Project: Building a Simple Task List Manager

Introduction

Welcome back! In our previous chapters, we laid the groundwork for understanding GPUI’s core components: the Application, Window, and fundamental View concepts. Now, it’s time to put that knowledge into action by building a practical application.

This chapter guides you through creating a simple, yet fully functional, Task List Manager. This project is an excellent next step because it combines several crucial GPUI concepts:

• Managing application state: How to store and update a collection of items (our tasks).
• Rendering dynamic lists: Displaying multiple UI elements based on data.
• Handling user input: Capturing text for new tasks.
• Responding to actions: Marking tasks as complete or deleting them.

By the end of this chapter, you’ll have a working task manager and a much deeper understanding of how to build interactive, stateful applications with GPUI. Get ready to write some Rust and see your UI come to life!

Core Concepts for Our Task List

Before we dive into the code, let’s outline the core concepts and components we’ll need for our task list manager. Think of these as the building blocks of our application.

The Task Data Structure

Every task in our list needs to hold some information. At a minimum, we’ll need:

• A description of the task (e.g., “Buy groceries”).
• A status indicating if it’s completed or not.

We’ll represent this with a simple Rust struct. This allows us to group related data together into a single, cohesive unit.

Central Application State

Our task list needs to live somewhere. In GPUI, application-specific state often resides within an Entity that implements the View trait. For our task manager, we’ll create a main view that holds a collection of Task objects. This central view will be responsible for:

• Adding new tasks to its collection.
• Updating existing tasks (e.g., marking as complete).
• Removing tasks from the list.
• Notifying GPUI when its internal state changes, which in turn prompts the UI to re-render.

Displaying Dynamic Lists

Unlike static “Hello World” examples, a task list changes as users add, complete, or delete tasks. We need a way to:

1. Iterate over our collection of Tasks held in the view’s state.
2. For each Task, create a corresponding UI element (like a row containing a checkbox and the task’s text).
3. Ensure these UI elements update automatically when the underlying Task data changes (e.g., when a task is marked complete).

GPUI’s elements API and reactive rendering model are perfect for this. We’ll use layout primitives like div to arrange our individual task items vertically within the main view.

User Input and Actions

To make our task list interactive, we’ll need:

• An input field (text_input) for users to type in new tasks.
• A mechanism to submit that input (e.g., pressing the Enter key).
• A way to trigger specific actions, such as toggling a task’s completion status (e.g., clicking a checkbox) or deleting a task (e.g., clicking a button).

GPUI uses an Action system, allowing us to define specific events (like Add or Delete) and bind them to UI interactions. For per-item interactions, we’ll also see how direct event handlers like on_mouse_down can be used.

The Hybrid Rendering Model Revisited

As we build this, remember GPUI’s core differentiator: its hybrid immediate and retained mode rendering, accelerated by the GPU. When you modify the state of your view and call cx.notify(), you’re essentially telling GPUI, “Hey, something changed in my data; please re-evaluate my render() method.” GPUI then efficiently re-draws only the parts of the UI that need updating on the GPU. This is why explicitly triggering re-renders when state changes is crucial for a responsive user experience.

Step-by-Step Implementation

Let’s start building! We’ll begin with the basic structure and incrementally add features.

1. Project Setup

First, ensure you have a new Rust project and GPUI added as a dependency. If you haven’t already, create a new project:

cargo new gpui_task_list --bin
cd gpui_task_list

Now, open your Cargo.toml and add GPUI. As of 2026-05-24, GPUI is still under active development, and the most up-to-date source is often directly from the Zed repository’s main branch. For this tutorial, we’ll reference it directly from GitHub.

# Cargo.toml
[package]
name = "gpui_task_list"
version = "0.1.0"
edition = "2021"

[dependencies]
gpui = { git = "https://github.com/zed-industries/zed", branch = "main" }

🧠 Important: Using git = "..." and branch = "main" means you’re tracking the development branch. This is common for GPUI due to its rapid evolution but also means APIs can change frequently. Always be prepared to consult the Zed gpui crate README and the Zed editor’s source code for the latest patterns.

