完美解决方案，在绘图过程中可能会设置canvas的宽高（this.setData()这是异步的） setTimeout(function () {     ctx.draw(false, function () {     wx.showLoading({         title: '努力生成中...'     })     wx.canvasToTempFilePath({         x: 0,         y: 0,         canvasId: 'longImgCanvas',         success: res => {             console.log(res.tempFilePath);             wx.previewImage({             current: res.tempFilePath,                 urls: [res.tempFilePath]             });             wx.hideLoading();             that.setData({                 isShowLongImgCanvas: false             });         },         fail: function (res) {             console.log(res)         }         })     }); }, 500);