---+ Package =TWiki::Form::FieldDefinition=

Base class of all field definition classes.

Type-specific classes are derived from this class to define specific
per-type behaviours. This class also provides default behaviours for when
a specific type cannot be loaded.


%TOC%

---++ ClassMethod *new* <tt>(%...)</tt>

Construct a new FieldDefinition. Parameters are passed in a hash. See
Form.pm for how it is called. Subclasses should pass @_ on to this class.



---++ ObjectMethod *finish* <tt>()</tt>
Break circular references.



---++ isEditable() -> $boolean

Is the field type editable? Labels aren't, for example. Subclasses may need
to redefine this.


---++ isMultiValued() -> $boolean

Is the field type multi-valued (i.e. does it store multiple values)?
Subclasses may need to redefine this.


---++ isTextMergeable() -> $boolean

Is this field type mergeable using a conventional text merge?


---++ isMandatory() -> $boolean

Is this field mandatory (required)?


---++ renderForEdit( $web, $topic, $value ) -> ($col0html, $col1html)
   =$web= - the web containing the topic being edited
   =$topic= - the topic being edited
Render the field for editing. Returns two chunks of HTML; the
=$col0html= is appended to the HTML for the first column in the
form table, and the =$col1html= is used as the content of the second column.


---++ getDefaultValue() -> $value
Try and get a sensible default value for the field from the
values stored in the form definition. The result should be
a value string.

Some subclasses may not support the definition of defaults in
the form definition. In that case this method should return =undef=.


---++ renderHidden($meta) -> $html
Render the form in =$meta= as a set of hidden fields.


---++ populateMetaDataFromQuery( $query, $meta, $old ) -> $boolean

Given a CGI =$query=, a =$meta= object, and an array of =$old= field entries,
then populate the $meta with a row for this field definition, taking the
content from the query if it's there, otherwise from $old or failing that,
from the default defined for the type. Refuses to update mandatory fields
that have an empty value.

Return true if the value in $meta was updated.


---++ ObjectMethod *renderForDisplay* <tt>($format,$attrs) -> $html</tt>

Render the field for display, under the control of $attrs.

The following vars in $format are expanded:
   $title - title of the form field
   $value - expanded to the *protected* value of the form field

The value is protected by TWiki::Render::protectFormFieldValue.


