Account Links Visibility¶

Currently we have four links associated with accounts (Register, Login, Account, Logout), but the relevance of these links depend on whether the user is logged in or not. If the user is logged in, they don’t need the login or register link, and, similarly, account and logout are not needed if the user is not logged in. So we should adjust the MainForm to not display irrelevant links. How will we do this?

Planning¶

Fortunately each layout element has a visibility property, so we can simply set this to True or False depending on the logged in status of the user.

In testing the last tutorial we used code the anvil.users.get_user() to show who the current logged in user was. If there was a user it returned <LiveObject>: anvil.table.Row, if there wasn’t a user it returned None. According to Python truthiness, any object is has a Boolean value or True, while None has a Boolean value of False.

Python Truthiness

In Python, “truthiness” refers to how values are evaluated in a boolean context, determining whether they are considered True or False. The values that return True are said to be Truthy, while the values that return False are called Falsy.

Truthy Values	Falsy Values
`not None`	`None`
Any non-zero number (e.g., 1, -1, 3.14)	Zero of any numeric type (eg. `0`)
Non-empty strings (e.g., “Hello”)	Empty string (eg. `""`)
Non-empty lists (e.g., [1, 2, 3])	Empty list (eg. `[]`)
Non-empty dictionaries (e.g., {“key”: “value”})	Empty dictionary (eg. `{}`)
Non-empty tuples (e.g., (1, 2))	Empty tuples (eg. `()`)
Non-empty sets (e.g., {1, 2, 3})	Empty set (eg. `set()`)
Objects by default	Special Objects that explicitly return `False`

We will use Python truthiness, get_user() and the links visibility to dynamically adjust the account links in respect to the users authentication.

We want to map it this way:

`get_user()`	Register visibility	Login visibility	Account visibility	Logout visibility
`True`	`False`	`False`	`True`	`True`
`False`	`True`	`True`	`False`	`False`

If you look at the table above you can see that the truthiness of:

Register visibility is the opposite of get_user()
Login visibility is the opposite of get_user()
Account visibility is the same as get_user()
Logout visibility is the same as get_user()

There the visiblity of the links can be rewritten as a function of the truthiness of get_user().

Register visibility = not get_user()
Login visibility = not get_user()
Account visibility = get_user()
Logout visibility = get_user()

Where should we place our code? It would be effective if the test is done each time the page changes. We just made a function set_active_link which we call each time a link is clicked, so we should put it there.

Code¶

Open the MainForm in code mode and go to the set_active_link method.

Then you want to enact our plan above by writing the highlighted code at the bottom of the set_active_link method.

  def set_active_link(self, state):
    if state == "home":
      self.link_home.role = "selected"
    else:
      self.link_home.role = None
    if state == "add":
      self.link_add.role = "selected"
    else:
      self.link_add.role = None
    if state == "calendar":
      self.link_calendar.role = "selected"
    else:
      self.link_calendar.role = None

    self.link_register.visible = not anvil.users.get_user()
    self.link_login.visible = not anvil.users.get_user()
    self.link_account.visible = anvil.users.get_user()
    self.link_logout.visible = anvil.users.get_user()

Code explaination

line 37:
- will set the visibility of link_register to opposite of the value returned by anvil.users.get_user()
- therefore if a user is logged in, link_register will not be visible, but if there is no user logged in, then link_register will be displayed.
line 38:
- will set the visibility of link_login to opposite of the value returned by anvil.users.get_user()
- therefore if a user is logged in, link_login will not be visible, but if there is no user logged in, then link_login will be displayed.
line 39:
- will set the visibility of link_account to the same value returned by anvil.users.get_user()
- therefore if a user is logged in, link_account will be displayed, but if there is no user logged in, then link_account will not be visible.
line 40:
- will set the visibility of link_logout to the same value returned by anvil.users.get_user()
- therefore if a user is logged in, link_logout will be displayed, but if there is no user logged in, then link_logout will not be visible.

Before we test our code, we have one more issue we need to resolve. We need to redirect the user to Home, after they have finished with Login, Register and Logout. To do this, add the following highlighted code.

  def link_register_click(self, **event_args):
    anvil.users.signup_with_form(allow_cancel=True)
    self.content_panel.clear()
    self.content_panel.add_component(HomeComponent())
    self.label_title.text = self.breadcrumb_stem
    self.set_active_link("home")

  def link_login_click(self, **event_args):
    anvil.users.login_with_form(allow_cancel=True)
    self.content_panel.clear()
    self.content_panel.add_component(HomeComponent())
    self.label_title.text = self.breadcrumb_stem
    self.set_active_link("home")

  def link_logout_click(self, **event_args):
    anvil.users.logout()
    self.content_panel.clear()
    self.content_panel.add_component(HomeComponent())
    self.label_title.text = self.breadcrumb_stem
    self.set_active_link("home")

Code explaination

These have been copied from the link_home_click method and are all the steps we need to do to load the HomeComponent.

Test¶

Before we test this code, go to the User table and delete all the rows (ie. all your users). Then launch your website.

Not Registered nor logged in¶

At first, since you now have no users, the user cannot possibly be logged in. You should see both the Register and the Login links.

test register

Registered and logged in¶

Click Register and register a new user (you can reuse the ones you deleted if you want).

Now there is a user logged in, so you only see the Account and Logout links.

test logged in

Logout¶

Now click the Logout button.

Since there is no user logged in you should see the Register and Login links.