大神们好，想canvas画图作为onShareAppMessage的imageUrl，但是为啥我的显示不出来呢？帮看看啥问题吧，非常感谢

//调用cropImg这个函数由imgSrc图片生成一个新的图片保存在headShare 全局变量中

cropImg: function(imgSrc) {

    wx.getImageInfo({

        src: imgSrc,

        success: function(ret) {

            var orWidth = ret.width

            var orHeight = ret.height

            ctx.drawImage(imgSrc, 0, orHeight * 1 / 10, orWidth, orHeight * 8 / 10, 0, 0, 500, 400);

            ctx.draw(false, function() {

            wx.canvasToTempFilePath({

                canvasId: 'attendCanvasId',

                fileType: 'jpg',

                success: function(resl) {

                    wx.saveFile({//把文件保存到本地

                        tempFilePath: resl.tempFilePath,

                        success: function(res) {

                                headShare = res.savedFilePath

               &