Can we use boolean operator in Delphi XE2 LiveBinding expression?

3
votes

I am planning to write a Live Binding source expression for TCheckBox:

SourceExpression = '(Checked = False) and (Enabled = True)'

When execute the code, an exception prompted:

Expected EOF - trailing text in expression

Is Delphi XE2 Live Binding support boolean operator?

1
delphidelphi-xe2livebindings
Just a wild guess - have you tried to use SourceExpression = '(not Checked) and (Enabled)' ? And why ? Because it hurts my eyes whenever I see = in boolean expression :-) But don't have Delphi XE2 right now... – TLama
not Checked is not supported, so I use Checked = False – Chau Chee Yang
Look at this SO question: How to write live binding expression that control TEdit.PasswordChar based on TCheckBox.Checked?. The accepted answer registers a boolean expression evaluator. – LU RD
AFAIK you can't use the logical operators (and, or, ´not´ , ´xor´, ´shl´, ´shr´) in a LiveBinding expression :(, as workaround you can register a custom method to evaluate the logical operation. – RRUZ
shl and shr are not logical operators. It's impossible to believe that live bindings don't support logical operators. – David Heffernan

1 Answers

1
votes

No, boolean operators are not supported directly.

From the docu:

You can use the following math symbols in your expressions:

  • Constants: nil True False Pi
  • Arithmetic operators: + - * /
  • Logic operators: = <> < <= > >=
  • Parentheses, (), to change operator precedence.

But you can use the builtin functions IfAll(), IfAny() and IfThen() instead of and, or and not:

SourceExpression := 'IfAll(IfThen(Checked, False, True), Enabled)'

Or you register your own functions.

I tested this 4 XE4, but it should work for XE2 2.

  • A or B: IfAny(A, B)
  • A and B: IfAll(A, B)
  • not A: IfThen(A, False, True)
  • A xor B: IfAll(IfAny(A, B), IfThen(IfAll(A,B), False, True))