Let's say I have a component with a scrollable subcomponent, and I want to expose the ability to scroll:
const MyComponent = (props) => {
return <ScrollView ... />
}
I want to be able to do
<MyComponent ref={myRef} />
...
myRef.scrollTo({x: 0});
So I need a way to forward the ref to the <ScrollView>
. Let's try putting the ref on the props:
const MyComponent = (props) => {
return <ScrollView ref={props.scrollRef} ... />
}
...
<MyComponent scrollRef={myRef} />
...
myRef.scrollTo({x: 0});
I just tried that with React Native on iOS, and it indeed works. I see several advantages over React.forwardRef
:
What's the advantage of React.forwardRef
? Why was it added in React 16.3?
The forwardRef method in React allows parent components to move down (or “forward”) refs to their children. ForwardRef gives a child component a reference to a DOM entity created by its parent component in React. This helps the child to read and modify the element from any location where it is used.
The only way to pass a ref to a function component is using forwardRef. When using forwardRef, you can simply pass the ref to a DOM element, so the parent can access it like in example 1, or you could create an object with fields and methods using the useImperativeHandle hook, which would be similar to eample 2.
Refs are a function provided by React to access the DOM element and the React element that you might have created on your own. They are used in cases where we want to change the value of a child component, without making use of props and all.
The forwardRef hooks allows React users to pass refs to child components. The ref can be created and referenced with useRef or createRef and then passed in a parent component. Using forwardRef instead of useRef is useful when a ref needs to be accessed in a parent component.
Note that there is no difference between using another named prop like innerRef
FOR FORWARDING, it works the same.
Since React moved toward function components (hooks) you might want to refactor the class component code to a function component without breaking the API.
// Refactor class component API to function component using forwardRef
<Component ref={myRef} />
React.forwardRef
will be your only option (further explained in details).
As a library author you may want a predictable API for ref
forwarding.
For example, if you implemented a Component
and someone wants to attach a ref to it, he has two options depending on your API:
<Component innerRef={myRef} />
innerRef
attached? We can't know, should be mentioned in the API or we console.log(myRef.current)
<Component ref={myRef} />
ref
prop used on HTML elements, commonly attached to the inner wrapper component.Notice that React.forwardRef
can be used for function component and HOC (for class component see alternative below).
Ref forwarding is not limited to DOM components. You can forward refs to class component instances, too.
For function components, forwardRef
sometimes comes with useImperativeHandle
combo (in class component you just call the class methods on ref instance: ref.current.myAttr()
.
// Same usage
<Component ref={myRef} />
const Component = React.forwardRef((props, ref) => {
// you can forward ref <div ref={ref} />
// you can add custom attributes to ref instance with `useImperativeHandle`
// like having ref.myAttribute() in addition to ones attached to other component.
});
Important behavior of ref
prop without forwardRef
.
For the class component, this code alone will attach the ref to CLASS INSTANCE which is not useful by itself and need another ref for forwarding:
// usage, passing a ref instance myRef to class Component
<Component ref={myRef} />
Full example, check the logs:
// We want to forward ref to inner div
class ClassComponent extends React.Component {
innerRef = React.createRef();
render() {
// Notice that you can't just `this.props.ref.current = node`
// You don't have `ref` prop, it always `undefined`.
return <div ref={this.innerRef}>Hello</div>;
}
}
const Component = () => {
const ref = React.useRef();
useEffect(() => {
// The ref attached to class instance
console.log(ref.current);
// Access inner div through another ref
console.log(ref.current.innerRef);
}, []);
return <ClassComponent ref={ref} />;
};
In function components, it won't even work because functions don't have instances.
By default, you may not use the ref attribute on function components because they don’t have instances. [1]
ref
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