Check whether the error messages load properly in the d_definedmessages. By any reason if it doesn�t, and an error occurs in the application, it might go into a loop and the program might get aborted.
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Good applications define standard error messages for possible errors, that are known at the design time. Each message is assigned a message id and a severity number. This allows reading of the error message using the error number at run-time. Severity number defines the seriousness of the message. For example, in Sybase SQL Server, messages with severity level below 16 are informational. You may allow the user to continue if the severity level is below certain number. All these defined messages are stored either in a text file or in a database. All developers use these standard messages with parameters. There are two advantages of this method over hard-coding error messages in the program.
For example, to display an error message about a non-existing product, you can define a message something like:
Product No # %n is not existing in the database.
The percentage sign indicates the position of the parameter. Systems like Sybase SQL Server use different characters after the percentage sign, depending on the data type of the parameter being placed there. Say �n� for numbers, �s� for strings and so on. However, PFC uses �s� for all data types.
When you store the error messages in the text/database, you should use the following format.
To store the messages in a text file with no problems, open the d_definedmessages DataWindow, and enter the data and export it as text with no headers.
Check whether the error messages load properly in the d_definedmessages. By any reason if it doesn�t, and an error occurs in the application, it might go into a loop and the program might get aborted.
Now let�s see how we can use the text file/database as an error messages source. First, let�s start with the text file. You need to call the following function, either from the pfc_Open or constructor event of the n_cst_AppManager object.
inv_Error.of_SetPredefinedSource("err-msg.txt")
PFC uses a DataStore object with the d_definedmessages DataWindow object. When you call this function, PFC loads all the messages in the DataStore object. If you decide to use the database in place of the text file, then don�t make the above call, instead use the following (actually, the above function is overloaded). Before you write the following code, declare an instance variable itr_error of type n_tr at the n_cst_AppManager.
n_tr itr_error
Write the following to the pfc_Open event of the n_cst_AppManager object.
Integer li_rc
itr_Error = CREATE n_tr
li_rc = itr_Error.of_Init(of_GetAppINIFile(), "ErrorDB")
If li_rc <> 1 Then
MessageBox("Error", &
"Error Transaction Object failed " + &
"initialization. ~nThis stops the application.", &
StopSign!, OK!, 1)
This.Event Post pfc_exit()
Return
End If
li_rc = itr_Error.of_Connect()
If li_rc <> 0 Then
MessageBox("Error", &
"Error while connecting to the " + &
"error database. ~nThis stops the application.", &
StopSign!, OK!, 1)
This.Event Post pfc_exit()
Return
End If
li_rc = inv_Error.of_SetPredefinedSource(itr_Error)
If li_rc <> 1 Then
MessageBox("Error", &
"Error while setting the error " + &
" info source.~nThis stops the application.", &
StopSign!, OK!, 1)
This.Event Post pfc_exit()
Return
End If
In the above code, we are creating a transaction object of type n_tr. The use of this transaction object is to connect to the database that has the "messages" table. After that, we are populating the transaction object with the database specific information to connect to the database. The of_GetAppINIFile() function returns the applications INI file name and of_Init() is available at the error service object n_cst_error. This function reads the specified section and populates the transaction object. Then, we are calling of_Connect() to connect to the database. Once the connection is successfully, we are calling of_SetPredefinedSource() to load all the messages in the DataStore object.
The setup process installs the ODBC entries for the PFC database. If you go to the database painter, you can see the entries for the PFC database in the ODBC configuration manager. However, we need to provide details in the application INI file as shown below, otherwise, PowerBuilder won�t be able to connect to the PFC database.
[ErrorDB]
DBMS=ODBC
Database=pfc
UserID=DBA
DatabasePassword=SQL
DBParm=ConnectString='DSN=pfc'
Now, if you test the application with the above error, PowerBuilder uses the default message id pfc_SystemError and the message box looks like:
Actually, you see only one button OK. We have changed it in our database that�s why you see three buttons in the above picture. We will explain about sending parameters for the defined messages in the next session.
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