2. Defining the Task Model

Let’s create our Task struct. Open src/main.rs and add this at the top.

// src/main.rs

use gpui::*; // Import all necessary GPUI items

// Define a global action for adding tasks.
// Per-item actions like deletion will be handled with direct event handlers.
gpui::actions!(tasks, [Add]);

#[derive(Debug, Clone, PartialEq)] // Derive common traits for convenience
struct Task {
    id: usize,
    description: String,
    completed: bool,
}

impl Task {
    fn new(id: usize, description: String) -> Self {
        Self {
            id,
            description,
            completed: false,
        }
    }
}

Explanation:

• use gpui::*;: This brings all necessary GPUI types and macros into scope.
• gpui::actions!(tasks, [Add]);: We define a global Add action within the tasks module. This action can be triggered from anywhere in the application and will be handled by our TasksView.
• #[derive(Debug, Clone, PartialEq)]: These derive macros automatically implement common traits. Debug helps with printing, Clone allows us to easily duplicate Task instances, and PartialEq enables comparison, which is useful for tasks.
• id: usize: A unique identifier for each task. This will be important for updating or deleting specific tasks from our list.
• description: String: The actual text content of the task.
• completed: bool: A flag to indicate if the task has been completed.
• fn new(...): A simple constructor (associated function) to create new Task instances with an initial ID and description, defaulting to completed: false.

3. Setting Up the Main Application View

Now, let’s create our main application view, TasksView, which will hold and manage our list of tasks. This view will also be responsible for handling interactions.

// src/main.rs (continued)

// ... (Task struct and impl from above)

struct TasksView {
    tasks: Vec<Task>,
    next_task_id: usize,
    new_task_input: String, // State for the text input field
}

impl Entity for TasksView {
    type Event = (); // For now, we don't define custom events that bubble up from TasksView
}

impl TasksView {
    // Method to handle adding a new task, triggered by the `tasks::Add` action.
    fn handle_add_task(&mut self, _action: &tasks::Add, cx: &mut ViewContext<Self>) {
        // 🧠 Important: This method modifies the view's state (`self`).
        // It's called within a context that allows safe mutation.
        if !self.new_task_input.is_empty() {
            let new_task = Task::new(self.next_task_id, self.new_task_input.clone());
            self.tasks.push(new_task);
            self.next_task_id += 1;
            self.new_task_input.clear(); // Clear the input field after adding
            cx.notify(); // Tell GPUI that the view's state has changed and it needs to re-render.
        }
    }
}

impl View for TasksView {
    fn ui_name() -> &'static str {
        "TasksView"
    }

    fn render(&mut self, _cx: &mut ViewContext<Self>) -> AnyElement {
        // We'll fill this in next! For now, a simple placeholder.
        div().child(text("Loading tasks..."))
            .into_any_element()
    }
}

Explanation:

• struct TasksView: This defines the structure of our main view, which contains:
  • tasks: Vec<Task>: The vector holding all our Task objects. This is the core state.
  • next_task_id: usize: A simple counter to assign unique IDs to new tasks.
  • new_task_input: String: Stores the current text entered by the user in the “Add new task” input field.
• impl Entity for TasksView: This trait implementation marks TasksView as an entity that can be managed by GPUI’s context system. type Event = (); indicates it doesn’t emit custom events to its parent for now.
• impl TasksView { fn handle_add_task(...) }: This is a regular method on our TasksView struct. It’s designed to be called when the tasks::Add action is triggered. It performs the logic of creating a new task, adding it to the tasks vector, clearing the input, and most importantly, calling cx.notify() to signal a UI update.
• impl View for TasksView: This is the crucial part that tells GPUI how to render our view.
  • fn ui_name(): Provides a debug name for the view, useful for introspection.
  • fn render(): This method describes what our UI looks like based on the current state (self). For now, it’s just a placeholder element.

4. Initializing the TasksView and Application

We need to create an instance of TasksView and launch our GPUI application, placing our view within a window.

