# 🛡️ Uniface 10.4: Return Values & Error Handling with activate

📊 Key Return Values

After calling an operation with activate, Uniface provides return values that help you assess the result and detect any errors.

$status – The Main Return Value

• > 0: Successful execution, value returned by the operation.
• 0: No value assigned or no return statement present.
• < 0: An error occurred; details are in $procerror.
• 9: User exited the form with ^ACCEPT.
• 10: User exited the form with ^QUIT.

Code Example:

activate "MyCpt".do_it()
if ($status < 0)
    message "Error: " + $procerror
endif

---

🚨 Error Handling with $procerror

If an error occurs, $procerror contains a specific error code. The most important codes:

Error Code	Meaning
-50	Component not found
-59	Operation not defined
-1122	Wrong number of arguments
-155	Instance could not be created
...	See documentation for more

Code Example:

activate "MyCpt".do_it()
if ($status < 0)
    selectcase $procerror
        case -50
            message "Component not found!"
        case -59
            message "Operation does not exist!"
        case -1122
            message "Wrong number of arguments!"
        case else
            message "Unknown error: " + $procerror
    endselectcase
endif

🧰 Best Practices

• Always check $status and $procerror: Evaluate these values after every activate call.
• Provide meaningful error messages: Use error codes to give targeted feedback.
• Avoid negative return values: In your own operations, avoid returning negative values, as Uniface interprets them as errors.

🕵️‍♂️ Common Pitfalls

• Wrong arguments: Number or type does not match the operation’s parameters.
• Incorrect instance or operation name: Typos lead to -50 or -59.
• Asynchronous calls: No OUT/INOUT parameters and no return value with /async.

📝 Example: Robust Error Handling

Code Example:

activate "MyService".calculate(100, 200)
if ($status < 0)
message "Error during call: " + $procerror
return
endif
message "Calculation successful! Result: " + $status

This post is based on the official Uniface 10.4 documentation and was created with AI support. For details, see the original documentation.