Internet Access: Client Service - Code Explained
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Let's look at the code. The timer event is th most important in this case because it determines whether the client application is running or not:
procedure TService1.Timer1Timer(Sender: TObject);
var
handle,h: HWND;
begin
handle:= FindWindow('TForm1', 'iClient');
if handle > 0 then
begin
showmessage('found it!');
end
else
begin
//startup the app here. Shellexec
shellexecute(h,'open','c:\intertimer\client\iclient.exe',nil,nil,0);
end;
end;
The procedure first checks to see if a window with the caption "iClient" is active. This is done using the findwindow() function of the Windows API:
handle:= FindWindow('TForm1', 'iClient');
The result of the search is then stored in the "handle" variable. The next thing that we do is check to see if the handle contains any value:
if handle > 0 then
If the handle contains a value, then the client application is actually running, in which case we do nothing:
begin
//remove the showmessage function, its there for debugging purposes
showmessage('found it!');
end
If the handle does not contain any value, the client application is not running, so we start it up by using the shell API function called shellexecute():
else
begin
//startup the app here. Shellexec
shellexecute(h,'open','c:\intertimer\client\iclient.exe',nil,nil,0);
There might be a small issue with the shellexec function because it is not portable, so make sure that all the workstations use the Windows operating system.
The service execute function is responsible for activating the timer component. Without this procedure the timer, which is deactivated, will stay deactivated and will not check to see if the client application is running:
procedure TService1.ServiceExecute(Sender: TService);
begin
//activate the timer here
timer1.Enabled:=true;
The while loop simply ensures that the thread remains active. If it is not active, the timer is set to false or deactivated:
while not terminated do
servicethread.ProcessRequests(true);
timer1.Enabled:=false;
end;
Next: To Install/Uninstall the service >>
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