// src/main.rs (continued)

// ... (Task struct and impl, TasksView struct and impl, TasksView::handle_add_task impl)

fn main() {
    App::new().run(|cx: &mut AppContext| {
        // Create an initial TasksView.
        // `cx.new_view` takes a closure that returns our view instance.
        let tasks_view = cx.new_view(|cx| TasksView {
            tasks: vec![
                Task::new(0, "Learn GPUI basics".to_string()),
                Task::new(1, "Build a task list".to_string()),
            ],
            next_task_id: 2,
            new_task_input: String::new(),
        });

        // Open a new window and display our TasksView as its root content.
        cx.open_window(WindowOptions::default(), |cx| {
            // The root view of the window is our TasksView.
            // `into_any_view` converts our typed ViewHandle into a generic AnyViewHandle.
            tasks_view.into_any_view(cx)
        });
    });
}

Explanation:

• App::new().run(...): This is the entry point for every GPUI application. The closure passed to run executes once the application environment is set up. It receives an AppContext, which provides methods for managing windows, views, and other app-level concerns.
• cx.new_view(...): This method creates a new View instance and wraps it in a ViewHandle. The ViewHandle is how you interact with views in GPUI (e.g., to update them). We initialize our TasksView with some example tasks and an empty input string.
• cx.open_window(...): This opens a new operating system window. The second closure determines the root view that will be displayed within that window. We pass our tasks_view handle, converting it to an AnyViewHandle as required.

If you run this now (cargo run), you should see an empty window with “Loading tasks…” text. Not very exciting yet, but it confirms our basic application structure is working!

5. Rendering the Task List

Now, let’s flesh out the render method of TasksView to display our tasks dynamically. We’ll iterate through self.tasks and create a div element for each one.

// src/main.rs (continued)

// ... (previous code including Task, TasksView structs and their impls, and main function)

// Update the `impl View for TasksView` block with the following `render` method:
impl View for TasksView {
    fn ui_name() -> &'static str {
        "TasksView"
    }

    fn render(&mut self, cx: &mut ViewContext<Self>) -> AnyElement {
        // Register the `handle_add_task` method to be called when the `tasks::Add` action is triggered.
        cx.on_action(self.handle_add_task);

        let tasks_elements = self.tasks.iter().map(|task| {
            let task_id = task.id; // Capture task ID for use in closures

            div()
                .flex_row() // Arrange children in a row (horizontally)
                .items_center() // Vertically center items within the row
                .gap_1() // Add a small gap between items
                .py_1() // Vertical padding for each task row
                .px_2() // Horizontal padding for each task row
                .child(
                    div()
                        .w_4() // Fixed width for our custom checkbox area
                        .child(
                            // GPUI does not have a built-in checkbox element in the same way it has `text_input`.
                            // We typically compose it from other elements, like a div with text or an icon,
                            // and attach event handlers.
                            if task.completed {
                                text("✔").text_color(rgb(0x00FF00)) // Green checkmark for completed
                            } else {
                                text("○").text_color(rgb(0x888888)) // Grey circle for incomplete
                            }
                            // Attach a mouse down handler to toggle completion status
                            .on_mouse_down(MouseButton::Left, move |_, cx| {
                                // ⚡ Quick Note: `move` captures `task_id` by value into the closure.
                                // `cx.update_view` is the correct way to modify view state from an event handler.
                                cx.update_view(cx.view_id(), |this, cx| {
                                    if let Some(task_to_toggle) = this.tasks.iter_mut().find(|t| t.id == task_id) {
                                        task_to_toggle.completed = !task_to_toggle.completed;
                                        cx.notify(); // CRITICAL: Tell GPUI to re-render after state change!
                                    }
                                });
                            })
                        )
                )
                .child(
                    text(task.description.clone()) // Display the task description
                        .text_color(if task.completed {
                            rgb(0x888888) // Grey out completed tasks
                        } else {
                            rgb(0xFFFFFF) // White for active tasks
                        })
                        .flex_grow(1) // Allow the text to take up available horizontal space
                )
                .into_any_element() // Convert our element to a generic `AnyElement`
        }).collect::<Vec<AnyElement>>(); // Collect all task elements into a vector

        div()
            .flex_col() // Arrange main children in a column (vertically)
            .w_full() // Take full width of the parent container
            .h_full() // Take full height of the parent container
            .bg(rgb(0x282C34)) // Dark background color
            .p_4() // Padding around the entire view
            .child(
                div()
                    .text_sm() // Small text size
                    .mb_2() // Margin bottom for spacing
                    .text_color(rgb(0xAAAAAA)) // Light grey text color
                    .child(text("My Tasks")) // Title for the task list
            )
            .children(tasks_elements) // Add our dynamically generated list of task elements
            .into_any_element()
    }
}

