5.6.3 Form data

Procedure: data-ahead? form

Procedure: data-behind? form

These procedures test if there is ahead or behind the current screen of the given form form. They return #t or #f.

This could be because a text entry has been declared to have variable size (not O_STATIC) and not all text from the entry is being displayed.

5.6.4 Command-processing loop of the form system

Constant: %is-form-driver-wide

This constant is #t if the form-driver function is capable of processing characters with representations that are greater than 8 bits.

Procedure: form-driver form c

Once a form has been posted (displayed), you should funnel input events to it through form-driver. This routine has three major input cases:

• The input is a form navigation request. Navigation request codes are constants defined below, which are distinct from the key and character codes returned by wgetch.
• The input is a printable character.
• The input is the KEY_MOUSE special key associated with an mouse event.

The form driver requests are as follows:

Name	Description
REQ_NEXT_PAGE	Move to the next page.
REQ_PREV_PAGE	Move to the previous page.
REQ_FIRST_PAGE	Move to the first page.
REQ_LAST_PAGE	Move to the last field.
REQ_NEXT_FIELD	Move to the next field.
REQ_PREV_FIELD	Move to the previous field.
REQ_FIRST_FIELD	Move to the first field.
REQ_LAST_FIELD	Move to the last field.
REQ_SNEXT_FIELD	Move to the sorted next field.
REQ_SPREV_FIELD	Move to the sorted previous field.
REQ_SFIRST_FIELD	Move to the sorted first field.
REQ_SLAST_FIELD	Move to the sorted last field.
REQ_LEFT_FIELD	Move left to a field.
REQ_RIGHT_FIELD	Move right to a field.
REQ_UP_FIELD	Move up to a field.
REQ_DOWN_FIELD	Move down to a field.
REQ_NEXT_CHAR	Move to the next char.
REQ_PREV_CHAR	Move to the previous char.
REQ_NEXT_LINE	Move to the next line.
REQ_PREV_LINE	Move to the previous line.
REQ_NEXT_WORD	Move to the next word.
REQ_PREV_WORD	Move to the previous word.
REQ_BEG_FIELD	Move to the beginning of the field.
REQ_END_FIELD	Move to the end of the field.
REQ_BEG_LINE	Move to the beginning of the line.
REQ_END_LINE	Move to the end of the line.
REQ_LEFT_CHAR	Move left in the field.
REQ_RIGHT_CHAR	Move right in the field.
REQ_UP_CHAR	Move up in the field.
REQ_DOWN_CHAR	Move down in the field.
REQ_NEW_LINE	Insert or overlay a newline.
REQ_INS_CHAR	Insert a blank at the cursor.
REQ_INS_LINE	Insert a blank line at the cursor.
REQ_DEL_CHAR	Delete character at the cursor.
REQ_DEL_PREV	Delete character before the cursor.
REQ_DEL_LINE	Delete line at the cursor.
REQ_DEL_WORD	Delete blank-delimited word at the cursor.
REQ_CLR_EOL	Clear to end of line from cursor.
REQ_CLR_EOF	Clear to end of field from cursor.
REQ_CLR_FIELD	Clear the entire field.
REQ_OVL_MODE	Enter overlay mode.
REQ_INS_MODE	Enter insert mode.
REQ_SCR_FLINE	Scroll the field forward a line.
REQ_SCR_BLINE	Scroll the field backward a line.
REQ_SCR_FPAGE	Scroll the field forward a page.
REQ_SCR_BPAGE	Scroll the field backward a page.
REQ_SCR_FHPAGE	Scroll the field forward half a page.
REQ_SCR_BHPAGE	Scroll the field backward half a page.
REQ_SCR_FCHAR	Scroll the field forward a character.
REQ_SCR_BCHAR	Scroll the field backward a character.
REQ_SCR_HFLINE	Horizontal scroll the field forward a line.
REQ_SCR_HBLINE	Horizontal scroll the field backward a line.
REQ_SCR_HFHALF	Horizontal scroll the field forward half a line.
REQ_SCR_HBHALF	Horizontal scroll the field backward half a line.
REQ_VALIDATION	Validate field.
REQ_NEXT_CHOICE	Display next field choice.
REQ_PREV_CHOICE	Display previous field choice.

If the second argument is a printable character, the driver places it in the current position in the current field. If it is one of the forms requests listed above, that request is executed.

It is important to note that when characters are Unicode codepoints greater than U+00FF, the form driver will only use them for versions of the wide ncurses form library that are 2014 or newer. For older version of ncurses, only printable characters (which must be positive, less than 256) are allowed. The %is-form-driver-wide constant can be used to check if form-driver can handle characters whose numerical representations are greater than 256.

If the second argument is the KEY_MOUSE special key, the associated mouse event is translated into one of the above pre-defined requests. Currently only clicks in the user window (e.g. inside the form display area or the decoration window) are handled.

If you click above the display region of the form:

• a REQ_PREV_FIELD is generated for a single click,
• a REQ_PREV_PAGE is generated for a double-click and
• a REQ_FIRST_FIELD is generated for a triple-click.

If you click below the display region of the form:

• a REQ_NEXT_FIELD is generated for a single click,
• a REQ_NEXT_PAGE is generated for a double-click and
• a REQ_LAST_FIELD is generated for a triple-click.

If you click at an field inside the display area of the form:

• the form cursor is positioned to that field.
• If you double-click a field, the form cursor is positioned to that field and E_UNKNOWN_COMMAND is returned. This return value makes sense, because a double click usually means that an field-specific action should be returned. It is exactly the purpose of this return value to signal that an application specific command should be executed.
• If a translation into a request was done, form_driver returns the result of this request.

If you clicked outside the user window or the mouse event could not be translated into a form request an E_REQUEST_DENIED is returned.

If the second argument is neither printable nor one of the above predefined form requests, the driver assumes it is an application-specific command and returns E_UNKNOWN_COMMAND. Application-defined commands should be defined relative to MAX_COMMAND, the maximum value of these pre-defined requests.

form-driver returns one of the following error codes: E_OK if the routine succeeded, E_BAD_ARGUMENT if the routine detected an incorrect or out-of-range argument, E_BAD_STATE if the routine was called from an initialization or termination function, E_NOT_POSTED if the form has not been posted, E_INVALID_FIELD if the contents of field is invalid, E_REQUEST_DENIED if the form driver could not process the request, E_SYSTEM_ERROR if a system error occurred, and E_UNKNOWN_COMMAND if the form driver code saw an unknown request code.