saveCanvas(showToast = true) {
      let canvas = document.getElementById("flash");
      html2canvas(canvas, { scale: 2, logging: false, useCORS: true }).then(
        function(canvas) {
          let type = "png";
          let imgData = canvas.toDataURL(type);
          var bitmap = new plus.nativeObj.Bitmap();
          let filename = "news_picture" + "." + type;
          bitmap.loadBase64Data(imgData);
          // 保存Bitmap图片
          bitmap.save(
            "_doc/" + filename,
            { overwrite: true },
            function(i) {
              //保存到系统相册
              plus.gallery.save(
                i.target,
                function(d) {
                  //销毁Bitmap图片
                  bitmap.clear();
                  if (showToast) {
                     console.log("保存图片成功");
                  }
                },
                function() {
                  //销毁Bitmap图片
                  bitmap.clear();
                  if (showToast) {
                     console.log("保存图片失败");
                  }
                }
              );
            },
            function() {
              bitmap.clear();
            }
          );
        }
      );
    }