微信小程序 - 曲线图

最近要做微信小程序，项目中需要曲线图显示数据，所以在网上看了一下找了很久都没有找到一个，不知道是我查找的姿势不对，还是什么的。所以就自己做了一个曲线图，现在分享给大家。

wxml代码：

　　

<canvas canvas-id='curve-img' style='width:{{canvasWidth}}px;height:{{canvasHeight}}px;'></canvas>

　　

js 代码：

Page({
  canvasIdErrorCallback: function(e) {
    console.error(e);
  },
  /**
   * 页面的初始数据
   */
  data: {
    canvasWidth: 0,
    canvasHeight: 300,
    canvasDefaultVal: {
      maxVal: 0,
      totalData: 0,
      data: []
    }
  },

  /**
   * 生命周期函数--监听页面加载
   */
  onLoad: function(e) {
    var _this = this;
    wx.getSystemInfo({
      success: function(res) {
        _this.setData({
          canvasWidth: res.windowWidth - 3
        });
      },
    })
  },

  /**
   * 生命周期函数--监听页面初次渲染完成
   */
  onReady: function() {
    var ctx = wx.createCanvasContext("curve-img");
    var dataValue = [
      ["10-22", 425],
      ["10-23", 960],
      ["10-24", 700],
      ["10-25", 880],
      ["10-26", 695],
      ["10-27", 375],
      ["10-28", 775]
    ];
    //初始化 画布
    this.oncInit(ctx, dataValue);
    // 绘制图形表与数据连线
    this.onDrawingXY(ctx);

    ctx.draw();
  },
  oncInit: function(ctx, data) {
    // 设置X轴默认总值
    let totalX = 7;
    // 设置最大值、宽度、高度值
    var maxVal = 0,
      totalData = data.length;
    var cWidth = this.data.canvasWidth,
      cHeight = this.data.canvasHeight;
    for (let i = 0; i < totalData; i++) {
      let val = parseInt(data[i][1]);
      if (val > maxVal) {
        maxVal = val;
      }
    }
    maxVal+=50;

    // 初始化图
    ctx.setFillStyle = "#888888";
    ctx.beginPath();
    ctx.setLineWidth(1);
    ctx.moveTo(3, cHeight);
    ctx.lineTo(cWidth + 3, cHeight);
    ctx.stroke();
    ctx.closePath();
    // 设置全局变量
    this.setData({
      canvasDefaultVal: {
        data: data,
        maxVal: maxVal,
        maxValMean: maxVal / totalX,
        totalData: totalData,
        totalX: totalX,
        totalY: totalData,
        xMarign: cHeight / (totalX + 1),
        yMarign: cWidth / totalData
      },
      canvasHeight: cHeight
    });

  },
  onDrawingXY: function(ctx) {
    var xMarign = 0,
      yMarign = 0,
      data = this.data.canvasDefaultVal.data,
      mean = 0,
      meanVal = parseInt(this.data.canvasDefaultVal.maxVal),
      listX = [],
      listY = [],
      rise_val = 0;
    // 绘制 X 轴
    for (let i = 0; i < this.data.canvasDefaultVal.totalX; i++) {
      let val = 0;
      ctx.beginPath();
      meanVal = parseInt(this.data.canvasDefaultVal.maxVal) - mean;
      xMarign += parseInt(this.data.canvasDefaultVal.xMarign);
      mean += parseInt(this.data.canvasDefaultVal.maxValMean);
      ctx.fillText(meanVal, 4, xMarign);
      this.drawing(ctx, 3, xMarign, this.data.canvasWidth, xMarign);
    }
    // 计算获取 1 = ？ 的距离
    rise_val = parseFloat(this.data.canvasDefaultVal.xMarign / this.data.canvasDefaultVal.maxValMean);

    // 绘制 Y 轴
    for (let i = 0; i < this.data.canvasDefaultVal.totalY; i++) {
      ctx.beginPath();
      yMarign += (parseInt(this.data.canvasDefaultVal.yMarign) - 1);
      ctx.fillText(data[i][0], yMarign - 25, this.data.canvasHeight);
      // 绘制线条
      // this.drawing(ctx, yMarign, 0, yMarign, this.data.canvasHeight);

      // 计算绘制圆点坐标
      let x = 0;
      x = data[i][1] * rise_val;
      x = (this.data.canvasHeight) - (x+2);
      ctx.beginPath();
      ctx.arc(yMarign, x, 3, 0, Math.PI * 2, true);
      ctx.fillText(data[i][1], yMarign - 25, x + 10);
      ctx.stroke();
      ctx.closePath();
      ctx.fill();

      // 绘制点线条
      listX[i] = yMarign;
      listY[i] = x;
      ctx.beginPath();
      this.dotDrawing(ctx, listX, listY);
      ctx.stroke();
      ctx.closePath();
    }

  },
  drawing: function(ctx, x, y, X, Y) {
    ctx.setLineWidth(1);
    ctx.moveTo(x, y);
    ctx.lineTo(X, Y);
    ctx.stroke();
    ctx.closePath();
  },
  dotDrawing: function (ctx,xList,yList){
    for(let i=0;i<xList.length-1;i++){
      ctx.setLineWidth(1);
      ctx.moveTo(xList[i], yList[i]);
      ctx.lineTo(xList[i+1], yList[i+1]);

    }
  }
  });