Rect.fromLTRB(double left, double top, double right, double bottom)

Construct a rectangle from its left, top, right, and bottom edges.

Source 

Rect.fromLTRB(double left, double top, double right, double bottom) {
  _value
    ..[0] = left
    ..[1] = top
    ..[2] = right
    ..[3] = bottom;
}