What Methods Are Included in the Yew Component Lifecycle and What Is the Purpose of Each Method?

Yew Component Lifecycle Explained

The Yew component lifecycle is similar to React but implemented using Rust's trait system. Understanding the component lifecycle is crucial for building efficient applications.

Main Lifecycle Methods

1. create()

• Timing: Called when the component is first created
• Purpose: Initialize component state
• Return Value: Returns the initial state of the component
• Example:

rust
impl Component for MyComponent {
    type Message = Msg;
    type Properties = Props;
    
    fn create(ctx: &Context<Self>) -> Self {
        Self {
            counter: 0,
            value: String::new(),
        }
    }
}

2. view()

• Timing: Called whenever state or properties change
• Purpose: Render the component's UI
• Return Value: Returns Html type
• Example:

rust
fn view(&self, ctx: &Context<Self>) -> Html {
    html! {
        <div class="container">
            <h1>{ "Counter: " }{ self.counter }</h1>
            <button onclick={ctx.link().callback(|_| Msg::Increment)}>
                { "Increment" }
            </button>
        </div>
    }
}

3. update()

• Timing: Called when a message is received
• Purpose: Handle state updates
• Return Value: Returns bool indicating whether re-rendering is needed
• Example:

rust
fn update(&mut self, ctx: &Context<Self>, msg: Self::Message) -> bool {
    match msg {
        Msg::Increment => {
            self.counter += 1;
            true  // Needs re-rendering
        }
        Msg::NoOp => false, // No re-rendering needed
    }
}

4. changed()

• Timing: Called when component props change
• Purpose: Decide whether to update the component based on new props
• Return Value: Returns bool indicating whether re-rendering is needed
• Example:

rust
fn changed(&mut self, ctx: &Context<Self>, _old_props: &Self::Properties) -> bool {
    // Only re-render when important properties change
    true
}

5. rendered()

• Timing: Called after the component is rendered to the DOM
• Purpose: Perform DOM operations, initialize third-party libraries, etc.
• Example:

rust
fn rendered(&mut self, ctx: &Context<Self>, first_render: bool) {
    if first_render {
        // Initialization operations after first render
    }
}

6. destroy()

• Timing: Called when the component is removed from the DOM
• Purpose: Clean up resources, cancel subscriptions, etc.
• Example:

rust
fn destroy(&mut self, ctx: &Context<Self>) {
    // Clean up timers, cancel network requests, etc.
}
}

Lifecycle Flow Diagram

shell
Create Component
    ↓
create() → Initialize State
    ↓
view() → Render UI
    ↓
rendered() → DOM Operations
    ↓
[Receive Message/Props Change]
    ↓
update() / changed() → Update State
    ↓
view() → Re-render
    ↓
rendered() → DOM Update
    ↓
[Component Unmount]
    ↓
destroy() → Clean Up Resources

Best Practices

1. Avoid complex calculations in view(): Move computation logic to update() or separate methods
2. Use changed() wisely: Avoid unnecessary re-renders
3. Clean up resources promptly: Clean up timers, event listeners, etc. in destroy()
4. Use rendered() for DOM operations: Ensure DOM has finished rendering