Using the Command Handler Method in Delphi

Clients are very simple to implement, because they basically just send a request and process the response. Dropping an idTCPClient component on a form with a button, an edit box and a memo is basically all it takes to create a client. Once you connect the client to a server, all you do then is send a command and wait for a response from the server, which you display in the memo.

From our previous article we know that clients need a hostname or IP address and port number to connect to a server. So connecting to a client takes the form:

with IndyClient do begin

Host := 'myhostname.com' ; // You can use an IP Address here as well.

Port := 6000; //This is where the server is listening

Connect;

Try

// Read and write data here

finally

Disconnect;

end;

end;

The code above shows the minimum requirements for creating a client application:

• Set host property.
  
•  Set port property.
  
•  Connect.
  
•  Reading/Writing.
  
•  Disconnect.

We also need to consider exception handling. In most cases when using client-server applications, the server application will be located at a remote place. Since you don't know if the server is running or not, you should make provisions in your code for any exceptions that may result from the server being inactive. All indy exceptions are descended from EIdException:

try

IdTCPClient1

 try

// read/write here

finally IdTCPClient1

except

on E: EIdException do begin

ShowMessage('Indy Exception: ' + E.Message);

end else begin

ShowMessage('VCL Exception: ' + E.Message);

end;

end;