javascript - 我在 react 中使用scrollLeft，但它没有将其值设置为元素

Question

我正在鼠标移动时制作一个可拖动的 slider ，我正在获取起始鼠标位置并用当前鼠标位置减去它，并将其设置为状态并将其添加到元素滚动左侧，但它不起作用

onMouseMove = (e) => {
        if (!this.isDown) {
            return
        }
        e.preventDefault();
        var x = e.pageX - this.slider.current.offsetLeft;
        var walk = this.startX - x;
        var z = this.scrollLeft - walk;
        console.log( this.slider.current.scrollLeft);
        this.setState({ left:  this.state.left + z })
        var slider = document.querySelector('.slider-container');
        // console.log(slider);

        slider.scrollLeft=this.state.left
    }

Answer 1

这是因为 this.setState 没有直接执行。它被排队等待 react 处理。回调可用于确定何时完成:

onMouseMove = (e) => {
    if (!this.isDown) {
        return
    }
    e.preventDefault();
    var x = e.pageX - this.slider.current.offsetLeft;
    var walk = this.startX - x;
    var z = this.scrollLeft - walk;
    console.log( this.slider.current.scrollLeft);
    this.setState({ left:  this.state.left + z }, () => {
        var slider = document.querySelector('.slider-container');
        // console.log(slider);

        this.slider.scrollLeft=this.state.left
    })
}

查看以下示例:

import React from "react";
import ReactDOM from "react-dom";

class App extends React.Component {
  p = 0;
  constructor(props) {
    super(props);
    this.state = {
      left: 0
    };

    this.slider = React.createRef();
  }

  onMouseDown = e => {
    e.persist();
    this.isDown = true;

    this.startX = e.pageX - this.slider.current.offsetLeft;
    this.scrollLeft = this.slider.current.scrollLeft;
    this.slider.current.style.cursor = "grabbing";
    // console.log(
    //   e.pageX - this.slider.current.offsetLeft,
    //   this.slider.current.scrollLeft
    // );
  };
  onMouseLeave = () => {
    this.isDown = false;
  };
  onMouseUp = () => {
    this.isDown = false;
    this.slider.current.style.cursor = "pointer";
  };
  onMouseMove = e => {
    if (!this.isDown) {
      return;
    }

    e.preventDefault();
    var x = e.pageX - this.slider.current.offsetLeft;
    var walk = (this.startX - x) / 20;
    var z = this.slider.current.scrollLeft - walk;

    this.setState({ left: this.state.left + z }, () => {
      this.slider.current.scrollLeft = this.state.left;
    });
  };
  goLeftPercent = () => {
    return {
      transform: `translatex(${this.p}px)`,
      transition: "0.3s"
    };
  };
  goLeft = () => {
    if (this.p < -970) {
      return;
    }
    this.p += -326;
    this.setState({ left: this.p, percent: true });
  };
  goRight = () => {
    if (this.p === 0) {
      return;
    }
    this.p += 326;
    this.setState({ left: this.p });
  };

  mouseMove = () => {
    if (this.state.left > 0) {
      this.setState({ left: 0 });
      return;
    } else if (this.state.left < -980) {
      this.setState({ left: -980 });
      return;
    }
    return {
      transform: `translatex(${this.state.left}px)`
    };
  };

  render() {
    const slides = [
      { src: "", name: "Livingroom1" },
      { src: "", name: "Livingroom2" }
    ];

    return (
      <div className="slider">
        <div className="slider-wrapper">
          <div
            onMouseDown={this.onMouseDown}
            style={this.state.percent ? this.goLeftPercent() : this.mouseMove()}
            onMouseUp={this.onMouseUp}
            onMouseLeave={this.onMouseLeave}
            onMouseMove={this.onMouseMove}
            ref={this.slider}
            className="slider-container test"
          >
            {slides.map(slide => (
              <div className="slide">
                <img src={slide.src} alt="" />
                <div className="overlay">
                  <h1>{slide.name}</h1>
                </div>
              </div>
            ))}
          </div>
        </div>
        <div className="slider-arrows">
          <div onClick={this.goLeft} className="arrow-wrapper">
            {" "}
            Left
            <div className="arrow-left">
              <div className="arrow-top" /> <div className="arrow-bottom" />{" "}
            </div>
          </div>
          <div onClick={this.goRight} className="arrow-right">
            Right
          </div>
        </div>
      </div>
    );
  }
}

ReactDOM.render(<App />, document.getElementById("app"));

互动演示:https://codesandbox.io/s/sad-murdock-8f766