Handling errors from Modify and
Describe methods in PowerBuilder
In PowerBuilder, no runtime error occurs when Describe and
Modify try to access invalid controls or properties in the DataWindow
object. The validity of the argument string is evaluated before the
controls are accessed.
Modify
When the string that specifies the control and property to be
accessed is invalid, Modify returns an error string, instead of the
expected value, such as:
|
1 |
Line 1 Column 12: incorrect syntax. |
You can use the error message to figure out what part of the
string is incorrect. This is most useful when you are testing your
scripts. The error message, which names the line and column number after
which the string was not recognized, might not be helpful after your
application is deployed.
Describe
When the string for Describe has an unrecognized property,
Describe’s return value ends with an exclamation point (!).
Describe returns as many values as it recognizes up to the incorrect
one.
When you specify a valid property but that property doesn’t have a
value (either because it hasn’t been set or because its value is an
expression that can’t be evaluated), Describe returns a question mark
(?) for that property. The property’s actual value is null.
Always check for errors
You should include error-checking code that checks for these
return values. Other errors can occur later if you depend on settings
that failed to take effect.
For more information
For more information on syntax and usage, see Describe and Modify
in Methods for the
DataWindow Control