Handling Errors by Using Try Functions
Try functions in C/AL enable you to handle errors that occur in the application during code execution. For example, with try functions, you can provide more user-friendly error messages to the end user than those thrown by the system. You can use try functions to catch errors/exceptions that are thrown by Microsoft Dynamics NAV or exceptions that are thrown during .NET Framework interoperability operations. Try functions catch errors similar to a conditional Codeunit.Run function call, except with the following differences:
Try function calls do not require that write transactions are committed to the database.
Changes to the database that are made with a try function are not rolled back.
Before you use try functions in an application, read more about their usage at NAV Design Pattern: TryFunction – .NET Exception Handling in C/AL.
Creating a Try Function
To create a try function, add a function in C/AL code of an object (such as a codeunit) as usual, and then set the TryFunction property to Yes. A try function has the following restrictions:
The try function cannot have a user-defined return value.
Understanding Try Function Behavior and Usage
A function that is designated as a try function has a Boolean return value (true or false). A try function has the construction
If a try function call does not use the return value, the try function operates like an ordinary function and errors are exposed as usual.
If a try function call uses the return value in an
OK:=statement or a conditional statement such as
IF-THEN, errors are caught.
The return value is not accessible within the try function itself.
You can use the GETLASTERRORTEXT Function to obtain errors that are generated by Microsoft Dynamics NAV. To get details of exceptions that are generated by .NET Framework objects, you can use the GETLASTERROROBJECT to inspect the Expection.InnerException property.
The CRONUS International Ltd. demonstration database includes codeunit 1291 DotNet Exception Handler that includes several global functions for handling exceptions similar to a try-catch capability in C#. You can use this codeunit together with try functions to handle exceptions and maximize the reuse of code.
The following example illustrates the use of a try function together with codeunit 1291 DotNet Exception Handler to handle .NET Framework Interoperability exceptions. The code is in text file format and has been simplified for illustration. The
CallTryPostingDotNet function runs the try function
TryPostSomething in a conditional statement to catch .NET Framework Interoperability exceptions. Errors other than
IndexOutOfRangeException type are re-thrown.
[TryFunction] PROCEDURE TryPostingSomething@1(); BEGIN CODEUNIT.RUN(CODEUNIT::"Purch.-Post"); END; PROCEDURE CallTryPostingDotNet @2(); VAR MyPostingCodeunit@1 : Codeunit 90; MyDotNetExceptionHandler@2 : Codeunit 1291; IndexOutOfRangeException@3 : DotNet 'mscorlib, Version=188.8.131.52, Culture=neutral, PublicKeyToken=b77a5c561934e089'.System.IndexOutOfRangeException' BEGIN IF TryPostingSomething THEN MESSAGE('Posting succeeded.') ELSE BEGIN MyDotNetExceptionHandler.Collect; IF MyDotNetExceptionHandler.TryCastToType(IndexOutOfRangeException) THEN MESSAGE('The index used to find the value was not valid.') ELSE MyDotNetExceptionHandler.Rethrow; END; END;