Vérifier si le système est connecté à Internet

Méthode n°1
uses
StdCtrls,registry;

Function IsConnected : Boolean;
var
reg : TRegistry;
buff : dword;
begin
reg:= tregistry.Create ;
Reg.RootKey:=HKey_local_machine;
if reg.OpenKey('SystemCurrentControlSetServicesRemoteAccess',false) then
begin
reg.ReadBinaryData('Remote Connection',buff,sizeof(buff));
result := buff = 1;
reg.CloseKey ;
reg.Free ;
end;
end;

Métode n°2:

interface

uses Windows, SysUtils, Registry, WinSock, WinInet;

type
TConnectionType = (ctNone, ctProxy, ctDialup);
function ConnectedToInternet : TConnectionType;
function RasConnectionCount : Integer;

implementation

//For RasConnectionCount =======================

const
cERROR_BUFFER_TOO_SMALL = 603; cRAS_MaxEntryName = 256;
cRAS_MaxDeviceName = 128;
cRAS_MaxDeviceType = 16;

type
ERasError = class(Exception);
HRASConn = DWord;
PRASConn = ^TRASConn;
TRASConn = record
dwSize: DWORD;
rasConn: HRASConn;
szEntryName: Array[0..cRAS_MaxEntryName] Of Char;
szDeviceType : Array[0..cRAS_MaxDeviceType] Of Char;
szDeviceName : Array [0..cRAS_MaxDeviceName] of char;
end;

TRasEnumConnections = function (RASConn: PrasConn; { buffer to receive Connections data }

var BufSize: DWord; { size in bytes of buffer }

var Connections: DWord { number of Connections written to buffer
}
): LongInt; stdcall;
//End RasConnectionCount =======================

function ConnectedToInternet: TConnectionType;
var
Reg : TRegistry;
bUseProxy : Boolean;
UseProxy : LongWord;

begin
Result := ctNone;
Reg := TRegistry.Create;
with REG do
try
try
RootKey := HKEY_CURRENT_USER;
if OpenKey('settings',False) then begin
//I just try to read it, and trap an exception
if GetDataType('ProxyEnable') = rdBinary then
ReadBinaryData('ProxyEnable', UseProxy, SizeOf(LongWord) )
else begin
bUseProxy := ReadBool('ProxyEnable');
if bUseProxy then
UseProxy := 1
else
UseProxy := 0;
end;
if (UseProxy <> 0) and ( ReadString('ProxyServer') <> '' ) then Result:= ctProxy;
end;
except
//Obviously not connected through a proxy
end;
finally
Free;
end;
//We can check RasConnectionCount even if dialup networking is not installed
//simply because it will return 0 if the DLL is not found.
if Result = ctNone then begin
if RasConnectionCount > 0 then Result := ctDialup;
end;
end;

function RasConnectionCount : Integer;
var
RasDLL : HInst;
Conns : Array[1..4] of TRasConn;
RasEnums : TRasEnumConnections;
BufSize : DWord;
NumConns : DWord;
RasResult : Longint;

begin
Result := 0;
//Load the RAS DLL
RasDLL := LoadLibrary('rasapi32.dll');
if RasDLL = 0 then exit;
try
RasEnums := GetProcAddress(RasDLL,'RasEnumConnectionsA');
if @RasEnums = nil then
raise ERasError.Create('RasEnumConnectionsA not found in rasapi32.dll');
Conns[1].dwSize := Sizeof (Conns[1]);
BufSize := SizeOf(Conns);
RasResult := RasEnums(@Conns, BufSize, NumConns);
If (RasResult = 0) or (Result = cERROR_BUFFER_TOO_SMALL) then Result := NumConns;
finally
FreeLibrary(RasDLL);
end;
end;