Hi everybody
On the last post I have mentioned about 6 events
which application objects does have. Today we are going to see briefly about those
six events
-----------------------------------------
The six Main events of Application Object are
1. Open
2.
Connectionbegin
3.
ConnectionEnd
4.
Close
5.
Idle
6.
SystemError
1.
Open
This
is main and very important event in the powerbuilder. Without this event we can’t
run any of our application. Whatever the project we are doing and in that
project which window should be appear first that information should be coded on
here. The first window to opened in the project to and if any database is used
in that project means, then we want to mention the DB connection in this open
event.
Ex:
Open(w_main)
This is the code, to open the w_main window first
when the project gets run
Ex.
SQLCA.DBMS = "OLE DB"
SQLCA.AutoCommit
= False
SQLCA.DBParm =
"PROVIDERSTRING='Database=DBNAME;Trusted_connection=yes;', PROVIDER='SQLOLEDB',
DATASOURCE='SERVER NAME',DelimitIdentifier='Yes',StaticBind='No'"
CONNECT
USING SQLCA;
(DONT GET CONFUSED ABOUT THIS CODE , THIS WILL BE
EXPLAINED IN NEXT POST)
This is the code to connect the database.
Now we have know about what should be written on
Open Event of the Application Object
In technical terms open event is described as “Occurs
when the user starts the application”.
2.
Connectionbegin
This
event is used for specifying the connection parameters that is used to connect
the database. We can do this connection at open event also. But this event is
the proper place to code the connection parameters. But most of the times
developers do coding at open event itself. This event is mainly used in client
server applications, where the initial connectivity is done by open event. And
later when client tries to access the server this connection begins will be
triggered and connection is established.
This event is technically described
as
In a distributed
computing environment, occurs on the server when a client establishes a
connection to the server by calling the ConnectToServer function.
3.
ConnectionEnd
As
explained in above, every time a client connects to the server, ConnectionBegin
event is fired at the server. When the process is done, then its gets
disconnects from the server, so at the time of this process the code returned
in the connection End will be get executed.
In
real times most of the developers won’t use these Events because of some error
handling problems. Instead they will utilize the Open and Close events
This
event is technically described as
In a distributed
computing environment, occurs on the server when a client disconnects from the
server by calling the DisconnectServer function.
4. Close
This is the most used event in
application object. This event is used also for the alternative of ConnectionEnd
Event. When the project work is done ,
all the process are completed then the used is going to close the project means
at the time if we want to do and operations or want to throw any
message/information/Error means we can code that codes in this event. Also the
database disconnect coding are coded here. We can also prevent the closing of
project by UN accidental way by asking the user to confirm the close.
Ex:
IF
MessageBox("Closing window", "Are you sure?", Question!,
YesNo!) = 2 THEN
RETURN 1
ELSE
RETURN 0
END IF
5. Idle
The application is started and is in
at running stage, if the used not interact with the application for the certain
amount of time then we want the application to be got locked, like this kind of
scenarios idle event is used.
If there is no interaction with the
application for the particular amount time then the idle event is executed.
Ex:
Idle(300) // Sends an
Idle event after 5 minutes.
6. SystemError
When
the application is at running if any undetermined/uncaught error occurred and
that is not handled in coding means then powerbuilder throws and error and
exits the application. We can prevent this unexpected error and closing of
application by coding on this event and ask the user to close or not. We can
use try – catch to implement error handling in this event.
Technically described as
Displays system errors and allows
the user to either continue running the application, exit the application, or
print the error message.
Ex:
Messagebox
("Error","errornum"+string(error.number)+ &
"message"+error.text+
&
"where"+error.windowmenu+
&
"object"+error.object+
&
"event" +error.objectevent+ &
"line"+string(error.line))
As for as now we have learned about
the application object and events of the application object and when to use
which event. Try to do some practicals like last post. We will see at next
post.
Regards
Pushparaj
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