Friday, 18 July 2008

Oracle ADF/ JSF: Mind your flags!

I do not know why JSF UI elements have a Disabled property. I mean I would prefer it if they instead offered an Enabled one. ADF bindings on the other hand have enabled properties, so UI tags usually look this :

<af:commandButton actionListener="#{bindings.Create.execute}"

How imagine having to wire in the UserInfo bean, I was talking about the other day. Ideally you would like to have the above Create button enabled when your user is an administrator i.e. #{UserInfo.admin == true} and when the Create binding is enabled, meaning #{bindings.Create.enabled == true}.

Since we now have a Disabled property, this means that the value assigned should be the opposite of #{UserInfo.admin == true && bindings.Create.enabled == true}. The EL expression for this is #{!(UserInfo.admin == true && bindings.Create.enabled == true)}. Using De Morgan's low we end up with #{!UserInfo.admin || !bindings.Create.enabled}.

I understand that for most people this is more than trivial, but I have to admit that is took me a good while to figure it out. (Does age come at a price or what?) I want to learn by my own mistakes. Therefore I thought I 'd put it down in witting, so I won't run into this again.


Chris Muir said...

Ha! I hear you. The new 11g accordion like controls have a property "disclosed" which of course when you take away the double negative means "open". So much easier to understand.


John Stegeman said...

Don't disable it if not the binding isn't enabled ;)

Agree with you wholeheartedly.