React useImperativeHandle: Refカスタマイズパターンをマスターする

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

const MyInput = forwardRef((props, ref) => {
  return <input ref={ref} {...props} />; // Assign the ref to the input element
});

const ParentComponent = () => {
  const inputRef = useRef(null);

  const focusInput = () => {
    inputRef.current.focus(); // Imperatively focus the input
  };

  return (
    <div>
      <MyInput ref={inputRef} />
      <button onClick={focusInput}>Focus Input</button>
    </div>
  );
};

export default ParentComponent;

            

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

const MyInput = forwardRef((props, ref) => {
  const inputRef = useRef(null);

  useImperativeHandle(ref, () => ({
    focus: () => {
      inputRef.current.focus();
    },
    blur: () => {
      inputRef.current.blur();
    },
  }), []);

  return <input ref={inputRef} {...props} />; // Assign the ref to the input element
});

const ParentComponent = () => {
  const inputRef = useRef(null);

  const focusInput = () => {
    inputRef.current.focus(); // Imperatively focus the input
  };

  return (
    <div>
      <MyInput ref={inputRef} />
      <button onClick={focusInput}>Focus Input</button>
    </div>
  );
};

export default ParentComponent;

            

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

const VideoPlayer = forwardRef((props, ref) => {
  const videoRef = useRef(null);
  const [isPlaying, setIsPlaying] = useState(false);

  const play = () => {
    videoRef.current.play();
    setIsPlaying(true);
  };

  const pause = () => {
    videoRef.current.pause();
    setIsPlaying(false);
  };

  useImperativeHandle(ref, () => ({
    play,
    pause,
    togglePlay: () => {
      if (isPlaying) {
        pause();
      } else {
        play();
      }
    },
  }), [isPlaying]);

  return (
    <div>
      <video ref={videoRef} src={props.src} controls={false} />
      <button onClick={() => ref.current.togglePlay()}>Toggle Play</button>
    </div>
  );
});

const ParentComponent = () => {
  const playerRef = useRef(null);

  return (
    <div>
      <VideoPlayer ref={playerRef} src="video.mp4" />
      <button onClick={() => playerRef.current.play()}>Play Video</button>
    </div>
  );
};

export default ParentComponent;

            

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

const AnimatedBox = forwardRef((props, ref) => {
  const boxRef = useRef(null);
  const [isAnimating, setIsAnimating] = useState(false);

  const animate = () => {
    setIsAnimating(true);
    // Add animation logic here (e.g., using CSS transitions)
    setTimeout(() => {
      setIsAnimating(false);
    }, 1000); // Duration of the animation
  };

  useImperativeHandle(ref, () => ({
    animate,
  }), []);

  return (
    <div
      ref={boxRef}
      style={{
        width: 100,
        height: 100,
        backgroundColor: 'blue',
        transition: 'transform 1s ease-in-out',
        transform: isAnimating ? 'translateX(100px)' : 'translateX(0)',
      }}
    />
  );
});

const ParentComponent = () => {
  const boxRef = useRef(null);

  return (
    <div>
      <AnimatedBox ref={boxRef} />
      <button onClick={() => boxRef.current.animate()}>Animate Box</button>
    </div>
  );
};

export default ParentComponent;

            

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

const InputField = forwardRef((props, ref) => {
  const inputRef = useRef(null);
  const [error, setError] = useState('');

  const validate = () => {
    if (inputRef.current.value === '') {
      setError('This field is required.');
      return false;
    } else {
      setError('');
      return true;
    }
  };

  useImperativeHandle(ref, () => ({
    validate,
  }), []);

  return (
    <div>
      <input ref={inputRef} {...props} />
      {error && <p style={{ color: 'red' }}>{error}</p>}
    </div>
  );
});

const ParentForm = () => {
  const nameRef = useRef(null);
  const emailRef = useRef(null);

  const handleSubmit = () => {
    const isNameValid = nameRef.current.validate();
    const isEmailValid = emailRef.current.validate();

    if (isNameValid && isEmailValid) {
      alert('Form is valid!');
    } else {
      alert('Form is invalid.');
    }
  };

  return (
    <form>
      <InputField ref={nameRef} type="text" placeholder="Name" />
      <InputField ref={emailRef} type="email" placeholder="Email" />
      <button type="button" onClick={handleSubmit}>Submit</button>
    </form>
  );
};

export default ParentForm;

            

              
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