S3Navigation

S3Navigation is an S3 module providing a generic framework for the implementation of navigation elements in the web UI.

S3NavigationItem

S3NavigationItem is a base class for the implementation of navigation items, and provides the common logic for all types of navigation items as well as an API for renderers.

Navigation items are UI elements to navigate the application, and can appear as menus, breadcrumb rows, tab rows, and various other types of links. They all have in common that they are linked to request URLs and usually get activated by clicking them.

Subclassing S3NavigationItem

The S3NavigationItem class is not meant to be used directly for the implementation of navigation items. Instead, it should be subclassed for each type of navigation items the user interface needs. Subclasses of S3NavigationItem are supposed to implement the layout of the respective item type, and are therefore referred to as Layouts.

To implement a Layout, create a new subclass of S3NavigationItem and implement a (static) method layout:

class MyMenuLayout(S3NavigationItem):

    @staticmethod
    def layout(item):
        # Layout implementation goes here

The layout method takes an instance of the layout class as parameter, and returns an instance of a web2py HTML helper class (DIV or a subclass of it). This HTML instance is what eventually gets written into the view.

The layout method can make use of the renderer API to retrieve the item's attributes and flags.

Defining Navigation Items

Once you have implemented the Layout, you can create instances of it to define the particular navigation elements. The elements can be nested using the call-method:

my_menu = MyMenuLayout("Home")(
             MyMenuLayout("First Item"),
             MyMenuLayout("Second Item"),
             MyMenuLayout("Submenu")(
                 MyMenuLayout("First SubmenuItem"),
                 MyMenuLayout("Second SubmenuItem")
             )
           )

Each navigation item can receive any number of keyword parameters.

The following keyword parameters are used by the base-class:

Keyword	Type	Meaning	Comments
label	string	The label for the item (if any)	always the first parameter, so the keyword can be omitted; labels which are not already T instances (localized strings) will automatically be rendered with T unless you set translate=False
r	Request	The request object	if passed, then the item inherits a, c, and f from this request, i.e. the item will always match this request
a	string	The application name in the target URL	inherited from parent item
c	string	The controller name in the target URL	inherited from parent item
f	string	The function name in the target URL	inherited from parent item
args	list of strings, or string	the arguments in the target URL	if passed as single string, the arguments must be separated by slashes
vars	dict of strings	the query variables in the target URL
extension	string	the URL extension (data format extension) in the target URL	defaults to None
p	string	the permission required to access this item	defaults to m
m	string	the URL method for the request	defaults to "", will be appended to args if not the last arg
t	string	the name of the table the permission is required for	defaults to <c>_<f>
tags	list of strings	a list of tags for this item	tags can later be used to address this item in the menu tree, e.g. to update flags
parent	the parent item	set the parent item explicitly	special purpose, defaults to None and should be left at that
translate	boolean	False will prevent automatic localization of the item label
layout	function	use this function to render this item instead of the layout of the class
check	boolean, function or mixed list of these types	conditions to check before rendering	functions will be called with the item as parameter and are expected to return a boolean
restrict	list of role IDs or UIDs	restrict access to this item to these roles
link	boolean	whether to link this item to the specified target URL or not	defaults to True = all items get linked
mandatory	boolean	override active check - item is always active	not implemented yet

All other keyword parameters will be stored in the item instance as they are and get passed on to the layout method. Keywords starting with an "_" underscore will be stored in the item.attr dict, all other keywords in the item.opts dict. It is up to the layout method to deal with those keyword parameters then.

Status Flags

During the status check cascade, each navigation item receives a set of status flags which then are available to the layout method. It is up to the layout method whether and how each combination of flags influences the rendering of the item.

Flag	Meaning	Comments
item.enabled	The item shall be rendered as enabled (accessible)	renderers would usually skip items with enabled=False, but could also render them greyed-out or otherwise visible but inaccessible; this flag will be altered by the return value of the check-hooks, and can be overridden by the check_enabled method of the class
item.selected	The target URL of the item or any of its sub-items matches the current request	this can be used for menu highlighting; if more than one subtree can be matched, only items in the first matching subtree will be marked selected
item.authorized	The user is permitted to access the target URL of this item	renderers would usually skip items the user is not permitted to access, but could also render the item greyed-out or otherwise visible but inaccessible
item.visible	Custom flag to show/hide items	will always be True unless explicitly changed by a check-hook method

Status Check Cascade

All S3Navigation items are run through a cascade of status checks before they get handed over to the layout method.

