Building reusable UIs with Layouts

When you create a multi-page app, there will be parts of the UI that will be shared across multiple Forms - for example, a navigation bar. Layouts let you create user interfaces that multiple Forms can use. I'm going to show you how to create one.

In this tutorial, we'll build a homepage Layout with a navigation sidebar, and we'll use it as the Layout for the other Forms in our app. When a user clicks a link in the sidebar, the app will open a new Form that has different content but the same navigation menu.

What are Layouts?

In Anvil, a Layout is a Form that can be used by other Forms to define their structure. A Layout Form can have components added to it. Any Form using the same Layout will all have those same components. When you create a Layout Form, you add Slots into the design. Slots define where Forms using the Layout can add components.

Tutorial Prerequisites

To follow along this tutorial you will need to know basic Python and you should know the basics of Anvil. If you're new to Anvil, why not try our introductory Feedback Form tutorial?

Contents

These are the steps that we will cover:

• Step 1 - Create an Anvil app
• Step 2 - Create a homepage Layout
• Step 3 - Create a navigation menu
• Step 4 - Add a slot
• Step 5 - Use the Layout
• Step 6 - Wire up the navigation menu
• Step 7 - Make the link look selected
• Step 8 - Test the app
• Step 9 - Optional: Change the homepage Layout

Step 1 - Create your Anvil app

Log in to Anvil and click 'Blank App'.

When you're asked what you'd like your page to look like, select Material Design 3:

Click on the name at the top of the screen and give your app a name.

Step 2 - Create your homepage template

Our app already has a Form added called Form1, which we'll turn into our homepage Layout. Open Form1 and change the name to "Homepage":

Then, click the three dot icon above the form and select "Use as layout":

The first time you use Layouts in your app, you’ll need to migrate the app to use the new UI features. If the app hasn’t yet been migrated, you’ll see a popup message when you change your Form to a Layout. This is an irreversible change to our app, so please be aware if you’re migrating an app you’ve built with the old Anvil Designer.

Let's add a description of our Layout in the form's configuration menu. This information shows up when deciding which template a new form should use. Click the three dot icon above the form again and select "Edit properties and events". Then add a description.

That's great. Next up, let's build a navigation UI in our ayout for other forms to inherit.

Step 3 - Creating our navigation menu UI

Let's start by adding a Column Panel into the sidebar of our Form.

Then we can drag two Link components into the Column Panel - one for each Form that will use this Layout. We'll change the first link's text to "About Us" and the second link's text to "Contact Us".

Lastly, let's give our app a title by dragging a Label into the title section on the top left of the Homepage Form. Then change the Label's role to Title.

Step 4 - Adding a slot

Now that we've built the Layout we want our other Forms to use, let's add a Slot. Slots define where components can be inserted by Forms that use the Layout.

We’ll add a Slot to the content_panel of our Homepage by dragging in a “Slot” from Toolbox on to the right of the designer.

Each Slot has a name. We can rename our slot using the object palette. Let's call it main_slot.

Be aware that if you delete or rename a Slot from a Layout that is being used by another Form, any components that were inside that Slot will not know where to go. You can find them in the Orphaned Components Panel and add them back to your page. For more information, see our documentation on Layouts

Great, our Layout's UI is complete. Now it's time to create some Forms that use our Layout.

Step 5 - Using the Layout

We're now going to create two Forms called "AboutUs" and "ContactUs" that use our Layout Form. Later, we'll add click event functions to the Links we added in the previous step so that they open the corresponding Form when clicked.

First, we'll create AboutUs by clicking "Add Form" in the App Browser.

Then, select the Homepage.

We can then rename the Form to "AboutUs", the same way we renamed the Homepage Form.

Then, let's add a label to the main slot and change its text.

Repeat this process for the ContactUs page, adding another label with some different text.

Now that we have two Forms using our Layout, all we have to do is wire up the sidebar links so they open the corresponding Form when clicked.

Step 6 - Wiring up the navigation menu

Open the Homepage Form and select the "About Us" link in the navigation menu. Let's first rename the Link so that it's easier to reference in code. In the floating Object Palette, click on link_1 and rename the Link to about_us_link. Next, select on click event, this will open up the code view for our Form and create an event handler function for us.

Inside the event function, we'll use the open_form function to open our AboutUs page by passing in the name of the Form as a string.

def about_us_link_click(self, **event_args):
  """This method is called when the link is clicked"""
  open_form('AboutUs')

Now, every time the "About Us" link is clicked, it will load the corresponding page. We will also do the same for the "Contact Us" link by renaming the link, adding the click event and opening the relevant Form in the function.

Lastly, let's create a reset_links function for the Forms using our template to use. Create the function and inside, set every Link component's role to a blank string:

def reset_links(self, **event_args):
  self.contact_us_link.role = ''
  self.about_us_link.role = ''

Step 7 - Making the Link look selected

Our final step is to make it so that when we click one of the links in our navigation menu, it looks selected. This will make it easier to tell what page we are already on.

Select the AboutUs Form in the designer and in the Events section of the properties panel, click the blue button next to the "Show" event.

This will open up the code view and add a function that will run every time the AboutUs Form is shown.

Inside the function, we can interact with the Layout our Form is using with self.layout. This gives us the ability to call functions defined in our Layout and change the properties of the Layout's components. Let's reset the links and set the role of the Homepage.about_us_link to be "selected".

def form_show(self, **event_args):
    """This method is called when the form is shown on the screen"""
    self.layout.reset_links()
    self.layout.about_us_link.role = 'selected'

Repeat this process for ContactUs.

Step 8 - Testing the app

To see the app in action, click the "Run" button at the top of the screen:

Click each link in the sidebar, and the relevant page should appear using our Layout.

Step 9 - Optional: Changing the Homepage Layout

This part is optional! The best way to learn any new technology is to challenge your understanding. Why not challenge yourself to reinforce what you’ve learnt and learn more?

One of the best things about Layouts is making a change to the Layout is instantly propagated to all forms using the Layout. So, why not make some changes to our homepage form and see how it affects the other forms. You could:

• Add another link to the navigation sidebar and wire it up
• Add a slot to the sidebar in Homepage so that other Forms using the Layout can add more links to the navigation menu
• Chain Layouts together. Try creating an "Admin" page which uses the Homepage Layout and, in turn, make that a Layout. The admin page could have its own naigation menu inside the homepage's main slot with links for "Profile" and "Contact Preferences".

Clone the App

You can open the source code for the finished Anvil app here.

More about Anvil

If you're new here, welcome! Anvil is a platform for building full-stack web apps with nothing but Python. No need to wrestle with JS, HTML, CSS, Python, SQL and all their frameworks – just build it all in Python.

RyanFollow

Software developer. Tech enthusiast. Follow me for Python, Anvil and software development content.