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Building block for all CHT apps
Hiding Form Content
Controlling visibility of questions within a form
There are several different ways to control visibility of questions and other content within a form.
Conditionally hiding fields
Expressions in the relevant column can be used to dynamically control the visibility of questions, groups, etc. When the expression evaluates to true, the content is shown; when it evaluates to false, the content is hidden. This allows for showing/hiding content based on previous answers or other data in the form. The relevancy of a group is inherited by the fields it contains so, when a group is non-relevant, all of its contents will also be considered non-relevant.
When the form is completed, values for non-relevant fields will NOT be stored in the database.
Fields hidden by default
For a complete list of hidden fields, see ODKs site, otherwise see CHT relevant fields below.
calculate type
calculate fields are useful for storing data the user does not need to see but are referenced/used elsewhere in the form. The value contained in a calcuate field will be stored in the database when the form is completed.
The calcuate type is appropriate for fields with a defined initial value or whose value is calculated by the form logic. When a calculate field is definied in a form, it must have a value set in either the calculation or the default column.
hidden type
In some cases, a hidden field is needed, but there are no calculation or default value to set. In this case, the hidden type can be used. The value contained in a hidden field will be stored in the database when the form is completed.
When loading existing contact data into a form with the contact selector, hidden fields can be used to capture contact properties that should be stored when the form is saved, but not shown to the user.
hidden appearance
The CHT supports a custom hidden appearance on questions and groups that can be used to hide the associated UI elements when the form is rendered. This is useful for fields that should be included in the form’s data model and display template but should not be visible to the user when filling out the form. Values for fields with the hidden appearance will be stored in the database when the form is completed.
Several of the custom CHT form widgets need the associated field to exist in the form’s display template (and so cannot be used with the calculate or hidden types). In these cases you can use a standard question type (e.g. text) and an appearance value of hidden.
The hidden appearance can also be set on a group to hide all the contents of the group.
Setting the hidden appearance on a top-level group will prevent an extra blank page from being rendered for that group. However, due to performance optimizations in the Enekto library, for this to work, the form must include at least one relevant expression. (Otherwise, Enketo will automatically bypass all logic for hiding pages.) A relevant expression for any field in the form is enough. Alternatively, just set boolean(true) as the relevant value for the hidden group.
| type | name | appearance | relevant |
|---|---|---|---|
| begin_group | hidden_page | hidden | boolean(true) |
Note that just setting true/true()/etc as the appearance is not enough since Enketo will still bypass the relevancy logic.
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