CE Display Rules C#

Hello, I'm trying to develop an add-in for creating Display Rules in c #. I have a problem creating the condition to pass as a parameter to the constructor of the DisplayRule class.
At this link "">www.bimsdks.com/.../structBentley_1_1DgnPlatform_1_1DisplayRule.html" I found some examples (see Condition format and types) but they are very few.

I implemented the following code that works:

string MyRuleCondition = @"element.IsOfClass (""ShapeElement"",""DgnElementSchema"")";

DisplayRuleSet displayRuleSet = new DisplayRuleSet(RuleStenName, dgnFile);
DisplayRulesManager.WriteDisplayRuleSetToFile(displayRuleSet, dgnFile, true);
DisplayRule displayRuleElement = new DisplayRule(MyRuleCondition, true, dgnFile);

IDisplayRuleAction ruleAction = new ColorOverrideAction(5, dgnFile);
DisplayRulesManager.WriteDisplayRuleSetToFile(displayRuleSet, dgnFile, true);



I should implement a RuleCondition that evaluates the value of a property of an ItemType,
does anyone know a way, a tool, or examples (in c #) to create RuleConditions?

Thanks for the help, greetings

Parents Reply
  • Hi salvatore,

    I was not able to figure how to determine the schema name of the ItemTypeLibary in the condition's expression.

    it's "simple" (when you know it :-) ). When you need to know intrinsict (stored in DGN file) EC schemas, and ItemTypes EC schemas are alwayas intrinsict, use "ecx schema list" key-in, that lists the schemas to Message Center Details.

    Graphical elements features like color etc. are defined in extrinsict EC schema DgnElementSchema.

    Since there is no match between the condition expression shown in the user's interface and the expression required in code

    There is no reason why there should be the match. It seems description is filled automatically by a summary, but it's not the condition syntax.

    I don't know how to write the condition's expression.

    Well ... as written in the documentation you linked: DisplayRule condition is based on ECExpression. I agree it tells nothing for a plain user, and also for developers it's not clear for 100% (because "is based on" expresses that it's only a subset of ECExpression). But at least, it's defines the basic syntax format.

    Is there a reference guide describing the schemas and the expression syntax?

    I think the description provided in DisplayRule API documentation is where you should start. Despite of it's short, I think it covers the most of needs and scenarios.

    Two other sources are:

    • Search this web (and Internet in general) for ECExpression. Because this technology has existed in Bentley products for many (maybe 15?) years already, it's possible to fined some valuable blogs and articles (e.g. this one). But be aware it's not specified that Display Rules support complete ECExpression (plus some features of ECE are not conditions).
    • Read how conditions are defined in Item Types (now in Technology Preview phase), because they are, again, ECExpressions.

    The problem is that without good knowledge of the whole "EC world" (which is very wide and complex topic), some concepts behind and terminology will remain unexplained.

    With regards,


  • the link


    doesn't exist?  Just goes to Bentley docs.
    Can you give the proper link or is this another link only available to Bentley employees?
    Which Bentley Doc lists the Beta Expressions?

    Display rules use ECExpressions?
    Does that mean you can use string.empty  as an empty string value in Item display rules?
    Or IsNullOrEmpty?

    tried to use the above, but didn't work for me, only the workaround did.
    CE update 14.

    Wouldn't ECExpression SymbolSet System.String need to be loaded to use string ECExpressions?


     think there should be a simpler list of what expressions if any that you can use in Display Rules.

  • CE update 14

    Expressions have advanced in recent versions of MicroStation CONNECT.  You'll find plenty by searching for Expressions in Update 16 help.

    If you're looking to create a display rule programmatically, then start with the C++ MicroStationAPI documentation.  For example...

    DisplayRuleSetPtr ruleSet = DisplayRuleSet::Create(L"RuleSetName", *dgnFile_);
    DisplayRulePtr MakeRule (WCharCP itemTypeName, WCharCP propName, WCharCP condition)
      WString prop (propName);
      WString rule;
      rule.Sprintf (L"element.%s::%s::%s%s",
        ItemTypes::SchemaInternalName ().c_str (),
        ItemTypes::GetInternalName (itemTypeName).c_str (),
      return MakeRule(rule.c_str ());
    DisplayRulePtr    MakeRule (WCharCP rule)
      const bool    StopIfTrue    {true};
      DisplayRulePtr  displayRule   {DisplayRule::Create(rule, StopIfTrue , *dgnFile_)};
      const bool    valid      {displayRule.IsValid ()};
      if (valid)
        // Created Display Rule:  rule
        // Display rule instruction rule is invalid
      return displayRule;

    Regards, Jon Summers
    LA Solutions

  • Hi Karsten,

    doesn't exist? 

    Well, when you re-open nearly a year old discussion, links can be invalid. I think it is not surprise.

    From the link it is visible it points to online documentation of some previous MicroStation version, which is not available now (I guess it was Update 14 or similar).

    Can you give the proper link

    I guess Jon answered this part already. To try to use Search in MicroStation documentation is where you should always start. It is really not difficult (15 seconds?) to find the same link in the current version: https://docs.bentley.com/LiveContent/web/MicroStation%20Help-v19/en/BetaExpressions.html

    or is this another link only available to Bentley employees?

    How can I know what links are available to Bentley employees?

    Display rules use ECExpressions?

    As documentation (DisplayRule Struct Reference) clearly tells: DisplayRule condition is based on ECExpressions.

    So, every rule is string, evaluated as ECExpression. The result is always true / false.

    Does that mean you can use string.empty  as an empty string value in Item display rules?

    In my opinion, not. And even when it would be possible, it is bad idea because of performance (do you know anything slower than string operations? ;-)

    As mentioned in documentation: Conditions should specify only stored values

    There is also written: Condition supports simple property value comparison as well as complicated conditions with AND and OR operators. No information about using Symbol Providers (libraries) to be able to extend standard comparisons.

    Following this rule, I think proper solution (somebody can say it is workaround) is to add extra bool property, containing ECExpression, defining whether source string property is null/empty. The result can be easily evaluated in Display Rule condition.

    think there should be a simpler list of what expressions if any that you can use in Display Rules.

    I think it is well enough (even when not ideally) described in API documentation: When you are not sure about syntax, use GUI to define condition and check how it is persisted.

    With regards,