把二维码封装成组件的时候无法导出图片，而且导出图片的时候进入的是初始化方法的callback

[gooczy]

1、exportImage的方法我改成了这个，这样保存图片的时候才能够保存成功，如果canvas封装成组件的话，canvasToTempFilePath要传入当前canvas的实例

QRCode.prototype.exportImage = function (callback) { if (callback && typeof callback === 'function') {

    wx.canvasToTempFilePath({
        x: 0,
        y: 0,
        width: this._htOption.width,
        height: this._htOption.height,
        destWidth: this._htOption.width,
        destHeight: this._htOption.height,
        canvasId: this.canvasId,
        success: (res) => {
          callback({path: res.tempFilePath})
        }
    }, this._htOption.usingIn)
  } 
}

2、另外，在初始化的方法内，生成图片本地链接的方法改成了这个，增加了this._htOption.callback的回调 _oContext.draw(false, () => { setTimeout(() => { this.exportImage(this._htOption.callback) }, 800) })

[zeratel]

if (this._htOption.usingIn) { wx.canvasToTempFilePath({ x: 0, y: 0, width: this._htOption.width, height: this._htOption.height, destWidth: this._htOption.width, destHeight: this._htOption.height, canvasId: this.canvasId, success: (res) => { // console.log('exportImage2'); this._htOption.callback({path: res.tempFilePath}) }, fail: (res) => { // console.log('exportImage3',res); }, },this._htOption.usingIn) 报错是 canvasToTempFilePath: fail canvas is empty , 报这个错是因为调取 wx.canvasToTempFilePath 接口获取不到canvas，

所以原因是上下文的this，各位自行解决吧