Explanation of render method:

• cx.on_action(self.handle_add_task);: This line is vital. It registers our handle_add_task method to be invoked whenever the tasks::Add action is triggered within the application. This registration must happen inside render because it’s tied to the view’s active lifecycle.
• tasks_elements: This Vec<AnyElement> will store the UI representation for each task.
• self.tasks.iter().map(...): We iterate over our tasks vector. For each task:
  • div().flex_row().items_center().gap_1().py_1().px_2(): This creates a horizontal row container for each task. .flex_row() makes its children arrange horizontally, .items_center() aligns them vertically in the middle, and .gap_1() adds a small gap between them. .py_1() and .px_2() add vertical and horizontal padding, respectively.
  • Checkbox Placeholder: We use a div containing text("✔") or text("○") to visually represent a checkbox. This demonstrates how you might compose custom UI elements in GPUI.
  • .on_mouse_down(...): This is how we handle user interaction. When the checkbox placeholder is clicked:
    • cx.update_view(cx.view_id(), |this, cx| { ... }): This is the standard and safe way to modify the state of your view from within an event handler. It provides a mutable reference this to our TasksView instance.
    • this.tasks.iter_mut().find(...): We find the specific task by its id.
    • task_to_toggle.completed = !task_to_toggle.completed;: We toggle its completed status.
    • cx.notify(): Crucially, this tells GPUI that the view’s state has changed and it needs to re-evaluate its render method, causing the UI to update. Without cx.notify(), the UI wouldn’t reflect your state changes!
  • text(task.description.clone()).text_color(...).flex_grow(1): Displays the task description. Its text color changes based on the completed status. .flex_grow(1) makes it expand to take up available horizontal space.
• The outer div: This is the main container for our entire TasksView. It arranges its children in a column (flex_col), takes full width/height, has a dark background, and adds padding.
• children(tasks_elements): This method efficiently adds all the dynamically generated individual task UI elements to the main container.

Now, if you run cargo run, you should see your initial tasks displayed. Clicking the “checkbox” (✔ or ○) should toggle their completion status, and the UI will update in real-time!

6. Adding New Tasks with TextInput

Next, let’s add an input field at the top of our application to allow users to add new tasks. This involves using GPUI’s text_input element and handling its on_submit action.

We already defined the tasks::Add action and TasksView::handle_add_task earlier. Now we just need to integrate the text_input element into our render method.

// src/main.rs (continued)

// ... (previous code including Task, TasksView structs and their impls, and main function)

// Update the `render` method within `impl View for TasksView` again.
// Add the `text_input` element before `children(tasks_elements)`.
impl View for TasksView {
    fn ui_name() -> &'static str {
        "TasksView"
    }

    fn render(&mut self, cx: &mut ViewContext<Self>) -> AnyElement {
        cx.on_action(self.handle_add_task); // Still register the Add action handler

        let tasks_elements = self.tasks.iter().map(|task| {
            // ... (existing task rendering logic from before, unchanged)
            let task_id = task.id;

            div()
                .flex_row()
                .items_center()
                .gap_1()
                .py_1()
                .px_2()
                .child(
                    div()
                        .w_4()
                        .child(
                            if task.completed {
                                text("✔").text_color(rgb(0x00FF00))
                            } else {
                                text("○").text_color(rgb(0x888888))
                            }
                            .on_mouse_down(MouseButton::Left, move |_, cx| {
                                cx.update_view(cx.view_id(), |this, cx| {
                                    if let Some(task_to_toggle) = this.tasks.iter_mut().find(|t| t.id == task_id) {
                                        task_to_toggle.completed = !task_to_toggle.completed;
                                        cx.notify();
                                    }
                                });
                            })
                        )
                )
                .child(
                    text(task.description.clone())
                        .text_color(if task.completed {
                            rgb(0x888888)
                        } else {
                            rgb(0xFFFFFF)
                        })
                        .flex_grow(1)
                )
                .into_any_element()
        }).collect::<Vec<AnyElement>>();

