Show 'N Tell Thursday: Writing better hide-when formulas

Thu 23 Mar 2006, 11:29 AM

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by Ben Langhinrichs

1. Hide-when formulas effect entire paragraphs (a table cell starts with a paragraph, so this is true in table cells as well, although a table cell may have multiple paragraphs.  See more on paragraphs).
2. A hide-when formula should always either be a condition (e.g., Status = "Pending") or return a @Yes or @No (or @True or @False, which are equivalent).
3. Multiple conditions should be combined with an ampersand, &, if all the conditions must be true in order to hide the paragraph, or with a vertical bar, |, if any one of the conditions must be true to hide the paragraph.  For example, if we should hide the paragraph when either Status is "Pending" or Override is "Denied", the formula should be Status = "Pending" | Override = "Denied".
4. If you have mixed conditions, use parentheses to separate the "and" and "or" parts.  For example, if the paragraph should be hidden when either Status is "Pending" or Override is "Denied, but not when the document is being edited, the formula should be (Status = "Pending" | Override = "Denied") & !@IsDocBeingEdited.

1. Do not use an @If unless you really, really need to.  The formula @If(Status = "Pending"; @True; @False) should be simplified to Status = "Pending".
2. Formula language allows you to check against a list of names at one time, so the formula Status = "Pending" | Status = "Denied" | Status = "Reviewed" should be simplified to Status = "Pending":"Denied":"Reviewed", with the colon between the items being a list separator.
3. If it is very hard to describe the "hide when" condition, but easy to describe the "show when" condition, just put the "show when" condition in parentheses and use an exclamation mark, which means "not" in front.  Thus, if the paragraph should be shown (not hidden) when the Type is 1 or the document is being edited, you can use !(Type=1|@IsDocBeingEdited) instead of trying to figure out the inverse.
4. Beware of mixed conditions.  If you have a formula which says Status = "Denied" | Type = 3 & @IsDocBeingEdited, how do you know whether the proper meaning is (Status = "Denied" | Type = 3) & @IsDocBeingEdited or Status = "Denied" | (Type = 3 & @IsDocBeingEdited), which have very different meanings.  If you assume the first interpretation, your paragraph may be hidden whenever you are in edit mode, but if you assume the second, it will only be hidden in edit mode when the Type is 3.
5. Try "talking the formula".  If you have a formula which says Status = "Denied" | Type = 3, and you try to say it out loud as "Hide this paragraph if Status is "Denied" or Type is 3", you may catch that what you wanted was "Hide this paragraph if Status is "Denied" and Type is 3", which should be Status = "Denied" & Type = 3.

1. Include a "back door".  A hide-when formula on a form includes an implicit assumption that you can always see the hidden paragraph when designing the form.  There is no such assumption with rich text fields.  If your formula would have been Donations = 0.0, make it Donations = 0.0 & (!@IsDocBeingEdited).  Then, you can still see the paragraph when editing.  Another option is to check a special role, so that when that role is set, you can see all hidden paragraphs.  If you don't do this, you may find hidden paragraphs that you can't ever find again.
2. Be clear you are using hide-when formulas with users (or admin or somebody).  People don't expect hide-when formulas, and won't be very happy if they feel "fooled".

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