Using Design-time Constants in Expressions

Before an expression is evaluated, any design-time constants in it are replaced by the values they represent. If these values contain spaces (or other value-delimiting characters) they can cause the expression to produce unexpected results, and even generate errors at run time.

For instance, let's say we want to concatenate (i.e. join) the string " is a nice person" to the string contained in the constant #UserName#. We could use the expression:

#UserName# + " is a nice person"

...which works fine if the constant #UserName# contains a single word like Mark. But if #UserName# contains a space like, say, Mark Smark, the expression becomes:

Mark Smark + " is a nice person"

...which fails, because Mark and Smark are seen as two separate values with no operator between them. The space between Mark and Smark acts as a delimiter, "splitting" the words into two separate values. AutoPlay Media Studio expects to see Mark <operator> Smark, but the operator is missing, and the resulting "broken" expression generates an error.

In order to avoid these problems, it's a good idea to surround design-time constants with quotation marks when using them in expressions. Any value between quotes is always interpreted as a single value, regardless of any spaces or other delimiting characters it might contain. By putting quotes around constants, each constant is guaranteed to be seen as a single value.

So, if we rewrite our example expression as:

"#UserName#" + " is a nice person"

...we end up with:

"Mark Smark" + " is a nice person."

...which will not cause any problems.