小程序實現手寫簽名

發表時間：2022-7-26

發布人：葵宇科技

浏覽次數：42

在微信小程序上實現手寫簽名，獲取canvascontext新版本和(hé)舊版本有點坑，新版本在獲取canvas後如(rú)果頁面有滑動(dòng)，則簽名坐(zuò)标出現異常(在微信開發者工具上會出現2022-2-17)，但是在真機上即使滑動(dòng)也不會出現異常，為了防止出現問(wèn)題，暫時使用舊版本獲取canvascontext

1.效果圖

2.相關(guān)代碼

1.canvas代碼

新版2d canvas

<canvas
  id="canvas"
  class="canvas"
  canvas-id="canvas"
  type="2d"
  :disable-scroll="true"
  @touchstart="handleTouchStart"
  @touchmove="handleTouchMove"
  @touchend="handleTouchEnd"
  @touchcancel="handleTouchCancel"
></canvas>

舊版canvas

<canvas
  class="canvas"
  canvas-id="canvas"
  :disable-scroll="true"
  @touchstart="handleTouchStart"
  @touchmove="handleTouchMove"
  @touchend="handleTouchEnd"
  @touchcancel="handleTouchCancel"
></canvas>

2.js相關(guān)

獲取新版2d canvas對象

const query = uni.createSelectorQuery().in(this);
query.select('.canvas').node(res => {
  const {
      _width,
      _height
  } = res.node;
  
  /* 獲取canvas wxml節點 */
  this.canvas = res.node;
  this.canvasWidth = _width;
  this.canvasHeight = _height;
  /* 獲取canvas 2dcontext */
  this.canvasContext= this.canvas.getContext('2d');
  
  /* 縮放設置canvas畫布大小，防止筆迹錯位 */
  const ratio = wx.getSystemInfoSync().pixelRatio;
  this.canvas.width = this.canvasWidth * ratio;
  this.canvas.height = this.canvasHeight * ratio;
  this.canvasContext.scale(ratio, ratio);
  
  /* 設置線條顔色 */
  this.canvasContext.strokeStyle = '#2A2A2A';
  /* 設置線條粗細 */
  this.canvasContext.lineWidth = 4;
  /* 設置線條的結束端點樣式 */
  this.canvasContext.lineCap = 'round';
}).exec()

縮放設置canvas畫布大小，防止筆迹錯位，這點和(hé)頁面滑動(dòng)沒有關(guān)系，不設置也會導緻坐(zuò)标錯位

const ratio = wx.getSystemInfoSync().pixelRatio;
this.canvas.width = this.canvasWidth * ratio;
this.canvas.height = this.canvasHeight * ratio;
this.canvasContext.scale(ratio, ratio);

舊版本獲取canvas

this.canvasContext = uni.createCanvasContext('canvas', this);
/* 設置線條顔色 */
this.canvasContext.setStrokeStyle('#2A2A2A');
/* 設置線條粗細 */
this.canvasContext.setLineWidth(4);
/* 設置線條的結束端點樣式 */
this.canvasContext.setLineCap('round');

簽名js方法，新版本和(hé)舊版本隻有一個(gè)draw的區别，新版本不需要使用draw方法

/* 觸摸開始 */
handleTouchStart(e) {
  this.drawStartX = e.changedTouches[0].x;
  this.drawStartY = e.changedTouches[0].y;
    this.canvasContext.beginPath();
},
/* 觸摸移動(dòng) */
handleTouchMove(e) {
    /* 記錄當前位置 */
    const tempX = e.changedTouches[0].x;
    const tempY = e.changedTouches[0].y;

    /* 畫線 */
    this.canvasContext.moveTo(this.drawStartX, this.drawStartY);
    this.canvasContext.lineTo(tempX, tempY);
    this.canvasContext.stroke();

    /* 舊版draw方法，新版本不需要draw */
    this.canvasContext.draw(true);

    /* 重新記錄起始位置 */
    this.drawStartX = tempX;
    this.drawStartY = tempY;
},
/* 觸摸結束 */
handleTouchEnd(e) {
    this.canvasContext.save();
},
/* 觸摸取消 */
handleTouchCancel(e) {
    this.canvasContext.save();
},
/* 清空畫布 */
clearCanvas() {
    this.canvasContext.clearRect(0, 0, this.canvasWidth, this.canvasHeight);
},

canvas生成本地圖片(我這裡封裝了組件，需要傳入this防止this指向異常)

/* 生成簽名圖片 */
generateSignImage() {
    return new Promise((resolve, reject) => {
        uni.canvasToTempFilePath({
          x: 0,
          y: 0,
          // canvas: this.canvas, // 新版
          canvasId: 'canvas', // 舊版使用id
          width: this.canvasWidth,
          height: this.canvasHeight,
          destWidth: this.canvasWidth,
          destHeight: this.canvasHeight,
          fileType: 'png',
          quality: 1,
          success: res => {
              resolve(res.tempFilePath)
          },
          fail: err => {
              reject(err);
          }
        }, this)
    })
},

新版本的canvas主要是canvas wxml節點和(hé)canvas context中(zhōng)做了區分，舊版則隻有一個(gè)canvas context就可(kě)以做全部的操作，在生成圖片時，新版本是傳入wxml對象，舊版本則是傳入唯一canvasId，新版本canvas取消了draw方法