        div()
            .flex_col()
            .w_full()
            .h_full()
            .bg(rgb(0x282C34))
            .p_4()
            .child(
                div()
                    .text_sm()
                    .mb_2()
                    .text_color(rgb(0xAAAAAA))
                    .child(text("My Tasks"))
            )
            .child(
                // The new text input field for adding tasks
                text_input(&self.new_task_input, |this, new_text, cx| {
                    // This closure is called whenever the input text changes.
                    // We update our view's `new_task_input` field.
                    this.new_task_input = new_text.to_string();
                    cx.notify(); // Re-render to ensure the input field visually reflects the updated text
                })
                .on_submit(cx.action_callback(tasks::Add)) // Trigger the `tasks::Add` action when Enter is pressed
                .placeholder("Add a new task...", None) // Placeholder text for the input field
                .px_2()
                .py_1() // Padding
                .rounded_md() // Rounded corners
                .bg(rgb(0x3A3F47)) // Background color
                .text_color(rgb(0xFFFFFF)) // Text color
                .mb_4() // Margin below the input field for spacing
            )
            .children(tasks_elements) // Add our list of task elements below the input
            .into_any_element()
    }
}

Explanation of additions:

• text_input(&self.new_task_input, |this, new_text, cx| { ... }): This creates the text input field.
  • The first argument &self.new_task_input binds the input’s current value to our TasksView’s new_task_input field. This makes the input “controlled” by our view’s state.
  • The closure is called whenever the input text changes (e.g., a user types a character). Inside, we update self.new_task_input and call cx.notify() to ensure the input field visually reflects the change.
• .on_submit(cx.action_callback(tasks::Add)): This is the key interaction. When the user presses Enter in the text_input, it triggers the tasks::Add action. Because we registered self.handle_add_task with cx.on_action, that method will then be called, adding the new task.
• .placeholder(...), .px_2(), .py_1(), .rounded_md(), .bg(...), .text_color(...), .mb_4(): These are styling methods applied to the text_input to make it visually appealing and provide proper spacing.

Now, cargo run again. You should see an input field at the top. Type a task and press Enter – it should appear in the list!

Mini-Challenge: Adding a “Delete Task” Button

You’ve learned how to display tasks, toggle their completion, and add new ones. Now, for a small challenge to solidify your understanding of per-item interactions:

Challenge: Add a “Delete” button (or a clickable “X” icon) next to each task description. When clicked, it should remove that specific task from the tasks list.

Hint:

• You’ll be modifying the render method again, specifically inside the self.tasks.iter().map(...) loop.
• Add a new div (perhaps styled as a small button or an ‘X’) within each task’s flex_row.
• Attach an on_mouse_down handler directly to this new div.
• Inside the handler, use cx.update_view to modify self.tasks. The Vec::retain method is particularly useful for filtering out elements based on a condition (like matching task_id).
• Don’t forget cx.notify() after modifying the state!

Design Choice for Per-Item Actions: For this “Delete Task” challenge, we will use a direct on_mouse_down handler attached to the delete button itself, rather than defining a new global gpui::actions!(tasks, [Delete]) and cx.on_action handler.

• Why? While global actions are excellent for application-wide commands (like “Add New Task” which can be triggered from an input’s on_submit or a menu item), for actions that are specific to a particular item in a list (like deleting this task), it’s often more straightforward and localized to handle the event directly on the UI element that represents that item. The task_id is readily available within the map loop’s closure, making it easy to target the correct task for deletion without needing to pass payloads through a global action system. This keeps the logic for each task self-contained.

What to observe/learn: This challenge reinforces state mutation, handling events for individual items, and dynamic UI updates for list items. You’ll see how easy it is to remove elements from a list and have the UI automatically reflect the change.

