Only stretch the center of the image in flutter

Question

This is my image:

It's height is 8, but it's width is unknown, maybe 50, 100 or 200.

What I want is the image's left and right side are not stretched when it's width changed.

I use centerSlice but I don't clear it's value:

final bottomImage = Image.asset(
  ImageTool.findVariant(R.calendarMenuBottom),
  height: 8,
  fit: BoxFit.fill,

  //centerSlice: Rect.fromLTRB(10, 4, 10, 4),
);

How can I do it?