Print Messages using info, warning and error

Print Messages using info(), warning() and error() in X++

Overview

Dynamics 365 Finance and Operations talks to users through the Infolog, the message bar at the top of every page. X++ gives you three global functions for writing to it, one per severity level: info(), warning() and error(). This program calls each one once so you can see how the three messages look side by side.

Choosing the right level matters in real projects. Users ignore screens full of red errors that are only informational, and they miss real problems shown in blue. Knowing what each function does, and what it does not do (none of them stops your code), is one of the first things every X++ developer must learn.

Prerequisites

• A D365 F&O development environment with Visual Studio, and a model and project to work in.
• A runnable class: Add > New Item > Dynamics 365 Items > Code > Runnable Class (Job). The class name must match the file name.
• No tables or setup data are needed.

Code Walkthrough

1. The class declaration

internal final class PrintMessages

internal keeps the class inside its own model and final stops other classes from extending it. Both are good defaults for runnable demo classes.

2. The information message

info("This is an information message.");

info() writes a blue message with an "i" icon. Use it to confirm success, for example "Invoice posted" or "15 records updated".

3. The warning message

warning("This is a warning message.");

warning() writes a yellow message with a triangle icon. Use it when something is unusual but processing can continue, for example "Customer is close to the credit limit".

4. The error message

error("This is an error message.");

error() writes a red message with a cross icon. The important point is that calling error() on its own does not stop the program. The next statement still runs. To stop execution and roll back the current transaction you must throw it:

• throw error("Amount cannot be negative."); stops the code and raises an Exception::Error.
• error() returns the value Exception::Error, which is exactly what throw needs. That is why throw error("...") works as one statement.

Key Concepts

• Infolog: the global message collector. Messages are gathered while the code runs and shown when control returns to the client.
• Severity levels: info (blue), warning (yellow), error (red). The level also controls filtering in the Infolog pane.
• throw: turns a message into an exception. Use throw error() for real errors and catch it with try/catch (Exception::Error).
• checkFailed(): writes a warning and returns false. It is the standard way to report a failed check inside validateWrite() or validateField().
• setPrefix(): groups related messages under a heading in the Infolog tree, which is very useful in batch jobs.

Expected Output

This is an information message.
This is a warning message.
This is an error message.

The Infolog shows three lines with different icons and colours: blue for info, yellow for warning and red for error. Because an error message is present, D365 F&O opens the message bar in its error style.

Best Practices and Common Mistakes

• Do use throw error("..."), not just error("..."), when the process must stop.
• Do use labels (for example "@MyModel:CreditLimitExceeded") for messages users will see, so they can be translated.
• Do include useful detail, such as the record ID: strFmt("Customer %1 is blocked", custAccount).
• Do not use error() for messages that are just informational. Red messages make users think something failed.
• Do not write thousands of messages in a loop. The Infolog has a limit of about 10,000 lines and large logs slow the client.
• Remember that in batch jobs, Infolog messages are saved to the batch job history, so meaningful messages help support teams.

Interview Questions

1. Does error() stop code execution?
   No. It only writes a red message. Use throw error("...") to stop execution and roll back the transaction.
2. What is the difference between warning() and checkFailed()?
   Both write a warning, but checkFailed() also returns false, so it fits validation methods that return a boolean.
3. How do you group messages in the Infolog?
   Use setPrefix("Heading"). Messages written afterwards appear under that heading in the Infolog tree.
4. How do you clear the Infolog from code?
   Call infolog.clear(). Use it carefully, because it removes messages users may need.
5. What exception type does throw error() raise?
   Exception::Error, which you catch with catch (Exception::Error).