掉线 和 已经连接上 ，请问应该怎么处理？
网络上的答案就不要给了，全试了个遍，没一个考虑得全面且实用！
谢谢！

------解决方案--------------------
第一步

API IsNetworkAlive() 能返回当前网络连接状态。（仅连接状态哦）
NETWORK_ALIVE_LAN 内网OK
NETWORK_ALIVE_WAN 公网OK（仅限于类似ADSL拨号直连连接）

第二步
const ROUTE_TO_GOOGLE = $04040404;
GetBestInterface(ROUTE_TO_GOOGLE, @dwInterfaceIndex);
如果这个返回网络接口了，那说明有网卡可以通向Google，那基本说明网络OK了

第三步
还不放心的话，上PING吧
------解决方案--------------------
function Ping(IP:string):boolean; overload;//uses WinSock
function Ping(IP:string):Boolean;
const
IcmpVersion=102;
IcmpDLL='icmp.dll';
type
TIcmpCreateFile=function:THandle;stdcall;
TIcmpCloseHandle=function(IcmpHandle:THandle):Boolean;stdcall;
TIcmpSendEcho=function(IcmpHandle:THandle;
DestinationAddress:DWORD;
RequestData:Pointer;
RequestSize:Word;
RequestOptions:Pointer;
ReplyBuffer:Pointer;
ReplySize:DWord;
Timeout:DWord
):DWord;stdcall;
var
hICMPdll:HModule;// Handle for ICMP.DLL
hICMP:THandle;
IcmpCreateFile:TIcmpCreateFile;
IcmpCloseHandle:TIcmpCloseHandle;
IcmpSendEcho:TIcmpSendEcho;
wsa:TWSAData;
rep:array[1..128] of byte;
InAddr2:DWORD;//InAddr1: TInAddr;
phe:PHostEnt;// HostEntry buffer for name lookup
pac:PChar;
dwRet:DWORD;
bValidIP:Boolean;
begin
Result:=False;
try
if WSAStartup($101,wsa)<>0 then exit;
bValidIP:=False;
InAddr2:=0;
phe:=GetHostByName(PChar(IP));
if Assigned(phe) then
begin
pac:=phe^.h_addr_list^;
if Assigned(pac) then
begin
InAddr2:=LongInt(PLongInt(phe^.h_addr_list^)^);
bValidIP:=True;
end;
end;
if bValidIP then
begin
hICMPdll:=LoadLibrary(icmpDLL);
if hICMPdll>0 then
begin
@ICMPCreateFile:=GetProcAddress(hICMPdll,'IcmpCreateFile');
@IcmpCloseHandle:=GetProcAddress(hICMPdll,'IcmpCloseHandle');
@IcmpSendEcho:=GetProcAddress(hICMPdll,'IcmpSendEcho');
if (@ICMPCreateFile<>nil)and(@IcmpCloseHandle<>nil)and(@IcmpSendEcho<>nil) then
begin
hICMP:=IcmpCreateFile;
if hICMP<>INVALID_HANDLE_VALUE then
begin
dwRet:=IcmpSendEcho(hICMP,InAddr2,nil,0,nil,@rep,128,0);
Result:=(dwRet<>0);
// if hICMP<>INVALID_HANDLE_VALUE then
IcmpCloseHandle(hICMP);
end;
// if hICMPdll<>0 then
FreeLibrary(hICMPdll);
end;
end;
end;
finally
WSACleanup;
end;
end;