DART：实例列表中的 indexOf()

Question

如何获取List中某个Instance的索引？

class Points {
  int x, y;
  Point(this.x, this.y);
}

void main() {
  var pts = new List();
  int Lx;
  int Ly;

  Points pt = new Points(25,55); // new instance
  pts.add(pt);

  int index = pts.indexOf(25); // Problem !!! How to obtain the index in a list of instances ?
  if (index != -1 ){
  Lx = lp1.elementAt(index).x;
  Ly = lp1.elementAt(index).y;
  print('X=$Lx Y=$Ly');
}

Answer 1

  // some helper to satisfy `firstWhere` when no element was found
  var dummy = new Point(null, null);
  var p = pts.firstWhere((e) => e.x == 25, orElse: () => dummy);
  if(p != dummy) {
    // don't know if this is still relevant to your question
    // the lines above already got the element 
    var lx = pts[pts.indexOf(p)];
    print('x: ${lx.x}, y: ${lx.y}');
  }