一個基於react的圖片裁剪組件

開始

寫了一年多vue，感受碰到了點瓶頸，學習下react找找感受。恰好最近使用vue寫了個基於cropperJS的圖片裁剪的組件，便花費了幾個晚上的功夫用react再寫一遍。代碼地址，demo地址
項目是使用create-react-app來開發的，省去了不少webpack配置的功夫，支持eslint，自動刷新等功能，使用前npm install並npm start便可。推薦一樣是新學習react的人也用用看。
項目寫的比較簡陋，自定義配置比較差，不過也是完成了裁剪圖片的基本功能，但願能夠幫助到初學react和想了解裁剪圖片組件的朋友。
組件的結構是這樣的。

<!--Cropper-->

     <div>
      <ImageUploader handleImgChange={this.handleImgChange} getCropData={this.getCropData}/>
       <div className="image-principal">
         <img src={this.state.imageValue} alt="" className="img" ref="img" onLoad={this.setSize}/>
         <SelectArea ref="selectArea"></SelectArea>
       </div>
     </div>
<!--ImageUploader     -->
      <form className="image-upload-form" method="post" encType="multipart/form-data" >
        <input type="file" name="inputOfFile" ref="imgInput" id="imgInput" onChange={this.props.handleImgChange}/>
        <button onClick={this.props.getCropData}>獲取裁剪參數</button>
      </form>
<!--SelectArea     -->
     <div className="select-area" onMouseDown={ this.dragStart} ref="selectArea" >
       <div className="top-resize" onMouseDown={ event => this.resizeStart(event, 'top')}></div>
       <div className="right-resize" onMouseDown={ event => this.resizeStart(event, 'right')}></div>
       <div className="bottom-resize" onMouseDown={ event => this.resizeStart(event, 'bottom')}></div>
       <div className="left-resize" onMouseDown={ event => this.resizeStart(event, 'left')}></div>
       <div className="right-bottom-resize" onMouseDown={ event => this.resizeStart(event, 'right')}></div>
       <div className="left-top-resize" onMouseDown={ event => this.resizeStart(event, 'left')}></div>
     </div>

ImageUploader & Cropper

ImageUploader主要作的就是上傳圖片，監聽了input的change事件，並調用了父組件Cropper的的handleImgChange方法,該方法設置了綁定到img元素的imageValue，會使得img元素出發load事件。

handleImgChange = e => {
    let fileReader = new FileReader()
    fileReader.readAsDataURL(e.target.files[0])
    fileReader.onload = e => {
      this.setState({...this.state, imageValue: e.target.result})
    }
  }

load事件觸發了Cropper的setSize方法，該方法能夠設置了圖片和裁剪選擇框的初始位置和大小。目前裁剪選擇框是默認設置是大小爲圖片的80%，中間顯示。

setSize = () => {
    let img = this.refs.img
    let widthNum = parseInt(this.props.width, 10)
    let heightNum = parseInt(this.props.height, 10)
    this.setState({
      ...this.state,
      naturalSize: {
        width: img.naturalWidth,
        height: img.naturalHeight
      }
    })
    let imgStyle = img.style
    imgStyle.height = 'auto'
    imgStyle.width = 'auto'
    let principalStyle = ReactDOM.findDOMNode(this.refs.selectArea).parentElement.style
    const ratio = img.width / img.height
    // 設置圖片大小、位置
    if (img.width > img.height) {
      imgStyle.width = principalStyle.width = this.props.width
      imgStyle.height = principalStyle.height = widthNum / ratio + 'px'
      principalStyle.marginTop = (widthNum - parseInt(principalStyle.height, 10)) / 2 + 'px'
      principalStyle.marginLeft = 0
    } else {
      imgStyle.height = principalStyle.height = this.props.height
      imgStyle.width = principalStyle.width = heightNum * ratio + 'px'
      principalStyle.marginLeft = (heightNum - parseInt(principalStyle.width, 10)) / 2 + 'px'
      principalStyle.marginTop = 0
    }
    // 設置選擇框樣式
    let selectAreaStyle = ReactDOM.findDOMNode(this.refs.selectArea).style
    let principalHeight = parseInt(principalStyle.height, 10)
    let principalWidth = parseInt(principalStyle.width, 10)
    if (principalWidth > principalHeight) {
      selectAreaStyle.top = principalHeight * 0.1 + 'px'
      selectAreaStyle.width = selectAreaStyle.height = principalHeight * 0.8 + 'px'
      selectAreaStyle.left = (principalWidth - parseInt(selectAreaStyle.width, 10)) / 2 + 'px'
    } else {
      selectAreaStyle.left = principalWidth * 0.1 + 'px'
      selectAreaStyle.width = selectAreaStyle.height = principalWidth * 0.8 + 'px'
      selectAreaStyle.top = (principalHeight - parseInt(selectAreaStyle.height, 10)) / 2 + 'px'
    }
  }

