Page Lifecycle

In FlutterFlow and Flutter, understanding the page lifecycle or simply the stages a page goes through from creation to disposal is essential for managing resources and data effectively.

Let's delve into the key moments in the lifecycle of a Page:

• Initialization: This is the first phase where the page is set up. Here the initial data is loaded. This might involve setting up the necessary state or defaults for the page.
• Rendering: Here, the page is actually drawn or rendered on the screen. This includes setting up the layout, styles, and any interactive elements. The user can now see the page in its initial state.
• Updating: After rendering, the page becomes interactive and can respond to user inputs such as clicks, typing, or other gestures. It may re-render parts of the page or the entire page to reflect the changes due to interaction or new data.
• Disposal: When the page is no longer needed, or the user navigates away, this phase is triggered. This is where resources related to the page are released from memory and are no longer accessible.

In FlutterFlow, most of these lifecycle phases are handled internally by FlutterFlow's architecture. However, we expose some of the methods so that you, as a developer, can decide what additional configurations to load upon initialization and when to re-render the UI based on interactions.

Let's read more about them in the following sections:

Initialization Action Triggers

During the initialization of a Page, we provide several Action Triggers that assist you in loading resources or initializing data. These triggers ensure that all necessary data is prepared and ready for use by the time the first frame of the Page is rendered.

What are Action Triggers?

Action Triggers serve as event listeners or handlers that respond to specific events or user interactions within an application. FlutterFlow provides developers with a way to define logic that responds to various events, such as button clicks, page loads, form submissions, or data changes. To learn more, head over to Action Flow Editor section.

As you open the Action Flow Editor for your Page, you can see the following Action Triggers exposed for your Page.

On Page Load [Action Trigger]

This allows you to set actions when the page loads or initializes. It enables developers to perform tasks or execute logic at specific points in the page lifecycle, such as fetching data from an API, initializing variables or updating UI elements.

Possible usecases

• Initializing Data: You can use the On Page Load action trigger to initiate API calls, database queries, or read from local storage, setting up the data that the page needs to display. This ensures that all necessary data is ready and available by the time the user sees the page.

• Setting State: If your page depends on certain state conditions (like toggles, selections, or input fields), you can set these states appropriately as the page loads.

• Running Animations: Start animations that welcome users or draw attention to certain UI elements on the page.

Adding an Action

To add an action to On Page Load action trigger, follow the steps:

On Phone Shake [Action Trigger]

Actions added under this trigger are triggered when the user shakes their phone. This is useful when you want to perform certain tasks or trigger specific actions in response to a phone shake gesture.

Possible usecases

• Randomizing content: Shake the phone to generate a random number, display a random quote, or change the background image.
• Refreshing data: Shake the phone to trigger a data refresh, such as fetching the latest news articles or updating a live feed.
• Resetting the app state: Shake the phone to reset the app state, clear form fields, or return to the app's home screen.

Page state

State Variables

A state variable holds information or data about your UI at any given moment. To learn more about states and state management, refer here

Page state refers to the information that a page tracks about its current condition or the data it displays. This can include things like which tabs are active, the contents of a form, or any user interactions. Managing state is crucial for dynamic pages that interact with user inputs or load varying data. Page State variables are only accessible within the given Page scope.

This type of variable can be useful for storing data that needs to be shared between different widgets on the page, such as saving form data, a search query, and filtering and sorting options.

For example,

• In a multistep form, you might use a Page State variable to store the current step number or the user's input for each step.
• Or, on a search results page, you could use a Page State variable to store the search query entered by the user and the current filtering and sorting options applied to the results.

This allows you to maintain the state of the page as the user interacts with different widgets and components.

When the value of a Page State variable is changed, you can choose to re-render the page with the updated values, and it will display a new version of the page with these updates.

Creating a Page State

To create a new Page State variable in your page, follow the steps:

While creating a Page State, the following properties are included:

• Is List: This property determines whether the variable can hold multiple values of the same data type (like a list or array) or just a single value.

• Initial Field Value: This property sets the default value for the variable when it is first created. It's like setting the starting point or the value that the variable begins with before anything else happens.

• Nullable: This property determines whether the variable can have a null value. When "Nullable" is set to true, it means the variable can be empty or have a null value. This is useful when dealing with optional data or scenarios where the absence of a value is valid.

Now, let's apply these concepts to the searchString variable in the context of the above example:

• Since searchString is used to store a single search query entered by the user in the search bar, "Is List" is set to false, therefore it can hold only one value at a time.

• The default value for searchString is set to an empty string (""). This ensures that when the homepage loads, the search bar is initially empty, allowing users to enter their search query.

• Since entering a search query is optional and the search bar can be left empty, "Nullable" is set to true. This allows the searchString variable to be null until the user enters a search query, indicating that no search has been performed yet.

note

You can set the Data Type of your Page State variable to any primitive data types such as String, Integer, Boolean, Double or to any other complex built-in data types such as Enum, Custom Data Type, Document, etc. To learn more about the available data types, refer the Data Representation Section.

Get Page State value

You can access the Page State value anywhere on the current page. Any widget can hold the current value of a given Page State variable, either for directly displaying it in the UI or for transactional logic.

You can set the source value of the widget wherever you see the following icon. This icon indicates that you can link the widget’s value to a variable.

Update Page State [Action]

Page State values can only be updated via Actions. Whenever you want to update the page state, such as through a button click, user interaction, or form update, create a new Action called Update Page State.

Rebuild on Update

When updating your page state in Flutter, you'll often come across the Update Type property in your Action properties. Here's what it means:

Rebuild Current Type: This option triggers a re-rendering of the page, ensuring that any changes to the state are reflected in the user interface (UI).

No Rebuild: Choose this option when you need to update the state without immediately reflecting the changes in the UI.

Expensive Rebuilds

Too many rebuilds can impact performance because rebuilding the widget tree frequently consumes resources and may lead to decreased responsiveness and increased battery usage. Therefore, it's essential to consider the trade-offs and use rebuilds judiciously to maintain optimal app performance.

To learn more about what happens behind the scenes, refer to the [Generated Page] section.