// src/main.rs (continued - additions and modifications)

// ... (previous code, including Task struct and impl, TasksView struct and impl, TasksView::handle_add_task impl)

// Full `main` function (unchanged from previous steps)
fn main() {
    App::new().run(|cx: &mut AppContext| {
        let tasks_view = cx.new_view(|cx| TasksView {
            tasks: vec![
                Task::new(0, "Learn GPUI basics".to_string()),
                Task::new(1, "Build a task list".to_string()),
            ],
            next_task_id: 2,
            new_task_input: String::new(),
        });

        cx.open_window(WindowOptions::default(), |cx| {
            tasks_view.into_any_view(cx)
        });
    });
}

// Update the `render` method within `impl View for TasksView` again.
// Add the delete button element inside the task rendering loop.
impl View for TasksView {
    fn ui_name() -> &'static str {
        "TasksView"
    }

    fn render(&mut self, cx: &mut ViewContext<Self>) -> AnyElement {
        cx.on_action(self.handle_add_task); // Still register the Add action handler

        let tasks_elements = self.tasks.iter().map(|task| {
            let task_id = task.id; // Capture task ID for use in closures

            div()
                .flex_row()
                .items_center()
                .gap_1()
                .py_1()
                .px_2()
                .child(
                    div()
                        .w_4()
                        .child(
                            if task.completed {
                                text("✔").text_color(rgb(0x00FF00))
                            } else {
                                text("○").text_color(rgb(0x888888))
                            }
                            .on_mouse_down(MouseButton::Left, move |_, cx| {
                                cx.update_view(cx.view_id(), |this, cx| {
                                    if let Some(task_to_toggle) = this.tasks.iter_mut().find(|t| t.id == task_id) {
                                        task_to_toggle.completed = !task_to_toggle.completed;
                                        cx.notify();
                                    }
                                });
                            })
                        )
                )
                .child(
                    text(task.description.clone())
                        .text_color(if task.completed {
                            rgb(0x888888)
                        } else {
                            rgb(0xFFFFFF)
                        })
                        .flex_grow(1)
                )
                .child(
                    // New Delete button/icon
                    div()
                        .ml_2() // Margin left to separate from description
                        .px_2()
                        .py_1()
                        .rounded_md()
                        .bg(rgb(0xCC3333)) // Red background for delete
                        .text_color(rgb(0xFFFFFF)) // White text
                        .child(text("X")) // Simple 'X' for delete
                        .on_mouse_down(MouseButton::Left, move |_, cx| {
                            // ⚠️ What can go wrong: Forgetting `cx.notify()` after removing an item!
                            cx.update_view(cx.view_id(), |this, cx| {
                                // `Vec::retain` keeps only elements for which the closure returns `true`.
                                // This effectively removes the task with the matching `task_id`.
                                this.tasks.retain(|t| t.id != task_id);
                                cx.notify(); // State changed, re-render!
                            });
                        })
                )
                .into_any_element()
        }).collect::<Vec<AnyElement>>();

        div()
            .flex_col()
            .w_full()
            .h_full()
            .bg(rgb(0x282C34))
            .p_4()
            .child(
                div()
                    .text_sm()
                    .mb_2()
                    .text_color(rgb(0xAAAAAA))
                    .child(text("My Tasks"))
            )
            .child(
                text_input(&self.new_task_input, |this, new_text, cx| {
                    this.new_task_input = new_text.to_string();
                    cx.notify();
                })
                .on_submit(cx.action_callback(tasks::Add))
                .placeholder("Add a new task...", None)
                .px_2()
                .py_1()
                .rounded_md()
                .bg(rgb(0x3A3F47))
                .text_color(rgb(0xFFFFFF))
                .mb_4()
            )
            .children(tasks_elements)
            .into_any_element()
    }
}

Common Pitfalls & Troubleshooting

Building with an actively developed framework like GPUI can sometimes lead to unexpected issues. Here are a few common pitfalls and how to troubleshoot them:

1. UI Not Updating After State Change:

   • Symptom: You’ve modified self.tasks or self.new_task_input, but the UI doesn’t visually reflect the change.
   • Cause: You likely forgot to call cx.notify() after changing your view’s state within cx.update_view. GPUI needs to be explicitly told when a re-render is required because it doesn’t automatically detect changes to your Rust data structures.
   • Fix: Always ensure cx.notify() is called immediately after any state mutation within a cx.update_view closure that should trigger a UI update.