Cropper上還有一個getCropData方法，方法會打印並返回裁剪參數,

getCropData = e => {
    e.preventDefault()
    let SelectArea = ReactDOM.findDOMNode(this.refs.selectArea).style

    let a = {
      width: parseInt(SelectArea.width, 10),
      height: parseInt(SelectArea.height, 10),
      left: parseInt(SelectArea.left, 10),
      top: parseInt(SelectArea.top, 10)
    }
    a.radio = this.state.naturalSize.width / a.width

    console.log(a)
    return a
  }

SelectArea

從新放一遍selectArea的結構。要注意，.top-resize的cursor屬性是 n-resize，而和left，right，bottom對應的分別是w-resize，e-resize，s-resize

<div className="select-area" onMouseDown={ this.dragStart} ref="selectArea" >
       <div className="top-resize" onMouseDown={ event => this.resizeStart(event, 'top')}></div>
       <div className="right-resize" onMouseDown={ event => this.resizeStart(event, 'right')}></div>
       <div className="bottom-resize" onMouseDown={ event => this.resizeStart(event, 'bottom')}></div>
       <div className="left-resize" onMouseDown={ event => this.resizeStart(event, 'left')}></div>
       <div className="right-bottom-resize" onMouseDown={ event => this.resizeStart(event, 'right')}></div>
       <div className="left-top-resize" onMouseDown={ event => this.resizeStart(event, 'left')}></div>
     </div>

selectArea的state值設爲這樣，selectArea保存拖拽選擇框時的參數，resizeArea保存裁剪選擇框時的參數，container爲.image-principal元素，el爲觸發事件時的event.target。

this.state = {
      selectArea: null,
      el: null,
      container: null,
      resizeArea: null
    }

拖拽選擇框

在.select-area按下鼠標，觸發mouseDown事件，調用dragStart方法。
使用method = e => {}的形式能夠避免在jsx中使用this.method.bind(this)
在這個方法中，首先保存按下鼠標時的鼠標位置，裁剪框與圖片的相對距離和裁剪框的最大位移距離，接着添加事件監聽

dragStart = e => {
    const el = e.target
    const container = this.state.container
    let selectArea = {
      posLeft: e.clientX,
      posTop: e.clientY,
      left: e.clientX - el.offsetLeft,
      top: e.clientY - el.offsetTop,
      maxMoveX: container.offsetWidth - el.offsetWidth,
      maxMoveY: container.offsetHeight - el.offsetHeight,
    }
    this.setState({ ...this.state, selectArea, el})
    document.addEventListener('mousemove', this.moveBind, false)
    document.addEventListener('mouseup', this.stopBind, false)
  }

moveBind和stopBind來自於

this.moveBind = this.move.bind(this)
  this.stopBind = this.stop.bind(this)

move方法,在鼠標移動中根據記錄新的鼠標位置來計算新的相對位置newPosLeft和newPosTop,並控制該值在合理範圍內

move(e) {
    if (!this.state || !this.state.el || !this.state.selectArea) {
      return
    }
    let selectArea = this.state.selectArea
    let newPosLeft = e.clientX- selectArea.left
    let newPosTop = e.clientY - selectArea.top
    // 控制移動範圍
    if (newPosLeft <= 0) {
      newPosLeft = 0
    } else if (newPosLeft > selectArea.maxMoveX) {
      newPosLeft = selectArea.maxMoveX
    }
    if (newPosTop <= 0) {
      newPosTop = 0
    } else if (newPosTop > selectArea.maxMoveY) {
      newPosTop = selectArea.maxMoveY
    }
    let elStyle = this.state.el.style
    elStyle.left = newPosLeft + 'px'
    elStyle.top = newPosTop + 'px'
  }

stop方法，移除事件監聽，清除state,避免方法錯誤調用

stop() {
    document.removeEventListener('mousemove', this.moveBind , false)
    document.removeEventListener('mousemove', this.resizeBind , false)
    document.removeEventListener('mouseup', this.stopBind, false)
    this.setState({...this.state, el: null, resizeArea: null, selectArea: null})
  }

