REGISTER CLIENT
REGISTER CLIENT ( clientName {; period}{; *} )
| Parameter | Type | Description | |
|---|---|---|---|
| clientName | Text | → | Name of the 4D client session |
| period | Integer | → | Ignored since version 11.3 |
| * | Operator | → | Local process |
This command is not thread-safe, it cannot be used in preemptive code.
Description
The REGISTER CLIENT command “registers” a 4D client station with the name specified in clientName on 4D Server, so as to allow other clients or eventually 4D Server (by using stored methods) to execute methods on it by using the EXECUTE ON CLIENT command. Once it is registered, a 4D client can then execute one or more methods for other clients.
Notes:
- You can also automatically register each client station that connects to 4D Server by using the “Register Clients at Startup...” option in the Preferences dialog box.
- If this command is used with 4D in local mode, it has no effect.
- More than one 4D client station can have the same registered name.
When this command is executed, a process, named clientName, is created on the client station. This process can only be aborted by the UNREGISTER CLIENT command.
If you pass the optional * parameter, the created process is local. 4D will automatically add the dollar sign ($) at the beginning of the process name. Otherwise, the process is global.
Compatibility Note: Since version 11.3 of 4D, the server/client communication mechanisms have been optimized. Now the server sends execution requests directly to the registered clients when necessary (technology "push"). The previous principle where clients queried the server periodically is no longer used. The period parameter is ignored if it is passed.
Once the command is executed, it is not possible to modify a 4D client’s name on the fly. To do so, you must call the UNREGISTER CLIENT command, then the REGISTER CLIENT command.
Example
In the following example, we are going to create a small messaging system that allows the client workstations to communicate between themselves.
- This method, Registration, allows you to register a 4D client and to keep it ready to receive a message from another 4D client:
//You must unregister before registering under another name
UNREGISTER CLIENT
Repeat
vPseudoName:=Request("Enter your name:";"User";"OK";"Cancel")
Until((OK=0)|(vPseudoName#""))
If(OK=0)
... // Don’t do anything
Else
REGISTER CLIENT(vPseudoName)
End if
- The following instruction allows you to get a list of the registered clients. It can be placed in the :
PrClientList:=New process("4D Client List";32000;"List of registered clients")
- The method 4D Client List allows you to recuperate all the registered 4D clients and those that can receive messages:
If(Application type=4D Remote Mode)
// the code below is only valid in client-server mode
$Ref:=Open window(100;100;300;400;-(Palette window+Has window title);"List of registered clients")
Repeat
GET REGISTERED CLIENTS($ClientList;$ListeCharge)
//Retrieve the registered clients in $ClientList
ERASE WINDOW($Ref)
GOTO XY(0;0)
For($p;1;Size of array($ClientList))
MESSAGE($ClientList{$p}+Char(Carriage return))
End for
//Display each second
DELAY PROCESS(Current process;60)
Until(False) // Infinite loop
End if
- The following method allows you to send a message to another registered 4D client. It calls the Display_Message method (see below).
$Addressee:=Request("Addressee of the message:";"")
// Enter the name of the people visible in the window generated by the
// On Startup database method
If(OK#0)
$Message:=Request("Message:") // message
If(OK#0)
EXECUTE ON CLIENT($Addressee;"Display_Message";$Message) // Send message
End if
End if
- Here is the Display_Message method:
var $1 : Text
ALERT($1)
- Finally, this method allows a client station to no longer be visible by the other 4D clients and to no longer receive messages:
UNREGISTER CLIENT
System variables and sets
If the 4D client is correctly registered, the OK system variable is equal to 1. If the 4D client was already registered, the command doesn’t do anything and OK is equal to 0.