2. Panics Related to ViewContext or AppContext:

   • Symptom: Your application crashes with messages like “tried to update view from incorrect context” or similar runtime errors.
   • Cause: You’re attempting to modify a View’s state (e.g., self.tasks.push(...)) or perform AppContext operations (like opening a new window) outside of the designated update_view or run closures. GPUI enforces strict rules about when and where state can be modified to maintain thread safety and consistency across its asynchronous architecture.
   • Fix: Ensure all view-specific state modifications happen within cx.update_view(...) closures for Views, or directly within the App::new().run(...) closure (or methods called from it) for app-level setup and management.

3. Unstable APIs and Breaking Changes:

   • Symptom: Your code that compiled and worked yesterday suddenly doesn’t compile after cargo update, or you see warnings about deprecated methods.
   • Cause: As of 2026-05-24, GPUI is under very active development. APIs in the main branch can and do change frequently without prior notice.
   • Fix:
     • Consult the Zed editor’s source code: This is the most authoritative and up-to-date source for how GPUI is currently used. Look specifically at the crates/gpui directory and how the zed editor itself uses GPUI for its UI components. This is often more current than any standalone documentation.
     • Check the gpui crate’s README.md: While not always exhaustive, it often contains important notes or examples of recent changes.
     • Review cargo update output: Pay close attention to warnings or errors that indicate specific API changes or deprecations.
     • Embrace the learning curve: Working with cutting-edge frameworks means adapting to changes. This is part of the exciting journey of contributing to or building with rapidly evolving technology!

4. Styling Not Applying as Expected:

   • Symptom: Your div().bg(rgb(0xFF0000)) doesn’t make the background red, or layout properties like flex_grow or gap seem to be ignored.
   • Cause: GPUI’s styling system is powerful and declarative but can be particular. Ensure you’re applying styles to the correct element in the hierarchy. Sometimes a parent’s styling (e.g., flex_col) might override or constrain a child’s (e.g., flex_grow). Incorrect w_full() or h_full() on parent elements can also lead to children not having space to grow.
   • Fix: Use visual debugging techniques. Temporarily add div().border() or div().bg(rgb(0x0000FF)) to intermediate elements to visually debug where elements are actually rendering and what space they occupy. Check the order of your styling calls, as some properties might override others.

Summary

Congratulations! You’ve successfully built a basic but functional Task List Manager with GPUI. In this chapter, you learned how to:

• Model application data using Rust structs (Task).
• Manage state within a GPUI View (TasksView), holding a collection of tasks.
• Dynamically render lists of UI elements based on your view’s state, using the map iterator and children() method.
• Handle user input using text_input to capture new task descriptions.
• Process actions like adding tasks (on_submit triggering a global tasks::Add action) and toggling/deleting individual tasks (on_mouse_down with direct cx.update_view calls).
• Implement basic styling for layout (flex_row, flex_col, gap) and appearance (bg, text_color, rounded_md).
• Debug common issues associated with GPUI’s reactive model and its active development status.

This project provided a solid foundation for building more complex interactive applications. You’ve now moved beyond static examples and understand the core loop of state management, rendering, and interaction in GPUI.

In the next chapter, we’ll explore more advanced UI components, custom styling techniques, and perhaps even delve into how to integrate platform services to make our applications richer. Keep experimenting with your task list – try adding a filter, sorting, or persisting tasks to a file!

References

• GPUI README.md on GitHub
• Zed Editor Source Code (crates/gpui)
• GPUI Tutorial by Hedge-Ops (Note: This tutorial might not always reflect the absolute latest main branch changes but is good for conceptual understanding.)
• Rust std::vec::Vec::retain Documentation
• GPUI elements module (explore source for available elements and methods)

This page is AI-assisted and reviewed. It references official documentation and recognized resources where relevant.