裁剪選擇框

跟拖拽同樣，首先調用resizeStart方法，保存開始裁剪的鼠標位置，裁剪框的尺寸和位置，添加關於resizeBind和stopBind的事件監聽，注意，因爲react的事件機制特色，須要使用stopPropagation來禁止事件冒泡，事件監聽的第三個參數使用false是無效的。

resizeStart = (e, type) => {
    e.stopPropagation()
    const el = e.target.parentElement
    let resizeArea = {
      posLeft: e.clientX,
      posTop: e.clientY,
      width: el.offsetWidth,
      height: el.offsetHeight,
      left: parseInt(el.style.left, 10),
      top: parseInt(el.style.top, 10)
    }
    this.setState({ ...this.state, resizeArea, el})
    this.resizeBind = this.resize.bind(this, type)
    document.addEventListener('mousemove', this.resizeBind, false)
    document.addEventListener('mouseup', this.stopBind, false)
  }

裁剪的方法，將裁剪分爲兩種狀況，一種是右側，下側和右下側的拉伸。另外一種是左側，上側和左上側的拉伸。
第一種狀況下，選擇框的位置是不會變的，只有尺寸會變，處理起來相對簡單。新的尺寸大小爲原大小加上當前的鼠標的位置再減去開始拖拽處的鼠標的位置，若是寬度或者高度有一個超標了，則將尺寸設置爲恰好到邊界的大小。均爲超標，設置爲新的尺寸。
第二種狀況下，選擇框的位置和大小同時會變，要同時控制尺寸和位置不超出邊界。

resize(type, e) {
    if (!this.state || !this.state.el || !this.state.resizeArea) {
      return
    }
    let container = this.state.container
    const containerHeight = container.offsetHeight
    const containerWidth = container.offsetWidth
    const containerLeft = parseInt(container.style.left || 0, 10)
    const containerTop = parseInt(container.style.top || 0, 10)
    let resizeArea = this.state.resizeArea
    let el = this.state.el
    let elStyle = el.style
    if (type === 'right' || type === 'bottom') {
      let length
      if (type === 'right') {
        length = resizeArea.width + e.clientX - resizeArea.posLeft
      } else {
        length = resizeArea.height + e.clientY - resizeArea.posTop
      }
      if (parseInt(el.style.left, 10) + length > containerWidth || parseInt(el.style.top, 10) + length > containerHeight) {
        const w = containerWidth - parseInt(el.style.left, 10)
        const h = containerHeight - parseInt(el.style.top, 10)
        elStyle.width = elStyle.height = Math.min(w, h) + 'px'
      } else {
        elStyle.width = length + 'px'
        elStyle.height = length + 'px'
      }
    } else {
      let posChange
      let newPosLeft
      let newPosTop
      if (type === 'left') {
        posChange = resizeArea.posLeft - e.clientX
      } else {
        posChange = resizeArea.posTop - e.clientY
      }
      newPosLeft = resizeArea.left - posChange
      // 防止過分縮小
      if (newPosLeft > resizeArea.left + resizeArea.width) {
        elStyle.left = resizeArea.left + resizeArea.width + 'px'
        elStyle.top = resizeArea.top + resizeArea.height + 'px'
        elStyle.width = elStyle.height = '2px'
        return
      }
      newPosTop = resizeArea.top - posChange
      // 到達邊界
      if (newPosLeft <= containerLeft || newPosTop < containerTop) {
        // 讓選擇框到圖片最左邊
        let newPosLeft2 = resizeArea.left -containerLeft
        // 判斷頂部會不會超出邊界
        if (newPosLeft2 < resizeArea.top) {
          // 未超出邊界
          elStyle.top = resizeArea.top - newPosLeft2 + 'px'
          elStyle.left = containerLeft + 'px'
        } else {
          // 讓選擇框到達圖片頂部
          elStyle.top = containerTop + 'px'
          elStyle.left = resizeArea.left + containerTop - resizeArea.top + 'px'
        }
      } else {
        if (newPosLeft < 0) {
          elStyle.left = 0;
          elStyle.width = Math.min(resizeArea.width + posChange - newPosLeft, containerWidth) + 'px'
          elStyle.top = newPosTop - newPosLeft;
          elStyle.height = Math.min(resizeArea.height + posChange - newPosLeft, containerHeight) + 'px'
          return;
        }
        if (newPosTop < 0) {
          elStyle.left = newPosLeft - newPosTop;
          elStyle.width = Math.min(resizeArea.width + posChange - newPosTop, containerWidth) + 'px'
          elStyle.top = 0;
          elStyle.height = Math.min(resizeArea.height + posChange - newPosTop, containerHeight) + 'px'
          return;
        }
        elStyle.left = newPosLeft + 'px'
        elStyle.top = newPosTop + 'px'
        elStyle.width = resizeArea.width + posChange + 'px'
        elStyle.height = resizeArea.height + posChange + 'px'
      }
    }
  }

結束

經過這些組件的編寫，感受想要學好react，須要加深對this和事件模型的瞭解，這幾天在這上面踩了很多的坑。若是以爲這篇文章有幫助的話，歡迎star個人項目