Attributes/Themes evaluated regardless of conditionals?

[broconne]

I am seeing some behavior which I can't quit figure out but seems that attributes and themes are evaluated regardless of the conditional to reach them? Is that correct?

For example:

if( Evaluates_To_True )
true
Do Something
else
attribute=Blah

Even if, the if clause evaluates to true, my attribute is being set. In my specific scenario this is inside a table, and the the attribute set to the result of a method call. The method call is now failing because an unexpected object is being passed in as the result of the conditional being ignored.

Has anyone seen this?

[GKusnick]

Widget evaluation is a multipass process. The first pass happens when the menu is loaded, and instantiates every widget in every branch, including all of their widget properties. In the case of Attribute widget values, or any widget property with a dynamic value (i.e. one set to =expression), those expressions are evaluated as part of the widget instantiation. Conditional evaluation kicks in only during the actual rendering pass (for blue UI widgets) or action pass (for green process chains).

Bottom line is that you have to be prepared for your property expressions to be evaluated regardless of any conditionals guarding them.

[broconne]

Originally Posted by GKusnick

Widget evaluation is a multipass process. The first pass happens when the menu is loaded, and instantiates every widget in every branch, including all of their widget properties. In the case of Attribute widget values, or any widget property with a dynamic value (i.e. one set to =expression), those expressions are evaluated as part of the widget instantiation. Conditional evaluation kicks in only during the actual rendering pass (for blue UI widgets) or action pass (for green process chains).

Bottom line is that you have to be prepared for your property expressions to be evaluated regardless of any conditionals guarding them.

Well that is just cruel :-)

[GKusnick]

One trick I sometimes use is to replace a property value with an expression like this:

=If(true, value, DebugLog("message"))

Keeping one eye on the console window then gives me a pretty good idea of when (and how often) that expression is getting evaluated.

(If you're not familiar with the console window, it's a real-time display of the debug log in a DOS window; see p. 230 of the V7 manual. I highly recommend enabling it for any Studio or Java plugin work.)

[broconne]

Will inner expressions of conditionals inside of a theme widget also be evaluated regardless of the result of the outer condition? My testing says yes, but I can't quite figure out why.

For example, inside my theme widget I have the following for fontcolor:

=If(tvbrowser_Episodes_IsEpisode(SeasonEpisode),If(tvbrowser_Episodes_IsRecording(SeasonEpisode), "0xFF0000",gColorBasicWhite),gColorBasicWhite)

It seems like that inner If is evaluated inside the theme widget even if the first if is false. Just trying to verify it will go through any widgets evaluate everything, regardless of conditions inside the widgets themselves?

[PLUCKYHD]

You could also just adjust your method to handle the first pass or invalid object(which is probably null). I did that will some of my calls and logged it to be sure it was only doing it on first pass.

Another thing before it bites you like it did me beforemenuload loads after the attribute widget pass and such as well.

[GKusnick]

Bear in mind that there's nothing magic about If(); it's just a normal API call. And like any Java method call, all arguments are evaluated before being passed in to the method (which in this case, just returns one and discards the other). In that sense, If() is not equivalent to Java's ?: operator.

Less obvious is the fact that && and || in widget expressions always evaluate both operands. They do not short-circuit as their Java or C counterparts do.

[tmiranda]

We should probably put together a list of the common "gotcha's" of studio programming. Probably every one of us has been bitten by the "multipass" behavior as well as the BeforeMenuLoad hook behavior.

Greg - I have a challenge for you I would love it if we had "lint" for Studio that would catch common errors and display warnings for not so obvious behavior. It's probably a tall order but it would REALLY help Studio developers.

[GKusnick]

Originally Posted by tmiranda

Greg - I have a challenge for you I would love it if we had "lint" for Studio that would catch common errors and display warnings for not so obvious behavior. It's probably a tall order but it would REALLY help Studio developers.

If you set preload_expression_cache=true in your properties file, Studio will do a syntax check on all expressions when the STV is loaded. This should catch most errors that can be detected mechanically.

For subtle errors of the sort we've been discussing in this thread (such as whether it's safe to evaluate both sides of a conditional) it would take some pretty hard-core program-flow analysis to detect those.

[tmiranda]

Originally Posted by GKusnick

For subtle errors of the sort we've been discussing in this thread (such as whether it's safe to evaluate both sides of a conditional) it would take some pretty hard-core program-flow analysis to detect those.

You're just the man for the job