Many of the properties of the server controls can be
conditioned with an indicator expression. The
conditional indicators on the DDS field or constant
are migrated to the
VisibleCondition property of the
corresponding control. The VisibleCondition property is
similar to the traditional
Visible property of ASPX controls in that it
determines whether the control is displayed or not.
Note however, that the Visible property is of type Boolean
while the VisibleCondition property is of type String. The
string is interpreted as a Condition, an expression involving
indicators and operators. The following are the syntax
elements used by indicator expressions:
- nn Test for Indicator nn
- & for AND
- | for OR
- ! for NOT
- () to specify operator precedence
For example, the equivalent of the following DDS sequence:
01 N02 03 A 04 O 05 06 O 07
Becomes this:
01 & !02 & 03 & 04 | (05 & 06) | 07
The DDS control list of conditional values are given at
design time but when the record is written to the
file, the list is processed from start to finish evaluating
the "condition" controlling the "value." As soon as a
condition is met, the associated value is used for the
property. Take for example the color property. It could
be assigned the color Red if indicator 17 was on,
or Black if not. The state of the indicators in
the AVR program at the time the record is written is used to
evaluate the conditional expressions. The
Monarch Web Control Indicator Expression
Tester Utility can be used
to test indicator expressions before changing
properties and compiling and testing the application where
the Display File is being used.
The use of parenthesis can specify an order of
precedence in the evaluation of the expression. This is
particularly useful when migrating DDS "Non display
Attribute, DSPATR(ND)". Using DSPATR(ND), when
the indicator expression is True, the control
is NOT displayed. In AVR, the VisibleCondition
evaluating True causes the control to
be displayed, which is not correct in the case of the
non-display attribute. Because of this, the legacy
source is migrated as a negation using "!" and
parenthesis around the whole indicator expression to simplify
the understanding and maintenance of the migrated Display
File. For example, if the above DDS sequence was
applied to a non-display attribute, the migrated VisibleCondition would contain !(01 & !02 & 03 &
04 | (05 & 06) | 07).
Condition Expression
A
condition is an expression involving indicators and operators as
explained above. The special values
*True,
*False, and *
None can be used in place of an
indicator.
| Syntax | Expression |
|---|---|
| Example | 03 & !99 |
| Meaning | True if *IN03 is *ON and *IN99 is *OFF; otherwise false. |
Conditional Value
A Conditional Value is a value followed by a colon and then a condition. It is possible to omit either the Value or Condition, but not both. If necessary, the Value should be enclosed in quotes.
| Syntax | Value : Condition |
|---|---|
| Example | Red: 03 & !99 |
| Meaning | The value Red is selected if *IN03 is *ON and *IN99 is *OFF |
Conditional Property
A Conditional Property is an array of comma separated Conditional Values.
| Syntax | Conditional value, Conditional value, Conditional value... |
|---|---|
| Example | Red : 03 & !99, Green : 06, Blue : 05 | 03 |
| Meaning | The value
Red is selected if *IN03 is *ON and
*IN99 is *OFF
otherwise, the value Green is selected if *IN06 is *ON otherwise, the value Blue is selected if *IN05 or *IN03 are *ON |
Conditional Properties
Conditional properties are utilized when specific properties are set. Classes are also provided to contain these property settings.
Attention Keys and Function Keys
In addition to the properties above, a special note must be made regarding AttnKeys and FuncKeys properties. These properties may be set once for the file, DdsFile.AttnKeys and DdsFile.FuncKeys, and once for the record, DdsRecord.AttnKeys and DdsRecord.FuncKeys. The keys aggregate across record formats active on the file when going to the browser.
These keys must be declared as part of each DdsFile, DdsRecord, or DdsSubfile where they are used in addition to being called by DdsButtons or similar controls.
AttnKeys and FuncKeys properties are semi-colon separated arrays representing:
FKEY 'Text' Conditional Property
Where FKEY is the function key, 'Text' is an optional
description for the key, and Conditional Property is as
described above or the special value *NONE. For instance, the following are two valid examples.
F3 'Add'; F4 'Delete' F3 'Add' 07:!99 ; F4 'Delete' *NONE:09