The default behavior of these methods is meant for menu items, which may though not fit for all types of navigation items. Where needed, the subclass should overwrite them accordingly. These methods won't take any parameter beyond self and are expected to return a boolean value. The methods are called in the order they appear in the following table:

Method	Meaning	Effect	Flag set	Standard Behavior
check_active	Check whether the item is relevant for the current request	if this returns False, the item will be deactivated and no further checks nor the renderer ever be invoked (abort)		check_active returns False if a target controller is defined, but disabled in deployment settings, or if neither the item nor any of the items in the same subtree anyhow matches the request
check_permission	Check whether the user is permitted to access the target URL of the item	sets flag	authorized	returns True if an auth.accessible_url can be created from the target URL
check_selected	Check whether the item matches the current request	sets flag upward in the whole subtree	selected	returns True if this item or any of its children, out of all items in the tree, reaches the highest match-level for the current request
check_hook	Runs the check-hook methods defined for this item	if this returns False, neither check_enabled nor the renderer will be run		returns True only if all check-hooks return True, otherwise False
check_enabled	Check whether the item is enabled	Overrides the enabled flag if (and only if) it returns False, if it returns True, the flag remains unchanged	enabled	by default, check_enabled returns always True

Implementing Layouts

Subclasses of S3NavigationItem must implement the layout method:

class MyMenuLayout(S3NavigationItem):

    @staticmethod
    def layout(item):
        # Layout goes here

Usually, this should be a static method. It will be called with an instance of the same class, and is expected to return a web2py HTML helper instance (i.e. a subclass of DIV, which implements the xml method).

S3NavigationItem provides an API for the layout method (=renderer) to introspect the item before rendering.

Item Attributes

Attribute	Type	Contents	Comments
label	T instance or str	the localized label for this item	can be None for container items
controller	string	controller name of the target URL	don't use directly, use get method instead
function	string	function name of the target URL	don't use directly, use get method instead
application	string	application name of the target URL	don't use directly, use get method instead
r	request object	the request this item was matched against	defaults to current.request
args	list of strings	the args for the target URL
vars	dict of strings	the query variables for the target URL
extension	string	the format extension for the target URL
tablename	string	the name of the target table of the target URL
attr	dict	the HTML attributes	as passed during item definition
opts	dict	the renderer options	as passed during item definition
authorized	Flag	whether the current user is permitted to access the target URL
enabled	Flag	whether the item is enabled
visible	Flag	whether the item shall be visible	renderers should always respect this flag
selected	Flag	whether the item belongs to the currently selected menu path
parent	navigation item	the parent item	None if this is a top-level item
components	list of navigation items	all sub-items for this item	empty list if this is a leaf item

Introspection Methods

S3NavigationItem provides a number of helper methods for item introspection:

Get a sub-item of this item:

    sub_item = item[i]

Loop over sub-items:

    for sub_item in item:
        ...

Get the root item of the tree:

    root_item = item.get_root()

Get the path (list of items) from the root item down to this item:

    path = item.path()

Get all sub-items with certain flags (can also take multiple flags):

    enabled_sub_items = item.get_all(enabled=True)

Get the first sub-item with certain flags (can also take multiple flags):

    first_authorized_and_enabled_sub_item = item.get_first(enabled=True, authorized=True)

Get the last sub-item with certain flags (analogous to above):

    last_authorized_and_enabled_sub_item = item.get_last(enabled=True, authorized=True)

Number of sub-items:

    number_of_subitems = len(item)

Position of a sub-item within the sub-items list:

    sub_item_position = item.index(sub_item)

Check whether this is the first sub-item with certain flags:

    is_first_enabled = item.is_first(enabled=True)

Check whether this is the last sub-item with certain flags:

    is_last_authorized_and_visible = item.is_last(authorized=True, visible=True)

Get all preceding siblings of this item within the parent (as list):

    preceding_siblings = item.preceding()

Get all following siblings of this item within the parent (as list):

    following_siblings = item.following()

Get the last preceding item with certain flags:

    preceding_enabled = item.get_prev(enabled=True)

Get the first following item with certain flags:

    following_visible_and_enabled = item.get_next(visible=True, enabled=True)

Get the item URL:

    url = item.url()

Get an inherited attribute (i.e. controller, function or application; these attributes should never be accessed directly):

    controller = item.get("controller")

Check whether this item or any item underneath it contains a certain tag:

    tag = "special"
    if tag in item:
        # This item or at least one underneath it contains this tag

Manipulation methods

These methods can be used by controllers to influence the rendering of items:

Get all items underneath this item with a certain tag (as list):

    tag = "special"
    special_items = item.findall(tag)

Enable/disable items by tag:

    tag = "special"
    item.enable(tag) # enables all descendand items with the tag "special"

    tag = "nonspecial"
    item.disable(tag) # disables all descendand items with the tag "nonspecial"

If enable or disable are used without tag, then only the current item gets enabled/disabled

Set layout:

    tag = "special"
    def f(item):
        # Layout goes here

    # Set this layout to all descendand items with the tag "special"
    item.set_layout(f, tag=tag, recursive=True)

Rendering Methods

Invoking the Renderer

To render a navigation element (i.e. to run the layout method), just put it into the view like:

{{=my_menu}}

This will call the layout method of the element, provided that the element is active (i.e. relevant for the current request).

Eden Standard Menus

Customizing Menus