Detailed explanation of React using useImperativeHandle to custom expose to parent components

summary

useImperativeHandle is a custom Hook provided by React for explicitly exposing specific instances to parent component in a function component. This article will introduce the basic usage of useImperativeHandle, common application scenarios, and how to deal with its dependencies to help readers fully understand its use.

introduction

In React, communication between components is usually done through props. However, sometimes we want to be able to directly call certain methods of the child component or access the state inside it in the parent component. To achieve this, React provides a powerful custom Hook with useImperativeHandle.

main body

Basic usage of useImperativeHandle

useImperativeHandle allows us to define instance methods that can be used directly in the parent component. It receives two parameters: ref and a callback function that returns an object containing the methods or properties we wish to expose to the parent component.

import React, { useRef, useImperativeHandle } from 'react';

// Subcomponentsconst ChildComponent = ((props, ref) => {
  const internalMethod = () => {
    // Internal method logic of subcomponents  };

  // Expose internalMethod to the parent component  useImperativeHandle(ref, () => ({
    callInternalMethod: internalMethod
  }));

  return <div>Child Component</div>;
});

// Parent componentconst ParentComponent = () => {
  const childRef = useRef();

  const handleClick = () => {
    ();
  };

  return (
    <div>
      <button onClick={handleClick}>Call Child Method</button>
      <ChildComponent ref={childRef} />
    </div>
  );
};

In the above code, we use useImperativeHandle to expose the internalMethod method of the parent component ParentComponent child component ChildComponent. By using forwardRef and useRef, we can get a reference to the child component and call its methods.

Dependency processing of useImperativeHandle

useImperativeHandle also provides processing of dependencies, i.e. the third parameter. With this parameter, we can set the dependency array, and the exposure of the method or attribute will be recalculated and updated only when the dependency changes.

useImperativeHandle(ref, () => ({
  callInternalMethod: internalMethod
}), [internalMethod]); // Pass in dependency array

In the example above, we pass in internalMethod as a dependency, and the methods exposed to the parent component will be recalculated and updated only when the internalMethod changes.

Dependencies processing can help us optimize performance and reduce unnecessary calculations and updates. However, be careful to avoid passing functions in dependency arrays, as it will cause the dependencies to change every time they are re-rendered.

Note: If the value of useState is used within the exposed method, the value needs to be added to the dependency, otherwise the exposed method uses the initialized value.

Application scenarios of useImperativeHandle

Encapsulation of third-party libraries: When we need to encapsulate a third-party library or component, expose a specific method to the outside, rather than exposing the entire instance to the parent component, we can use useImperativeHandle.

Form Verification: In a form component, we may need a method to trigger form validation in the parent component. By using useImperativeHandle, we can expose the verification method to the parent component to be called at the appropriate time.

Animation control: In some cases, we may need to control the animation effects of children in the parent component. By using useImperativeHandle, we can expose animation control methods to the parent component to achieve more granular animation control.

Other scenarios: Anyone who needs to access the child component instance method or property directly in the parent component can consider using useImperativeHandle.

in conclusion

Using useImperativeHandle in React function components can easily expose instance methods of child components to parent components. This method makes communication between components more flexible and direct. However, we should use useImperativeHandle with caution and minimize coupling between components, following the principle of one-way data flow.

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