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636692507e
* Convert components concept docs from SC to FC - moved struct components to advanced topics - added docs about HOC for Suspense and Context - added a ease-in topic before components that introduces HTML/CSS/JS in yew - edit components concept to use function components * translations * fix todo links * fix tests * spelling bee
68 lines
1.9 KiB
Plaintext
68 lines
1.9 KiB
Plaintext
---
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title: "use_state"
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---
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`use_state` is used to manage state in a function component.
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It returns a `UseStateHandle` object which `Deref`s to the currently stored value
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and provides a `set` method to update the value.
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The hook takes a function as input which determines the initial value.
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:::tip Advanced tip
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The setter function is guaranteed to be the same across the entire
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component lifecycle. You can safely omit the `UseStateHandle` from the
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dependents of `use_effect_with_deps` if you only intend to set
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values from within the hook.
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:::
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This hook will always trigger a re-render upon receiving a new state. See
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[`use_state_eq`](#use_state_eq) if you want the component to only
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re-render when the state changes.
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## Example
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```rust
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use std::ops::Deref;
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use yew::{Callback, function_component, html, use_state, Html};
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#[function_component]
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fn StateExample() -> Html {
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let name_handle = use_state(|| String::from("Bob"));
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let name = name_handle.deref().clone();
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let onclick = {
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let name = name.clone();
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Callback::from(move |_| name_handle.set(format!("{}y Jr.", name)))
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};
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html! {
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<div>
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<button {onclick}>{ "Update name" }</button>
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<p>
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<b>{ "My name is: " }</b>
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{ name }
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</p>
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</div>
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}
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}
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```
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:::caution
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The value held in the handle will reflect the value at the time the
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handle is returned by the `use_state`. It is possible that the handle
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does not dereference to an up to date value if you are moving it into a
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`use_effect_with_deps` hook. You can register the
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state to the dependents so the hook can be updated when the value changes.
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:::
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## `use_state_eq`
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This hook has the same effect as `use_state` but will only trigger a
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re-render when the setter receives a value that `prev_state != next_state`.
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This hook requires the state object to implement `PartialEq`.
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